F1 interspecific eggplant hybrid “Iron String”

In the 2025 season, three crop breeding projects progressed well. One of them also produced a lot of food. I’ll start with that one: eggplant.

The Iron String

At a get together a few years ago, someone heard I was into gardening, and began talking with me about how they have good success with certain crops like tomato, but one crop they repeatedly failed with was eggplant. At that point I had never tried to grow eggplant, and wanted to know why this was the case. When I asked my uncle he said the same thing, he grows big healthy tomatoes but eggplants never did well in his patch, only making a couple small, spindly fruits. His friend however, grows a fabulous eggplant crop, just like some of the local producers here do also. The thing is, eggplants here demand pampered conditions of high fertility and continual flea beetle treatments. The result in average conditions is stunted, pitiful plants with hardly an eggplant to be harvested. Later on, I came upon an excellent cultivar of the lesser-known eggplant species Solanum aethiopicum. Solanum aethiopicum is sometimes called Ethiopian eggplant or African eggplant. Farmacie Isolde has a great selection of seeds, including Solanum aethiopicum “sweet white”. Many cultivars of S. aethiopicum are bitter, but “sweet white” is not, with a similar flavor to Asian eggplants and a bit firmer texture. Growing African eggplant side by side with Asian eggplant (S. melongena) is a night and day difference— the African eggplant is a much more vigorous and productive crop. Cooler weather doesn’t stunt its growth and neither do flea beetles. In average garden conditions with no amendments it excels. These are the types of traits you want in a crop. In 2024 I planted S. aethiopicum “sweet white” next to an Asian eggplant with wonderful culinary qualities called “Chinese string”. Chinese string produces long, thin, tender and tasty eggplants that are even good raw. As I was evaluating both of these eggplant species, the obvious thing to do was attempt to combine the larger, elongated fruit of the S. melongena “Chinese string” with the general toughness of S. aethiopicum “sweet white.” Both cultivars taste great already. Through this route, a multi-species landrace with hybrid vigor could be developed. I had read in an eggplant hybridization study that in order to recover fertility from hybrids of these two species, the African eggplant must be the maternal parent of the F1 (and then the pollen parent of the back cross). In 2024, I simply took some pollen from the stunted 2 feet tall “Chinese string” plant and placed it onto the stigma of the “sweet white” African eggplant. I had intended to do controlled pollination, which entails bagging and emasculating the African eggplant flowers the night before they open, but never got around to it. It was sort of surprising in the summer 2025 when about half the seed saved from the S. aethiopicum turned out to be interspecific hybrids. Their leaves looked a bit different, many of them had even more vigor than S. aethiopicum, and their flowers were large and purple instead of small and white like “sweet white”. In about half a dozen hybrids, several were sterile and formed zero or just 1-2 eggplants. One seedling was a clear standout, growing almost 2m (6 feet), yielding dozens of long green eggplants, and able to self-support the fruit load without staking. This single plant was astounding in its production, the photos don’t do justice to the absurd quantity of eggplants it made (must've been around 100). For a couple months I’ve been enjoying a delicious Mediterranean pickled eggplant recipe made from it. The outstanding food production was even more noticeable in 2025 due to the daily rain in the first part of the summer lasting 6 weeks. The distant cousins of the eggplants, the tomatoes (including different multi-species hybrids), were weakened by fungal disease were produced no tomatoes during this time. The eggplants thrived however. The S. aethiopicum x melongena hybrids had sterile pollen as expected, but they accepted the aethiopicum “sweet white” pollen. According to an eggplant hybridization study, crossing the F1s back to S. aethiopicum is the only way to restore full fertility to these hybrids. Next year I plan on only growing these back crossed seedlings (75% sweet white / 25% Chinese string), along with the one super vigorous and productive F1 plant grown from cuttings. I am calling this nascent interspecific eggplant landrace “Iron String.”

Passionfruit hybrids

Passiflora crossing was the first crop breeding project I got into. I’ve done a bit of selection of multi-species hybrids for cold hardiness and fruit qualities. It’s a fun genus to work with, beautiful and resilient. Last year I grew a P. incanata x edulis F1 called “Grape Soda Pop” from Dawn in North Carolina. This hybrid has some special traits: it’s able to self-pollinate and has very fertile pollen (especially for an F1). The seeds collected and grown out from Grape Soda Pop in 2025 revealed a mix of outcrosses and self-pollinations. This is the first time I have seen F2s of Passiflora interspecies hybrids. F2 production is primarily hindered by lack of self-incompatibility and by F1 pollen sterility. The outcrossed seedlings from Grape Soda Pop, a blend of 4 species (incarnata, flavicarpa, edulis, and cincinnata), revealed something amazing: some fully fertile seedlings with the ability to self-pollinate. The implication is that the biggest barrier to selecting distant hybrid passionfruits—partially hollow fruit— can be relatively easily overcome using the self-compatible trait from P. edulis. Amazingly, the self-compatibility trait also appears to be able to restore fertility when crossed into other hybrids. There is a phenomenon in some genera where the maternal traits are sometimes actually transmitted through the pollen parent during the initial interspecies hybridization event. Crossing within a species is straightforward: maternal traits are maternal and paternal are paternal. However the disturbance of interspecific hybridization can sometimes flip the script and transfer cytoplasmic traits via pollen instead of seed. Passiflora is one such genus. Therefore, if you want to do Passiflora distant hybridization, I would highly recommend using a self-pollinating P. edulis as the pollen parent to make the initial hybrids. Then you can use the resultant hybrids as seed or pollen parents to transmit self-compatibility and restore fertility to other hybrids. This is essentially a cheat code to speed up and broaden the genetic distance of interspecific passion fruit crossing.

A 4-species hybrid Passiflora seedling with full fruit and self-pollinating ability.

Sweet Potato x I. pandurata

The most unlikely hybridization experiment of 2025 was definitely sweet potato x man-root (Ipomoea batatas x pandurata). Based on all published studies on sweet potato hybridization, there should have been zero seedlings resulting from this cross, and yet it worked great. All I did was place a true sweet potato seedling (grown from an actual seed, not a root tuber) next to a large spontaneously-growing Ipomoea pandurata vine. Besides germinating and cultivating the sweet potato seedling for a couple months, I simply brought the potted seedling over to a nearby yard with I. pandurata, and occasionally stopped by to water it. Not only did the cross work, virtually every flower formed seed (but only when both species were flowering together). A dozen or so hybrids from this cross are currently flowering and twining all over the place in the basement grow room. They have a high degree of pollen sterility, but I’m not going to conclude they’re fully pollen sterile until I get them out in the sunshine with less aphids and more bumblebees. One has red skin with white flesh and another has tan skin with orange flesh. The others I will wait for them to bulk up their roots more. The leaves are more leathery than sweet potatoes, and the vines are more fibrous. You can tell when you take cuttings that they have more fiber in the stems. I haven’t tasted the tubers yet because they’re still small, but the leaves taste fine, similar to sweet potato. With time there will be more data about root quality, fertility, freeze-tolerance and so forth. I’ll be sharing slips of these with a few people for the 2026 season to see how they do in different conditions.

Here is the only seedling so far that I dug out and inspected the roots. Note the leathery leaves, hinting at drought tolerant traits from I. pandurata.

Goji

One crop I’ve worked with, but that got put on pause in 2025, is interspecific Lycium hybrids. Luckily, Michael Longfield of Interwoven Permaculture was able to make further progress on this front. The three species goji seedlings (“triple” goji) in my yard are in too much shade and not fruiting, so I sent one off to Michael. Around the same time, he started growing a cultivar which is the pinnacle of Chinese goji breeding called “Gigantic Ningxia.” He crossed the triple hybrid goji with the pollen of the gigantic goji. The basic idea is to combine large fruit with the more vigorous, humidity/mildew tolerant nature of L. chinense. With some black goji genetics in the background, seedlings with large purple fruit and juicy texture can be selected. Additionally, large leaf sizes could show up as well for a dual purpose leaf/fruit crop.

Photos of one of the “triple goji” seedlings, courtesy of Interwoven Permaculture. The color changes with ripeness, which is a trait shared by the maternal parent of this seedling called “Stardust.” The pollen parent of this group of seedlings was Lycium chinense “large leaf.”

Some thoughts

A highlight from these 2025 season crosses is that parental selection is very important. Certain parents are able to promote the fertility of distant hybrids and essentially act as “super-parents.” With other parents, its about another special quality such as insect resistance or fruit size, which can be equally important factors in determining the usefulness of a crop. Another salient point, seen in the sweet potato x pandurata cross, is that you sometimes want to strategically limit diversity in order to expand it. If I had placed several sweet potato seedlings next to the I. pandurata vine, its highly likely that no hybrids would’ve been obtained because of the competitive advantage of the sweet potato pollen. All of the progress in a short amount of time on these various projects brings up the need for more growers to further develop these lines.

The first seedling to flower, the anthers had reduced production of clumpy pollen.

At the end of the first essay on the sweet potato heterospecific pollen experiment, it started to become clear that the seedlings were going through genome shock. As they have continued to grow, they seem more and more to be a big F1 hybrid family. Here are some observations and tentative conclusions about them up to this point.

Currently the seedlings are vining out and setting many flower buds. This twining growth habit is itself an interesting thing. Typically the climbing or twining trait is relatively uncommon in sweet potatoes, which have been mostly selected for bushy or trailing growth. Trailing refers to the cascading habit that you see often in ornamental potted sweet potato cultivars. Twining refers to long climbing stems that want to go upward and wrap themselves around something. In Sweet Potentials pt. 1, I mention that a rabbit pruned a sweet potato seedling that was twining up a chicken wire enclosure. I decided to root that cutting and use it as the seed parent for the cross. There was a selection process at play there, because only one seedling in that patch of ~25 had the ability to go vertical and twine around the chicken wire. That seedling had thin, hairy, twining stems. This is a more wild phenotype that sometimes show up in sweet potato seedlings. It is considered to be an ancestral throwback to I. trifida, one of the species that makes up the sweet potato genome. Climbing is also the general growth habit in the Convulvulaceae family. During the domestication process of sweet potato, the climbing habit was selected against, shortening the vines so they can put more energy into root production. The sunnier, less competitive context of the cultivated field also made climbing much less necessary. Through domestication the sweet potato stems also got thicker and lost their hair (“pubescent to glabrous”).

With the unexpected success of this distant hybridization experiment, I have to wonder whether the wild-looking seed parent was part of the reason behind it. It could be the case that domestic phenotypes have increased the crossing barriers in the flower, which can happen during a long-term domestication process. It must also have something to do with the general fertility of the sweet potato seedlings that were used, having already been selected over years to produce many flowers and seeds. This is a significant difference in experimental conditions compared to every published scientific study on sweet potato wide hybridization, which exclusively used vegetatively propagated I. batatas accessions. Typical sweet potato cultivars have highly reduced seed set and sterile pollen, diminishing the potential for both homospecific and heterospecific crosses. The idea in setting up this experiment was to test this hypothesis — would a young seedling be more open to distantly-related heterospecific pollen? Even after only a couple years of cloning, sweet potato seed production is known to be lower than its first season from germination.

Reading the other essays here, the influence of Ivan Michurin’s principles and methods of plant breeding is clear. One of Michurin’s tips to increase the odds of distant hybridization is to use a seed parent (particularly a hybrid) in its very first flowering. I had this in mind with this experiment, also because sweet potato is a highly heterozygous 3-species hybrid. Additionally, the fact that sweet potato has very little chromosomal barriers to distant hybridization makes it very promising to generate new multi-species swarms. The wide crossing barriers in sweet potato are fairly strong, but they mostly happen in the flower (source).

Another tip from Michurin is to never let hybrid seed dry out. Wide hybrid seeds can contain much more fragile embryos than a normal seed. Even a little bit of dryness can greatly reduce the seed viability. Hybrid seed must be immediately placed in moist media for germination or cold stratification. This is why my sweet potato seedlings are growing currently under lights in winter.

One aspect of wide hybrids that Michurin discusses extensively is their plasticity. The sweet potato hybrid seedlings have unsurprisingly shown a significant degree of plasticity. At first, the behavior of the seedlings was very confused and chaotic. They grew extremely densely, with nodes stacked one on top of the other. The leaves were crinkled with intervein chlorosis and patchy pigmentation. These signs are similar to a viral infection, yet the seedlings were mostly able to resolve these issues with time. The crinkled yellowish leaves started looking more normal just as the seedlings began growing well and vining out. Even the runty seedlings that started nearly albino later recovered and starting producing chlorophyll. Some unusual characteristics that persist are leathery bronze-ish leaves, altered leaf venation, and flower sepal changes.

A photo showing the lack of internode space and malformed leaves of the initial growth:

As the seedlings stabilized some, their twining nature was revealed. The seed parent did have the primitive, less-domesticated phenotype (thin twining pubescent vines) but was clearly the odd one out among its siblings in this regard. But just how uncommon is the climbing trait in sweet potato seedlings? Having grown out only ~30 seedlings this year, I couldn’t conclude much. Several sweet potato studies mention the climbing trait, usually in a list of traits to be selected against. There is a single paper on breeding sweet potatoes for the vining trait. In St. Croix in the early 80s, the Caribbean Food Crops Society wanted to produce vining sweet potatoes to compete better against weeds and climb up support plants like corn in polycultures (source). This breeding project was directed specifically at small farms with diverse crops. The paper gives data for the rate of occurrence of the climbing habit. In a group of 3000 seedlings from diverse sources, only 21 were climbing. After two additional rounds of poly-crossing the climbers, the trait increased to around 50%. However, many of the climbers resulting from the poly-crosses had a virus like syndrome and didn’t thrive. It’s an interesting paper that’s worth taking a look at.

In the case of these distant hybrid seedlings, all of them so far are climbers, a highly unusual distribution for that trait. Such a skewed distribution appears to be a result of hybridizing a vining sweet potato with a vining wild relative. This also reduces the chromosome number from hexaploid down to tetraploid (in theory). The entire tapestry of evidence so far, from the genome shock to novel traits like leathery leaves with unusual venation, makes a compelling case for distant hybridization. Besides being all vining, many other traits vary dramatically among the seedlings such as leaf texture, leaf size, leaf shape, stem thickness, and pubescence.

The below photo shows stress from genome shock (malformed, yellowish leaves with exudates on the veins) as well novel traits (leathery leaves with altered venation):

Another interesting feature of the hybrid seedlings is the sepals, which are a key identifying feature for Ipomoea species. In these seedlings, the sepals are long and tapered compared to I. batatas. Also, the calyces are loose and star-like instead of cupping the bud tightly like batatas. These features are both consistent with I. pandurata influence.

I. batatas sepals are 6-12mm in length, often on the lower end, whereas the seedling in the above photo has sepals about 14-16mm. Another identifying feature is the outer sepal to inner sepal size ratio of a calyx. In sweet potato, outer sepals are shorter than the inner sepals, with respective lengths of about ~7mm / 11mm. Pandurata on the other hand has close to an equal ratio of outer to inner sepals, with lengths of ~15mm / 16mm (source).

The next update on these seedlings will probably be the end of January. Hopefully the impressive combining ability bodes well for fertility and future intercrossing. One powerful thing that this experiment shows is that wide crossing barriers can be selected against. Regardless of whether the selection is developmental (first flowering) or genetic (intrinsically more permissive flowers), with the right conditions sweet potato distant hybridization is able to easily go much further what has been reported. Tricks such as plant hormones aren’t necessarily required to generate a hybrid population. Other vegetatively propagated crop species may also be able to relax their crossing barriers by similar methods.

…much of the research reviewed here is beginning to show that the distinction between what we class as hybridization, transformation, and LGT [lateral gene transfer] may be less discrete than we first thought.

The mechanisms underpinning lateral gene transfer between grasses

Looking into studies on cross-pollination, there are a variety of interesting phenomena such as the mentor effect, xenia effect, pollen-induced genome shock, and lateral gene transfer. This essay discusses some of these phenomena in the context of a sweet potato experiment and plant breeding generally.

Sweet potato is an interesting crop. It is as a segmental allopolyploid, a thorough blend of three progenitor species with additional copies of chromosomes (source). Another fascinating aspect of the sweet potato is that it has acquired DNA laterally from Agrobacterium tumefaciens. This bacteria naturally occurs in soils, occasionally showing up as crown gall on plants. Plant scientists use this bacteria to facilitate genetic transformation or horizontal gene transfer. Therefore, the sweet potato is considered the first naturally transgenic crop (source). These aspects help explain why sweet potato seedlings are reported to have a higher plasticity than most crops, sometimes spontaneously changing phenotype.

This season was my second time sowing sweet potato seeds, which are not an easy thing to find. Although sweet potato is naturally a highly diverse crop, years of vegetative propagation have reduced its ability to make seed. Since a small number of independent plant breeders have been working to restore sweet potato’s ability to produce seed, this is starting to change. Seed that has already undergone selection for fertility is a head start allowing the latent diversity to be more easily unlocked. Last year, I grew just 10 seedlings. One had large white-fleshed tubers which never turn sweet despite long storage time. A lucky find, since was hoping for one that could be used in potato recipes.

The year I germinated and planted about 30 seedlings. For a few years I’ve been wanting to experiment with planting a single sweet potato seedling next to the wild relative species Ipomoea pandurata. The idea was to see how a fertile young I. batatas seedling would react to pollen from a distant wild species. There’s also an old Russian paper on Ipomoea distant hybridization that reported a low rate of seed set using I. pandurata pollen on sweet potato (source). My expectations were not high though, as Ipomoea is known to have fairly strong distant crossing barriers.

In sweet potato, interspecific hybridization takes place with varying degrees of success with closely related species in the Batatas section (source, source). One of the species sweet potato can cross relatively well with is the wild relative I. leucantha, which grows wild in the US and is weedy like many Ipomoea. Perhaps a self-sowing tetraploid sweet potato could be developed from this combination? Hybridizing sweet potato with a distantly related species like I. pandurata however is much more difficult. Some experimenters have made thousands of pollination attempts between distantly related Ipomoea species without success. In recent years however, researchers have made progress bypassing sweet potato’s distant crossing barriers using plant hormones. A mixture of GA3 and BA6 applied to the flower stalk for 10 days following pollination keeps the flowers from dropping and allows the hybrid embryos time to develop. Between 1/40 and 1/50 pollination attempts with this technique yields a distant interspecific sweet potato hybrid seedling (source). Five new interspecific sweet potato hybrids have been developed this way, each with a different distantly related pollen parent (hederacea, muricata, longcophylla, grandifolia, and purpurea). Surprisingly, these hybrids are very fertile (all but one are tetraploid). These studies reveals that the crossing barriers of sweet potato and its distant relatives exist primarily in the flower and early embryo development stage. The authors recommend new sweet potato interspecific hybrids be synthesized using this method. The full fertility of these tetraploids allows them be inter-crossed to develop complex multi-species sweet potato hybrids. Such crosses could thrive with lower effort in a wider array of ecosystems and conditions. Temperate perennials such as I. pandurata could offer winter freeze resistance to sweet potato tubers (hopefully without the disgusting glue).

One morning this summer (2025) a rabbit left a freshly pruned shoot of one of the sweet potato seedlings on the ground. I rooted it, took it to another garden, and placed the pot next to the wild I. pandurata vine. As the sweet potato started to flower, the pandurata vine was already huge with plenty of flowers. When virtually every flower on the sweet potato began to set seed, the seedling appeared to be self-pollinating. Although many sweet potato seedlings cannot, some self-pollinate very well. Interestingly however, when the pandurata vine stopped flowering in the beginning of September the sweet potato set no more seed, despite the 6 weeks or so of relatively warm weather that followed. It seemed like the I. pandurata pollen was physiologically active on the sweet potato flower. The simplest explanation is the distant “heterospecific” pollen caused the sweet potato to self-pollinate. In fact, polyploids like sweet potato are more likely than diploids to facultatively self-pollinate when exposed to heterospecific pollen (source). This pollen stimulation effect is called the “mentor pollen” effect. The term mentor pollination goes back to Ivan Michurin, who would apply a small amount of compatible pollen together with a more distant pollen to promote hybridization (he also used pollen mixes). The mentor pollen effect was later extended to include also instances where distant incompatible pollen induces self-pollination. Therefore, any pollen that acts to overcome incompatibility barriers can be referred to as mentor pollen, whether it’s a distant species, the same species, or a pollen mix. Considering that self- and cross-incompatibility barriers can have shared underlying mechanisms, the mentor pollen effect is an appropriate term whether applied to homospecfic pollen promoting outcrossing or heterospecific pollen causing self-pollination.

Upon harvesting the seed from the sweet potato exposed to pandurata pollen, it looked immediately distinct from the other sweet potato seed. The rest of the seeds, harvested in another garden with about 25 seedlings, were black (with a few brown ones). In a typical sweet potato, as the seed capsule matures and gets drier, the seeds go from brown to black. These mature seeds harvested near the I. pandurata however were light tan with dark spots, much lighter than even unripe brown seeds. Regardless of the stage of maturity or dryness of the seeds, they were clearly distinct and recognizable in a bag with the other sweet potato seeds. Having grown only a small number of sweet potato seedlings, I reached out to someone with more expertise, the person (Reed) who had originally developed this line of seedy sweet potatoes. He didn’t recall seeing any seeds like the tan spotted ones despite growing hundreds of seedlings over the years. This seems to suggest that the I. pandurata pollen was physiologically active down around the ovary of the sweet potato flower, altering the coloration of the seed coat. Although the seed coat is maternal tissue, heterospecific pollen can nonetheless affect its developmental expression. This phenomenon is called xenia when the pollen successfully fertilizes the emybryo. The related term metaxenia refers to heterospecific pollen altering maternal tissue while causing either self-pollination or clonal (nucellar) embryo formation.

Photo of the Ipomoea batatas seeds exposed to I. pandurata pollen:

When the seed capsule is brown but the pedicel is still green, the seeds are white with light spots. Once the flower pedicel is fully dry and the seed mature, the seed darkens and the spots become distinct. The not fully ripe white seeds were blown off by strong winds, but they still germinated.

Metaxenia/xenia effects originate at the interface where the pollen tubes meet the ovary. The combination of RNAs, hormones, and other biomolecules shed by the pollen can cause developmental shifts in the embryo even without fertilization. For the resultant seedlings, this stress can range from temporary epigenetic perturbation to a full genomic shock with transposon mobilization. In rice, intergeneric pollen has been used to select “mutator phenotypes” with a high degree of continuing variation.

When genetically analyzed, the seedlings were found to have close to 100% rice genome. In spite of the Zizania pollen not fertilizing the rice, a very small portion of its genetic material was able to transfer laterally into the rice embryo. The <.1% Zizania genes that transferred into the rice were found to be primarily transposons. Transposons are like the genomic version of weeds, during disturbances they come out of dormancy and spread. As they cut- and copy-paste themselves around, sometimes they make it into adjacent disturbed systems (horizontal transposon transfer).

“Overall, these experiments prove that the presence of heterospecific pollen from distant species during pollination can promote TE mobilization and transfer of genomic DNA from the donor species in the recipient genome. Although it is not clear where, when, and how the DNA exchanges happen, the presence of foreign pollen is enough to contaminate the reproductive process, without further human intervention.” (source)

Horizontal transfers to the embryo have even been made in several crops by simply dropping a solution of genes into a cut style hours after pollination (pollen tube pathway mediated transformation). In another set of experiments, the pollen itself is made a vehicle for genetic exchange (pollen tube mediated transformation).

Beyond the strange seed coat color, these 6 batatas seedlings seem to have a higher degree of general weirdness—two are low chlorophyll mutants, another appears to be polyembryonic (in this case two embryos in the same seed), and another is showing variegation in its first true leaf. I sent photos of them to a few true sweet potato seed growers. The only person who saw multi-stemmed seedlings (Reed) reported that he found them in the years his sweet potatoes grew next to a wild I. pandurata vine. Low chlorophyll mutants were estimated to occur less than 1% of the time. Based on these limited observations, the tan spotted sweet potato seed seem to contain embryos with a higher degree of plasticity than is typical. The application of foreign pollen to sweet potato, under certain conditions, appears to have potential as a selective force.

Photo: two partially fused seedlings from the same seed. Note the different stem colors.

Again, most likely the seeds were self-pollinated and gained a bit of plasticity from I. pandurata pollen signals. It’s also not out of the realm of possibility that some of the seedlings are true distant F1 hybrids, or even partial hybrids with small bits of laterally acquired genetic material. Regardless of the degree or nature of the variation of these seedlings, plant breeding experiments like these make us keep an open mind about possibilities and boundaries. Categories of selfing, crossing, lateral gene transfer, and vertical gene transfer are not always as rigidly distinct as we think. The sweet potato itself is already an example of blurred categories—bacteria/plant, natural/genetically engineered. In fact, the laterally transferred agrobacerium genes aren’t simply dormant traces of an ancient event, they are actively expressed in the sweet potato (source).

“the [sweet potato] plant can produce agrocinopine, a sugar-phosphodiester opine considered to be utilized by some strains of Agrobacterium spp. in crown gall”

Sweet potato produces agrocinopine just like an actual plant gal. In a real sense, the sweet potato is part cultivated gall. Agrocinopine allows agrobacterium to utilize the plant for energy.

These sweet potato seedlings provide an excellent opportunity to test the idea that plasticity can be amplified across generations by repeating the stress. Off-type seedlings are selected, exposed to heterospecific pollen, the seed harvested, and repeat. Like the successive grafting experiments, this could have a snowball effect that intensifies seedling plasticity. Successive heterospecific pollen exposure might also be able to condition and select the batatas seedlings for more complete cross-fertilization between the two species.

Ecology has two main branches, the study of individual organisms (autecology) and the study of ecological networks (synecology). The uniqueness of ecology that separates it from biology comes from community ecology (synecology). Therefore, an ecological view of heredity and plant breeding is likewise process-oriented. Rather than just steering allele frequency, its about managing feedback systems of stress, exchange, and plasticity. In addition to the bottom-up selective pressure of individual genes and organisms, community ecology reveals that network feedbacks are a top-down selective force. The units of selection become dynamic networks.

“By using sequencing approaches, we aimed to characterize horizontal transfer of genetic material, primarily eccDNAs, from donor goji cells to recipient tomato cells across the graft junctions and in subsequent regenerants. This transmission led to substantial pleiotropic traits in the tomato plant, which was designated as ‘Go-tomato’...These findings have high potential for the asexual production of crops, for example, by using a grafting system in the Solanaceae family plants, which considerably extended the growth cycle of the grafted plants in the field. Furthermore, the unique attributes of mobility and replicability of eccDNAs highlight their potential as vectors for horizontal DNA transfer through asexual grafting approaches.” (source)

Intro

The primary impulse for writing this essay is a recently published study on an interesting new method of graft hybridization. This technique had the amazing result of generating a cold-hardy perennial tomato, dubbed the “go-tomato.” I came across this method a couple years ago looking up Chinese patents involving various kinds of goji / tomato grafts. Goji / tomato grafts are a fairly broad research area, and have been used to improve both species with traits such as tomatoes with medicinal polysaccharides and goji berries with larger fruit, meaty texture and low seed count. Below is a depiction of the process of go-tomato development. Grafting transferred a variety of mobile eccDNAs from goji to the tomato scion. Novel phenotypes were selected and propagated vegetatively first via adventitious roots and then axillary buds. The go-tomato gained perennial growth habit, improved fruit quality and hybrid vigor.

Before discussing the go-tomato graft study, I want to highlight two techniques for generating graft chimeras. They are useful methods because they don’t involve tissue culture and have a high rate of efficiency. The original technique to synthesize chimeras only had 1% success rate. A graft chimera in horticulture typically refers to a periclinal chimera, where one species or cultivar occupies the outer layer and a different type occupies the interior. One such example is the cold hardy citrus chimera “Prague.” It has a sweet mandarin flavor but is more cold hardy than any mandarin by virtue of the Poncirus trifoliata tissue layer. As vegetatively propagated cultivars, chimeras will over time accumulate viruses and lose vigor, but this process can take hundreds of years, and in that time many new ones can be synthesized relatively easily. Although seed saved from such cultivars will not have a graft chimera phenotype (the seed is produced by only one tissue type), genetic transfer has been shown to take place across the different layers. The seedlings are therefore likely to display graft induced variation and hybrid vigor. If you can grow seeds from a chimera, see what you get. Instead of chimeras being held in distinction to graft hybrids, they can therefore be considered a type of graft hybrid. Chimera synthesis is primarily done in woody species. It can work for herbaceous plants when they are evergreen or when they die back to a rhizome (but not a true root since its made from a single layer).

DHS

The first technique is called DHS (direction-hormone-slowlygrowing). It has a 20% efficiency rate, which is very good (source). DHS involves approach grafting two seedlings together, cutting one of them at an angle, and applying plant growth regulators to induce shoot formation. The selection phase involves watching for slowly-growing shoots, an indication of chimerism. With the DHS method, periclinal chimeras to be selected early on in the seedling stage. With a couple trays of seedling grafts, several new periclinal chimeras can be selected in a small space. Read more details in the original paper.

Bud Splicing

This method was developed by Dr. Nassar at the University of Brasilia working on Manihot species. The success rate in cassava is 15%, and while it’s slightly lower than the DHS method, it has the advantage of being simpler and not requiring any plant hormones. This is the first time an efficient technique has been developed that requires neither tissue culture nor hormones. I recommend reading Dr. Nassar’s paper on chimeras, as there is a lot of interesting information on the subject. Bud splicing differs from a conventional splice or whip graft by cutting and aligning two different growth buds.

Go-Tomato!

The go-tomato paper (Nov 2024) shows a novel technique for graft hybridization. Tomato seedlings are grafted onto goji rootstock (somewhat lignified but still green). As the tomato scions heal they form adventitious roots (ARs) just above the graft union. In some grafts, these roots are larger and more vigorous. The original patent for this method called these chimeric roots, but the now published paper confirms that these are in fact tomato cells that have undergone horizontal genetic transfer from goji, rather than a cell fusion or periclinal chimera. The tomato scions with the vigorous roots are then cut off, leaving behind the entire graft union and goji rootstock. These tomato cuttings are then planted out in the field. Over the next few months, underground shoots can arise in the space between the hybrid roots and the ground level. These shoots display novel phenotypes at least 10% of the time. From these modified axillary shoots, the new goji-tomato graft hybrids were propagated and given the name go-tomato.

“Remarkably, plants with unique phenotypes in regenerated adventitious roots or buds had an extended growth cycle; they flourished for approximately 24 months in the field as compared to the typical 8-month growth cycle of [tomatoes]. These plants were successfully cultivated perennially with excellent performance (particularly high yield and fruit quality) in the temperate regions of Zhejiang and Shandong and the plateau areas of Qinghai Province, China, which are characterized by low temperatures and a wide diurnal temperature range. This dramatic extension in the duration of tomato growth was attributed to the perennial trait acquired from goji.”

These go-tomato graft hybrids were found to have 71 extrachromosomal circular DNAs (eccDNAs) transferred from goji. These small circles of DNA are mobile and able to self-replicate. The eccDNAs are also taken up by other cells. In this case, goji eccDNAs were taken inside the cells of the tomato, but not integrated into the genome. The greatest density of goji eccDNAs was found close to the graft union. Only a few goji eccDNAs made their way up into the leaves of the tomato.

Let’s go over again the steps of this experiment: (1) grafting tomato onto goji causes adventitious roots to form right above the graft union, (2) some of these root systems show hybrid vigor, being larger than either species, and (3) when these hybrid root systems are cut off (leaving behind the graft union) and planted in the field, at least 10% the time shoots with unusual phenotypes arise near these vigorous (now underground) roots.

The go-tomato study reveals a high density of transferred eccDNAs close to the graft union. However, without adventitious roots forming there displaying unusual phenotypes, the go-tomato cells would not have been multiplied or noticed. It’s possible that the development of roots in proximity to the graft union also played a role in promoting these horizontal transfers. The go-tomato technique appears to be a two step process for amplifying cells with eeCDNA transfers. Since the eeCDNAs do not travel far, they first multiply within the adventitious roots near the graft union, and again within the axillary buds near these roots.

Some thoughts

The authors of the go-tomato study recommend repeating the experiment with other Solanaceae family crops. Goji rootstock can potentially transfer perennial growth habit, cold tolerance, vigor, and improved fruit quality to other nightshade family species. Many rootstock/scion combinations in this family and other plant families should also be experimented with. Even where there is delayed incompatibility between distant grafts, there is usually enough time for adventitious roots with eccDNA transfers to form. Although these transferred traits are stable over time through asexual propagation, can the eccDNAs be transmitted through seed? More research needs to be done to answer this. The goji eccDNAs exist and self-replicate inside of the tomato cells, although outside of the chromosomes. It’s possible that the eccDNAs can indeed transmit into the pollen or maternal tissue during reproduction, and therefore those traits transmit via seed, but it’s also possible that they are lost in the process of seed development. However, even without eccDNA seed transmission occurring, the seedlings from the go-tomato could nonetheless display novel variation through mechanisms like novel RNAs, epigenetic alterations, and so on. It’s worth noting that sexual hybrids between goji and tomato have been made via embryo rescue, yet are sterile according to one study.

Lessons from the go-tomato experiment:
Try to get shoots and or roots to form close to the graft union, so they can take up and hopefully express some of the genetic material in higher density there as they develop. Air layering could be done if roots do not form spontaneously. Other tricks like pruning the scion apex might help adventitious roots or shoots from close to the graft. Bending the grafted shoot horizontally may also cause shoots to form near the graft union. Plant hormones such as auxins and cytokinin, combined with wounding the area near the graft are also common methods to induce shoots or roots. The scion should be a seedling, but the rootstock can be a cutting. Keep an eye out for and select based upon phenotypic changes.

Double graft:
In light of the go-tomato study, it’s interesting to consider the mentor graft technique called the “double graft.” This technique has an unusually high transformation rate for a first generation mentor graft, close to 70% of the seedlings show novel variation. The seeds are collected from a shoot that emerges from a bud in between two grafts. No other shoots are allowed to develop on the (annual) plant. The double graft experiment satisfies similar conditions to the go-tomato method in that the shoot develops in proximity to graft unions. This could explain the high rate of seed transformation produced by this technique.

Promoter compounds:
There are some compounds used to promote horizontal gene transfer that are relatively available and safe. These should be tested also in the context of promoting graft transformation. For example, polyethylene glycol (PEG) promotes horizontal gene transfer through endocytosis. PEG could be sprayed on a grafted flower stalk or axillary bud developing near a graft union. In general compounds which induce stress response and cellular membrane permeability are helpful in the right doses.

Stress:
In addition to highlighting the importance of eccDNAs in graft induced variation, the go-tomato study also adds to the growing body of data showing the importance of stress responses in horizontal genetic transfer. Here are two relevant quotes from the paper:

“The biogenesis of transposon-derived eccDNAs is associated with plant stress response, thus indicating that active transposable elements may provide substrates for DNA integration, displacement, recombination, and gene capture, thereby enabling plants to rapidly develop novel stress responses.”

“Under stress conditions, chromosomal DNA consistently generates substantial quantities of extrachromosomal DNA fragments (Bakhoum et al. 2018). The remarkable stability, mobility, and self-replication capacity of eccDNAs in animals make them exceptional vehicles for transmitting and amplifying signals between cells.”

If you have read the other essays on here, you’ll be familiar with the emphasis on lining up various stress conditions such as grafting and mentor pruning young hybrid seedlings in order to achieve a higher rate of transformation. The cellular repair mechanisms that activate in response to stress are key to promoting this process. For example, rotifers that undergo the stress of desiccation have a higher degree of horizontal gene transfers (source).

Experimental Patreon

I am considering starting a Patreon (or the like) where I post video updates on various plant breeding experiments. This would encourage more energy put into the experimentation side which I enjoy. Video format allows for more quickly posting updates showing and discussing experiments through time. The experiments I have in mind are the kinds of ones I have been writing about here such as alternating magnetic field pollen/seed treatment, distant hybridization trials, graft hybridization, pollen-mediated gene transfer, msg mutation, exposing pollen/seed to mini Tesla coils, and so on. One of the top priority projects will be testing goji wide hybrids for interfamily graft capability, to hopefully select a freeze hardy woody universal graft adapter.

Gardening and plant breeding is for me, at least currently, oriented more around learning and enjoyment versus efficiency and progress. It’s one way to justify being a generalist grower in a small space with minimal resources. Under these circumstances, the extent of progress on a given crop depends as much on serendipity as persistence.

Working with vigorous species allows a bit of wiggle room within time and energy constraints. Tough perennials in particular are relatively self maintaining, though it’s a double edged sword, since it removing the ones you don’t want can be difficult. In my garden, the intermingled rhizomes and vines of passiflora hybrids are an example of this, making it challenging to either isolate or remove individual seedlings.

Among the the hybrid passiflora seedlings (incarnata, flavicarpa, cincinnata) grown out this year, there are a few standouts. One has double-sized white arils (the edible gel around the seed) shaped like teeth. Another has a strong banana scent and flavor. One seedling has aromatic orange arils not too different from the Brazilian passionfruit ancestor. These are a few generations away from the original F1 hybrids. Many seedlings have unique and wonderful flavors. They are cold hardy to at least 4F/-15.6C . It’s interesting seeing how various traits recombine in a multi species hybrid group as you go down the generations. Many seedlings are of course subpar—poor fertility, mediocre flavors, chlorotic leaves, or very small fruit. However many seedlings have excellent traits that I consider significant improvements over the average P. incarnata. A cold hardy passionfruit breeding program has a lot of potential to combine beneficial traits such as juicy arils, neutral seed taste, tiny seeds, big arils, clumping rhizome habit, and a wide variety of flavors/aromas.

Photo of cold hardy passionfruit hybrid lines. The top two are 5th generation crosses of P. incarnata, flavicarpa, and cincinnata. Bottom left is incarnata x edulis “grape soda pop” (from a breeder in North Carolina) and the bottom right is a 4th generation incarnata / tucumanensis seedling.

Another genus that I enjoy working with is Polygonatum or Solomon’s seals. I was blessed to receive seed from the rare species P. darisii, most of which turned out to be hybrids with the P. huanum (frequently misidentified as P. kingianum). These species have the same chromosome number with no inter-fertility problems. A few seedlings flowered in 2024. They are strikingly beautiful plants. The species in this group (the kingianum group) are sought after ornamentals, but in Asia they are also used for starch and medicine. Polygonatum darisii has the largest rhizomes in the entire genus that can be up to 1kg (2.2 pounds). The roots are typically steamed then dried. They are toxic raw. It’s common for a rhizome to be added to a broth as a nutraceutical. In the next couple years I should be able to generate enough F2 seedlings to make interesting selections. I also cultivate a few other species in different parts of the genus.

The cucurbita lundelliana x ficifolia project is starting to pick up speed. The F1s are highly dominant for lundelliana traits, everywhere except the flower shape which is intermediate. The F1 fruits are slightly larger than lundelliana but otherwise look exactly the same. Many of the F1 seedlings didn’t flower, or flowered very late. Luckily, a collaborator Tom sent me a bunch of fruits from his F1 seedling. This winter and spring I’m sending seed to several growers for crossing back to domestic Cucurbita species. They should cross easily to either C. moschata, maxima, or ficifolia. It’s likely they will be able to cross with pepo after prior crossing with moschata, which which acts as a genetic bridge. In any case, they need one more cross to a domestic species (as the mother) to have enough domestic traits like large fruit that is not bitter and fibrous.

Photo of an F1 C. lundelliana x ficifolia flower on the left. On the right: F1 fruits in between each parent species.

Some kitchen garden cultivars / species that made the cut this year: Italian cabbage turnip, Capsicum baccatum CAP455, Capsicum chinenese “habanada”, and Cucumis anguria. A couple of seedlings of Cucumis anguria produced large fruits, with the biggest about 8 times the size a normal anguria. I also found a seedling of chrysanthemum greens (Glebionis coronaria) that didn’t die after flowering in the spring. It kept flowering and producing tender greens all the way through early winter, so I rooted cuttings of it.

Photos of the large Cucumis anguria in comparison to a typical sized fruit (on the left).

A view to next year

Sharing with other growers the vigorous (and space hogging) Cucurbita and Passiflora hybrid seeds will allow me to focus more on trying some new crosses. One is the ambitious (though doable) attempt at a cold hardy hybrid sweet potato. Sweet potato has the ability to make wide hybrids with other species across large genetic distances when plant hormones are applied to the flower stalk for 10 days after pollination. It will take a lot of work, but there are many reasons to do it.

I also hope to make more Lycium crosses, such as crossing stardust goji (black x yellow) with Lycium carolinianum and a huge sweet goji from Ningxia. I’m a fan the Physalis genus, so I’m looking forward to trying P. longifolia x tomatillo. A friend had success in 2024 growing out and back crossing F1 seedlings of P. longifolia x tomatillo, so there seems to be a lot of potential for physalis hybridization. A perennial ground cherry with a larger fruit would be great. Cucumis ficifolius x anguria is another cross I hope to attempt in 2025, which is supposed to yield very vigorous seedlings that are inter-fertile. According to one source C. ficifolius has fruits that store in the pantry for six months. If the storability trait can be combined with the large fruited anguria it could be a useful vegetable, something like an insect and disease resistant storable cucumber with the ability to self-seed.

In 2025 I look forward to further experimentation with herbaceous grafts. They are not hard to make and heal, but the weak point for me has been gradually reducing the humidity to ambient levels afterwards. In order to automate this, I connected a terrarium fogger with a built in timer to the graft healing chamber. Herbaceous grafts also require a little more care when hardening-off (adapting outdoors).

Another experiment for 2025 is magnetic pollen treatment, which goes back to the work of one of the original mutation breeders Alberto Pirovano. Nobody in the last 100 years seems to have tried replicating his magnetic pollen treatment experiments. Although of course it may not work, scientific studies exist which hint at potential mechanisms that could underly it. At least it’s simple to test, requiring only a blender, neodymium magnets, and a plastic bag. This setup exposes the pollen to rapidly alternating rotating magnetic fields up to 2,000Hz (depending on the blender speed and the number of magnets).

Whether your work is messier like a young ecosystem or more like a streamlined, high through-put old growth forest, both sides of the process are necessary for development. Regardless of your particular constraints, joy and openness will surely lead you to the right path.

Taking a look at the studies done over the decades sheds light on some of the relevant factors. Some methods will be a better fit for particular conditions or to the growth pattern of a species.

Fig 1: double graft on the left — tender bud graft on the right, two of the most successful methods (source). Note the double graft has two scions.

—age—

Zu and Zhao (1957) investigated the effect of scion age on the rate of transformation. They mentor grafted white eggplant scions of different ages on purple eggplant rootstock, and then grew out the self pollinated white eggplant seed (source). Any purple coloration appearing in the white eggplant seedlings would be an easy to notice influence from the graft. The cleft graft involved a relatively older white eggplant seedling as the scion. As the scion grew, pruning was done to reduce the surface area of its’ leaves. The rate of purple seedlings grown out from the cleft grafted white eggplant averaged 6.67%. This is consistent with some other researchers who found the rate of transformation of seedlings to be around 1-5% (source). It may seem like a low rate, but it’s much higher than the spontaneous rate of mutations. The tender bud grafting method involves plug grafting a cotyledon stage scion into the older rootstock around 22cm tall. The tender bud-grafting method produced purple eggplant variants at a rate of 19.78%. This experiment illustrates the increased plasticity of very young seedlings compared to older ones. In this case, the transformation rate tripled, up to about one in four seedlings.

Developmental age was also found to be a factor in breaking down crossing barriers between domestic tomatoes and the wild species Solanum peruvianum. Only the young seedling grafts were able to be hybridized upon flowering. Slightly older seedlings under the same conditions retained the hybridization barriers.

— leaf pruning —

The mentor grafting technique involves pruning all of the leaves of the scion except the 2-3 at the apex, making the pupil plant almost totally parasitic on the mentor plant. The amount of leaf biomass on the pupil (the plant to be transformed) is inversely proportional to the mutation rate. The distant graft mutagenesis studies reveal a rapid drop off in the mutation rate as more leaves of the scion are retained (source). Japanese researchers studied this technique for many decades using a variety of Solanaceae family plants.

Depiction of a typical graft A) compared to a mentor graft B). The red arrows at the bottom indicate the upward flow of sap, which can include chromatin masses from the lignified stem base. Species with relatively more lignin shed more chromatin masses and therefore may be more efficient for mentor grafting.

— successive grafting —

Another way to increase the variation rate is by successive grafting, or said another way, multi-generational mentor grafting. Seedlings grown out from a mentor grafted plant are screened for off-types, these variants are then mentor grafted, and so on. G1, G2, G3 is a way of notating the graft generation. A second letter is added to refer to subsequent non-grafted generations. G3Y5 would mean three successive generations of mentor grafting followed by five non-grafted. From the 1950s into the 21st century, Japanese researchers have studied graft transformation, mostly in peppers (Capsicum annuum). Yagishita (1961) observed that mentor grafting for successive generations strongly multiplies the rate of variants, confirming earlier findings by Glushchenko (source):

“the average rate of occurrence of plants bearing transformed fruits in G3Y1 and in G3Y2 is 10.7 times as much as that in G1Y1 and G1Y2.” This includes traits (such as fruit shape) transferred from across the graft as well as novel variation.

The transformation rate of the G1 seedlings averaged 6%. Grafting these successively for two more generations produced 10 times more variation at 64.4%. In tree crops this method can be still be practical as grafting seedlings onto older fruiting trees can shorten the juvenile phase to only a few years.

—hybridity—

According to Ivan Michurin, the developer of mentor grafting, using hybrid seed is essential. The studies on graft hybrids did not use hybrid seed, as researchers like to reduce variables to control the experiment. However, the successive grafting studies are the exception to this. In spite of being self pollinated, the seeds collected from the first generation of grafting (G1S1) are effectively hybrids. This increase in hybrid plasticity is why the transformation rate of the seedlings starts to climb steeply from 6% after the first graft generation to 64.45% by the third graft generation (G3). Besides hybridization, other kinds of genome shock can work similarly to induce plasticity for graft transformation, such as alien pollen shock, polyploid conversion, or viral infection. For example, Ohta and Chuong (1975) investigated effect of broad bean wilt virus infection on the transformation rate of mentor grafting in peppers (source). Mentor graft variant seedlings (G1S1) had a transformation rate of 16.5% with viral infection compared to 2.0% in the control group, an 8.25 times increase.

— mentoring the rootstock —

Nearly all of the studies on graft hybrids involve collecting seeds from the scion. Zu and Zhao also investigated the transformation rate of seed collected from the rootstock (source). On a 30cm tall white eggplant rootstock, they cleft grafted one purple eggplant at the apex, and side grafted another onto the main stem. They refer to this method as the double graft. It was arranged so that the white eggplant only had a single side branch growing in between two purple branches. Any other other side shoots emerging from the white eggplant were pruned off. Seedlings grown from the white eggplant fruit collected from this branch were 68.53% purple. Alongside this experiment, some white eggplant rootstocks were grafted with only a single purple eggplant scion at the apex, without the additional scion on the stem. In this case, the seedlings grown from fruit of the white eggplant had purple variants at a rate of 15.13%. Though still respectably efficient, it illustrates that the transformation rate is strongly negatively correlated to the amount of leaf biomass of the pupil plant. It may additionally indicate that the importance of having heterografts on either side of the stem from which seed is collected. Regardless, adding a second side graft to the main stem increased the variant rate of the seedlings by four and a half times. A 68.53% transformation efficiency appears to be the highest among the mentor grafting techniques that involve growing seeds. This figure depicts the fruits from the double graft experiment:

Figure 5 — Graft-induced variations in eggplant, in which 9-leaf eggplant was grafted onto white eggplant. First row: left: fruit of white eggplant; Right: fruit of 9-leaf eggplant; Middle: fruit in the stock of the immediate generation. Second row: Variant fruit in F1 generation. Third-Fifth row: Variant fruits in the F2 generation. (source, source)

This experiment was based on Michurin’s lesser known second mentor grafting technique where the pupil is the rootstock and the mentors are scions. Michurin recommended grafting scions from older fruiting varieties onto the crown and main stem of a young hybrid seedling, to simultaneously speed up its time to fruiting and mentor it in the direction of the scions. After some years of growing together, when the desired balance of traits has been achieved, the scions are pruned off.

— grafting flowers and fruit —

Grafting inflorescences and young fruit are also efficient methods of graft hybridization. Rajki and Pal (1966) grafted immature fruit from one eggplant cultivar onto another (source). Around 20% of the seedlings showed altered characteristics. This is consistent with the work of Glushchenko, who found that inflorescence grafting produced seeds with a relatively high transformation rate (source). Although these are mature parts of a plant, the young developing embryos are in a plastic state and forced to depend almost entirely on the substances from the rootstock. Inflorescence grafting has been developed in Arabidopsis by using a silicone tube to support and seal the graft (source). This should be an applicable technique for crops with inflorescences including the cabbage (Brassicaceae) and carrot (Apiaceae) families. Inflorescence grafting could be particularly useful for plants that are otherwise challenging to graft, such as those with a rosette growth pattern similar to Arabidopsis.

— genetic distance —

Recently (2024) a fascinating study in graft hybridization was published involving the grafting of grapevines onto Schisandra rootstocks (source). At the outset of this study a few decades ago, researchers were curious if the shared vining growth pattern of Schisandra and Vitis could be an indicator of graft compatibility despite the very large genetic distances. They also wanted to investigate whether grapes could be made to produce the primary medicinal components of Schisandra (they can). The transformed scions have grown for 25+ years. The authors notate this kind of graft hybrid as “Vs hybrids” (referring to both above and below the graft, as they both become transformed). The new phenotype is largely intermediate between the two species such as internode length and fruit color and so on, with some novel traits as well such as the palmate leaf vein branching pattern. The transformed phenotype was stable for all traits when propagated on its own roots.

This significant paper on distant interfamily grafting is the first to show a profound transformation of a stabilized scion, something that Michurin did not think was possible. In fact, none of the typical approaches to promote graft hybridization were used—a young seedling, a hybrid, pruning, etc. What would account for this? The conclusion of the researchers is that grafting across large genetic distances has a powerful transformative effect even on stabilized cultivars.

“Furthermore, interestingly, the farther is the phylogenic relationship of the species, the higher is the likelihood of HGT. This also explains why HGT caused by grafting of distant species can lead to the change in phenotypic traits…Therefore, creating new germplasms from grafting requires that varieties with large phenotypic differences and distant genetic relationships are selected to obtain the desired variation types.” (source)

“Leaf color, leaf shape, and stem color of S. chinensis in Vs hybrids exhibited obvious changes (Figure 1). This is likely the result of the combined effects of diverse genetic back-grounds, differential hormonal regulation, physiological conditions, and environment.” (source)

Michurin’s emphasized using distant hybrid seedlings for grafting, as their greater plasticity produces stronger results. This is somewhat analogous to large genetic distance between the rootstock and scion causing plasticity in a stable vegetatively propagated cultivar. The number of years the distant perennial graft develops is also partially analogous to the number of generations in successive mentor grafting. The authors of this study recommend experimenting with grafting morphologically (not so much phenotypically) similar but genetically distant plants. It’s also important to note that in this experiment the graft hybridization rate was 100% for all of the grafts that grew, making 23 new Vs graft hybrids. The transformation process occurred over several years, making the duration of time of the graft a key variable for this method.

Conclusion

With the appropriate technique, grafting can be a useful approach for many circumstances and goals in plant breeding. With just a basic heterograft, the seed collected from it tend to have hybrid vigor (source). Likewise, a standard intergeneric graft is able to cause heritable phenotypic changes in the seedlings (source). It’s helpful to consider combining multiple factors to maximize the degree of transformation. Michurin’s technique of grafting young hybrid seedlings and pruning their leaves is an example of this. Another example would be double grafting a young hybrid seedling with distant intergeneric scions. Using hybrid seed and wider genetic distance of the scion could in principle take the variation rate above 70% in the first generation of seedlings (G1S1), much better than the rate of a 1-5% found by some researchers. This grafted plant can be kept to alive for multiple seasons (in a frost free area if its tender) to keep increasing the variation level of its seedlings. Likewise, the process can also be repeated (successive grafting) to keep gaining variation, potentially with multiple different mentor species. When the desired pool of traits is obtained, recurrent selection can then be done to stabilize them, with no further grafting necessary.

Using large genetic distances to transform a graft, such as the Vs hybrids, is a novel area of investigation. There are likely many other distant combinations where long term graft compatibility can be achieved across large distances. Selecting for distant graft compatibility is potentially a powerful bridge to be able to gain many other new traits. Ways of extending distant graft compatibility, such as selecting universal inter-stems (aka graft adapters), will be important to make continued progress with this method of cultivar development.

On traits:
Graft transformation produces can produce two kinds of traits—those transferred horizontally across the graft and novel variation. Some researchers report that the traits inherit according to Mendelian rules, while others have reported that they do not. Often the variation will not appear until the second generation of self pollinated seedlings. Graft hybrid seedlings have frequently been found to display chimeric mosaicism, where variation occurs within a single plant, even a single branch. A fascinating observation about the traits from graft hybridization is that they can display broken linkage relationships (source). One problem that can arise when cross breeding is linkage drag, where an unwanted trait transmits together with a desired trait(s). Sometimes they are not able to be delinked with recurrent selection. Linkage drag is particularly prominent in crosses of crops with their wild relatives, making graft transformation a promising technique for these combinations, even where they can be crossed sexually.

Wide hybridization—the crossing of distantly related species—holds a lot of potential in plant breeding. Sometimes it’s only a matter of getting the timing right, making some pollinations, and growing out the seeds.

However it’s often more of a high hanging fruit situation, requiring painstaking work to get past crossing barriers. For the breeder, the extra effort may be rewarded with novel traits and adaptations. Luckily, these barriers can be flexible and susceptible to bypassing. Cement powder turns out to be one way of getting across some initial barriers, in particular fertilization and fruit formation. In the cacti growing community, people have been reporting success with cement since around 2012. In the Cactaceae family in particular, some species from different genera can hybridize readily, but in other distant combinations the flowers drop off soon after pollination. Using the “cement method” or “cement pollination,” several new intergeneric hybrids have been obtained in the cactus family. The basic technique: Apply a tiny of bit of cement powder to the stigma 30 minutes prior to the distant pollen (repeat the process). Experimenters have confirmed that other high pH powders such as CaCO3 can be used similarly.

Note: this technique can be used to break both self incompatibility and out-cross incompatibility. There are some shared mechanisms preventing both kinds of pollination, therefore some methods can break both kinds of incompatibility.

The original thread and instructions:

“1. Get yourself some Cement from the DIY Store. Very fine powder. The finer the better. But the typical Commercial grade works fine as well.

2. Get yourself a small brush and apply some of the cement dust on the Stigma of the flower on the plant that you want to produce seeds with. Also try to blow a little bit of the dust inside the flower.

3. Cement works as some kind of irritator that makes the flower create some Anti-Bodies that enable her to accept her own pollen.

4. Then wait for half an hour and brush some of the own pollen on the flower and repeat this numerous times.”

Pretty simple! A friend of mine at Urban Food Forest tested the cement method on shark fin melon (Cucurbita ficifolia) x watermelon (Citrullus lanatus) this season, and reported that with the cement method the ovaries (the base of the flower) began to develop and swell for a few days before the flower dropped. Without cement, the flowers didn’t show any sign of fertilization and dropped promptly the next day. This simple, cheap method deserves broad experimentation.

MSG to induce polyploidy. Another helpful household ingredient for the plant breeding toolkit is the umami food flavoring monosodium glutamate (msg). Msg has been recently used by researchers in India as a mutagen to generate polyploids and novel variation. Polyploidization, the doubling of chromosome number, is used in plant breeding for various purposes such as increasing stress tolerance, vigor, fertility, and plant size. As a result of this mutagenic process, novel variation also can appear. Polyploidization is a crucial tool in wide hybridization, used to restore fertility to sterile hybrids.

Photo of hybrid passionfruit seedlings: typical diploid leaf on the left, larger darker polyploid leaf on the right. These seedlings are all from the same seed parent, but the polyploid outgrew and out-flowered all the rest of the (~30) diploids. In this case the polyploid appeared spontaneously and not as a result of treatment.

One of the most commonly used chemicals use to induce polyploidy is oryzalin, a commercial herbicide. It’s therefore astounding that a food ingredient can also be used to generate polyploids. The ease of acquiring and handling msg opens the door for many more gardeners and independent plant breeders to experiment with it. There are many minor root and tuber crops for example where increasing their size would make a significant difference in the crop’s utility. Wild species can also benefit from this process, which can speed up selection and domestication.

Here is the protocol (source):

“Uniform sized fresh bulbs of Urginea indica Kunth (Fig. 2) were selected and their roots were removed completely  with scalpel. Five different concentrations of Monosodium Glutamate were prepared, viz. 0.1g/l, 0.2g/l, 0.3g/l, 0.4g/l and 0.5g/l. The bulbs were then soaked discretely in different concentrations of Monosodium Glutamate for six hours, subsequently the bulbs were washed carefully with running tap water for few minutes. Finally, the treated bulbs were planted in the prepared plots to raise M1 Generation.”

It’s interesting to note that more polyploids appeared in the second vegetative generation after soaking in msg (M2 vs M1). In this experiment, the lower concentration of .2g/l msg was the most successful in inducing polyploidy. Higher concentrations up to .5g/l were too mutagenic to efficiently generate polyploids. They end the paper with a discussion of the need to develop ideal msg concentrations for various different species. They subsequently made msg polyploids with another medicinal bulb Drimia indica (source). Protocols for the msg treatment of seeds and shoot tips should also be developed. Selecting out the polyploids generally involves looking for larger thicker leaves. Microscopes are used to count a more precise number of chromosomes. Sometimes recently converted polyploids are slower to get growing at the beginning, but they frequently end up outpacing diploids.

We have discussed some of the reasons to use polyploidy in breeding, such as restoring fertility to a newly created distant hybrid. The combination of polyploidy and hybridization is called allopolyploidy, which took place many times in crop domestications such as in sweet potato, wheat, peanut, quinoa, rutabaga and others. Another reason to generate polyploids that you may not hear about as much is to induce plasticity. The process of polyploidization, and strong stressors generally, cause genome shock to an organism. This can help a crop adapt to novel conditions, such as acclimatization to a new ecology. With continued cultivation and stabilization of the variety, plasticity will then decrease—the jumping genes are quieted into dormancy by epigenetic mechanisms. In the context of graft hybridization, plasticity is important because the genome instability promotes trait transfer from across the graft union. It may also help with increasing distant graft compatibility. The traditional recommendation has been to use hybrid seed for mentor grafting, again because of the genome instability. If for some reason hybrid seed isn’t able to be used, soaking seeds in msg could be an acceptable substitute. See this essay on for more information on the technique of graft hybridization.

Stay tuned for more discussions of simple DIY plant breeding techniques !

Most of the time grafting is done within a plant family, usually within a genus. There are old Chinese texts which talk about distant graft combinations, so it’s not surprising that Chinese researchers have been investigating distant interfamily grafting for crop improvement (source). They call this process “distant graft mutagenesis.” The technique, described in detail in the above link, involves plug grafting seedlings of a crop like soybean onto the base of a vegetable from a different family. As the scion grows it’s leaves are pruned, leaving only 2-3 at the apex. Seeds are collected from the scion, grown out, and screened for variants. The rootstocks are plants with thick stems or rhizomes/tubers. Interfamily grafts take longer to heal than more closely related grafts, but the success rate is surprisingly good for these virtually unrelated plants, with bizarre combinations such as wheat on sweet potato and soybean on ginger rootstock. Long term graft compatibility was not assessed in these experiments as they are annuals and only grow for a few months until the seed is collected. The results of these experiments are more or less mutagenic—the seedlings show a variety of new traits such as new seed colors, different growth habits, and even different chromosome numbers. This technique has been very useful generating new traits and has been applied to a multitude of crops for decades.

Photo: wheat growing on sweet potato (j), and mung bean on pumpkin (i):

In general with herbaceous plants, a graft healing chamber is required, with warm conditions and high humidity that gradually decreases over a 1.5-2 weeks. Keeping the young grafts in the dark for 24-48 hours in the beginning is also recommended. What do the distant graft mutagenesis (DGM) studies reveal about healing the graft unions of virtually unrelated plants?

1) Extend the time in the veggie graft healing chamber 2-3x
2) The scion, a young seedling, is plug grafted onto the stem base of a thick, succulent, or tuberous rootstock like sweet potato, ginger, or sunflower. If the stem base is vertical, its bent horizontally to send growth energy to the scion.

The table below shows the survival rate of soybean scions grown on rootstocks from different families. The average success rate is around 65%. Woody plant interfamily grafting is thought it be more difficult in general than non-woody plants. However, there are ancient Chinese accounts such as grapes on jujube, as well as a recent study of grape vines growing on shisandra rootstocks.

We can see from the DGM studies that forming graft unions across different plant families is to a great extent a matter of wound healing ability rather than just genetic similarity. This fact was highlighted recently with a Japanese study, the first of its kind to systematically look at graft compatibility, investigating combinations among 73 species across 38 families (source). They found that Nicotiana benthamiana has “the ability to graft virtually any plant family” (source). Nicotiana benthamiana is able to do so because it produces an enzyme (1,4 beta-glucanase) that promotes the healing of graft unions and wounds generally. The authors of the study were able to use this species as a universal interstem/intersection to connect rootstocks and scions from different plant families, such as tomato on Chrysanthemum. "Using Nicotiana as an intermediate, we also achieved other grafts in which the scion, interscion, and rootstock all belonged to different plant families (source).”

This research group more recently found that Petunia x hybrida also has this same ability to form interfamily grafts with relative ease (source). Here is a table of the different families that they were able to graft Petunia to. The authors suggest searching for other species within the nightshade family that may also have this ability. While grafting this spring, I noticed that Physalis longifolia has an ability to heal graft unions rather quickly even under stress, so might also function as a universal interstem, also called a “graft adapter.” These or other nightshade species should be investigated for the ability to graft woody plants together. Perhaps a cold hardy species such as goji (Lycium) could be used or otherwise the interstem may be able to gain some cold hardiness from the molecules and endophytes of the woody plants.

One other way to extend graft compatibility is by using hybrid seed, particularly distant hybrids. This is a phenomenon that Ivan Michurin wrote about. One of his assistants grafted a 1 year old lemon onto a 1 year old hybrid pear seedling, and the pear subsequently became evergreen like the lemon tree. Michurin recommended distant hybrid seedlings to be used for distant graft experiments. Perhaps this ability of hybrid seedlings is related to faster growth rate, better wound healing ability, or just greater cellular flexibility.

Let’s go over some of the reasons for distant grafting that have been studied. It can be a form of mutagenesis and produce novel traits, as the dozens of patents and cultivars developed in China show (source). It can give a crop such as tomato the ability to grow on the unrelated Chrysanthemum, “one of the most prolific plants on land (source).” Another reason is to graft two species prior to crossing them. In 2015, a Chinese study was published showing a successful crossing of goji (Lycium) and pepper (Capsicum) (source). This study reveals that prior grafting can make even very distant inter generic crosses feasible. Perhaps even a cross between two closely related plant families could be achieved this way? Even without sexual crossing, grafting plants from different families that are woody perennials (or at least long-lived in a greenhouse) has been shown after some years to act as a powerful transformative force on the scion (source).

Hopefully many new research directions will be taken to keep advancing our knowledge of distant grafting. As a low-tech method, its a great area for amateur researchers make contributions in.

Dioscorea polystachya — Pretty much the only crop in the yam family (Dioscoreaceae) for cold climates. Human relationship with this species goes back at least 30,000 years (source). This yam is one of the lowest effort starches in this climate, which is analogous it the Asian climates where it’s from. It fills a special niche for being like a self expanding perennial potato. Despite it being fairly rampant in some conditions such as mountain roadsides, in the right context its not hard to manage here. This year there was a period of strong heat/drought, which led to the deer eating the leaves repeatedly and taking out most of the seed crop. Outside of Asia, there aren’t many working with improved cultivars of this species, much less growing from seed. This project is in the early stages of botanical seed growing. The goal is to select easy to harvest cultivars from true seed that have improved fertility. There is diversity of starch type and texture among cultivars, as well as a few different root shapes.

Cucurbita lundelliana x ficifolia — The quest to make a super adaptable squash hybrid that can also function as a genetic bridge is going well so far. The F1s are growing strong and about to flower. They look 98% like the seed parent. In this case it’s likely from two combined factors: maternal dominance and wild dominance. The F1s are therefore very bitter like the wild species C. lundelliana (you can tell just by tasting the leaves). In the coming weeks I’ll begin to make crosses back to the domestic species C. ficifolia. The blending of these species should produce a wide range of climate tolerance as well as insect and disease resistances. This makes these F1s very exciting as a genetic starting point for a broad range of very resilient new cultivars. These multi resistances can be taken in many directions and brought into additional species like C. moschata, maxima, and pepo—which can all be crossed or bridged into lundelliana without much fertility loss.

Nearly all of the F1 seedlings are like the highly lobed seedling below, which is to say exactly like the wild seed parent. Only a couple have the more domestic, less-lobed look of the vine at the top.

Goji hybrids (Lycium barbarum, ruthenicum, and chinense) — The goji hybrids are growing well, especially once they size up in a sunnier microclimate. Goji berry is an easy to grow, multi use crop, but as a high desert species is not well adapted to this humid climate. Most cultivars have a bittersweet flavor, which mellows when dried. The leaf goji L. chinense has better adaptation to humid climates, but has smaller, more bitter berries, a shorter flowering time, and longer seed to seed cycle. But, it does have large tasty leaves. The seedlings I’m growing are (black goji x yellow goji) x leaf goji. Growing pure barbarum from seed in this climate has yielded low vigor seedlings. Goals include fungal tolerance, fresh berry flavor, clumping habit, vigor and tasty leaves.

Passiflora hybrids (P. incarnata, edulis, flavicarpa, cincinnata, caerulea, tucumanensis, phoenecia) — A big attraction of working in this genus is the near zero effort required in growing beautiful flowers and tasty fruit. All the seedlings I grow have the freeze tolerant P. incarnata to one degree or another. The main negatives of this species is the aftertaste of the seed and somewhat over-expansiveness of the rhizomes. The hybrids have a variety of selectable characters: fertility, flavor, size/expansiveness, precocity, etc. The main goals are fuller juicy fruit, different flavors, clumping roots, and less aftertaste in the seeds. Other possible directions are thicker peel from the species Passiflora phoenecia, which can be used as a vegetable. A new group of complex hybrid seedlings will mature fruit this year, some of which should have juicy orange arils and low acidity like the seed parent.

Helianthus tuberosus Rode x Dwarf — This wasn’t a crop I had planned on working much on, but these seedlings revealed themselves in the garden this spring. Dwarf is a super short cultivar, under two feet tall, but it doesn’t easily flower or produce seedlings. Using it to develop new short, clumping cultivars that have improved flowering seems worth pursuing. Helianthus has a nice effect of reducing grass growth, which can be helpful in polycultures particularly when the plants don’t get super tall and wide. I likewise prefer smaller size tubers that can be cooked whole, as opposed to the large knobby shape of some types. Another interesting route is the potential for Helianthus tuberosus to be able to cross with other genera in the family (source). H. tuberosus is among the most reliable, low effort perennial crops.

Polygonatum (P. huanum, darisii, biflorum, sibiricum, martinii, macranthum) — Huang Jing/Solomon’s seals. They are relatively slow growing understory or forest edge species. There are many species, with the center of diversity in China. They are used medicinally, as well as in soups and also in various functional food products (source). I have a group of some 15 hybrid seedlings of P. darisii x huanum. These are proving to be vigorous and beautiful. Darisii is a hard to find species with large potato like rhizomes up to 1kg. Another beautiful species with large rhizomes is P. martinii, closely related to P. cyrtonema which is cultivated for the production of the medicine “huang jing”. Another species used to make huang jing that I grow is P. sibiricum, which is used a staple food as well as a medicine, sometimes called “Siberian ginseng.” I also grow the native species P. biflorum. I plan to only collect seed from the species that germinate after one winter (instead of two), in order to speed up selection. This means collecting seed from the whorled leaf species (Sect. Verticilliata), but the pollen parents can be very distant. These have great potential for nutraceutical production, and are highly ornamental. Goals are large rhizomes, later sprouting shoots, ornamental traits, and improved flavor / ease of processing.

Last year I started an OP tomatillo landrace with Chupon de Malinalco, Tiny from Coban, and a commercial green type. The F1s have been crossing themselves this year. I also began a Cynara landrace with 3 artichokes and 3 cardoon cultivars, which are currently maturing seed. Other grexes I’m saving seed from this year are ‘Ultracross Okra’ and ‘Homesteader’s Kaleidoscopic Perennial Kale’ both of which are very vigorous and fun to grow.

I will do another project snapshot in the fall, including a list of failed attempts from the year.

Continuing the theme of plasticity in breeding, let’s explore another way of activating transposons. The overarching idea with this type of breeding is to apply certain stressors at sensitive phases of development. Transposons cause mutations and alter phenotypes, in fact many domesticated traits relate to transposons.

A fascinating and simple way to achieve this is with alien pollen. Alien pollen in this sense is incompatible, meaning it does not successfully fertilize the flower. It’s therefore necessary to do a second pollination with a compatible pollen, which can be either selfing or crossing. This is a type of repeat pollination, pollinating the same flower at two different times. The incompatible alien pollen is applied early, either in the bud stage or right when the flower opens. Then, at the end of the flower’s window of receptivity, you apply the compatible pollen. The alien pollen source can be relative in the same family, or even a virtually unrelated plant from another family (source). This stress is thought to be caused by small molecules and siRNAs from the pollen entering into the cells of the stigma.

I first read about this phenomenon in an old abstract where they injected paper mulberry pollen into a developing fig. This caused the fig to clone itself via seed, a process called apomixis or gynogenesis. In this case there was no second application of pollen needed, since the plant cloned itself through seed. But despite being clonal, the seedlings showed variation. I wanted to learn more, but the full study wasn’t available, so I looked for others.

A 2014 study investigating this phenomenon used wild rice (Zizania) pollen on cultivated rice (Oryza). It can be read in full here: Mobilization of Diverse Transposable Elements in Rice Induced by Alien Pollination Without Entailing Genetic Introgression. Using this technique the authors were able to select new and improved lines:

“alien pollen may produce a kind of ‘biological stress’ that can induce genome variations… This process could be used to generate genetic diversity in crops, as demonstrated by the increased plant height and enlarged seed size in the X9 line.”

This study followed on a previous one that applied pollen from the virtually unrelated plant evening primrose (Oenothera biennis) to rice. That study can be read in full here. Using the very distant interfamily pollen from evening primrose generated a mutator phenotype that “produces transgenerational genetic and phenotypic variations, including mobilization of several TEs (source)”.

After ruling out other mechanisms, the authors believe that the stress is caused by small signaling molecules and sRNAs that enter into the recipient’s stigma cells:

“although pollen tube of Zizania were incapable of extending and hence the fertilization was blocked, some substances (e.g., signaling molecules and small RNAs) can be released and brought into the zygote upon subsequent self-pollination of the rice”

The authors suggest trying this with plants from the same family but that aren’t cross-fertile. However, the earlier study shows that it also can potentially work with interfamily pollen. The most effective way would be to use a pollen mix, combining a multitude of incompatible pollens. Hybridizers often apply a mix of marginally compatible pollens to increase the changes of successful crossing, which is said to have a synergistic effect. Likewise with an alien pollen mix, the greater amount of small signaling molecules taken up by the zygote could potentially activate a wider range of transposons, leading to greater variation. It’s also likely, particularly with related pollens in the same plant family, that endophytes are being transferred into the cells of the stigma along with the other small molecules.

Let’s imagine one such experiment. Say you are going to make a wide cross between two species of tomatoes such as Solanum lycopersicum x habrochaites. In addition to the habrochaites pollen, you have prepared an alien pollen mix consisting of tomatillo, eggplant and pepper pollens. In the bud stage you open up the domestic tomato (lycopersicum) flower and apply the incompatible pollen mix. After several hours up to a couple days (depending in the flower’s receptivity window), you apply the Solanum habrochaites pollen. Of course, it’s not necessary to combine this technique with wide crossing, but there are reasons one might do so. Distant crossing plus alien pollination can in principle lead to an even greater range of plasticity and variation on the seedlings. Also, inducing plasticity in the zygote cells prior to applying marginally compatible pollen might increase the success of distant hybridization (as in the above example with tomatoes). Other reasons to leverage increased plasticity, such as in mentor grafting, are discussed in the post Grafted Realities.

Alien pollen shock can likewise be combined with other methods in the pollination stage, such as pollen mixes, mentor pollination, pollen treatments, stigma treatment, and so on.

The authors of the study conclude that like hybridization in nature, alien pollination is another natural source of genetic variation:

“It is conceivable that ‘accidental’ pollinations may occur under natural settings, where alien pollen of related species are sympatric. Therefore, our observations suggest that alien pollination may be one cause of natural genetic variation, particularly when TE mobility is involved.” (source)

Stay tuned for more discussions on evolutionarily catalytic techniques and processes related to plant breeding!

Did the plant breeder known as the 'Italian Michurin' develop a relatively safe, DIY method of pollen irradiation using magnetic fields?

In the process of looking at references on Michurin, I came across the name Alberto Pirovano (1884-1973). Pirovano was the son of a grape breeder and a self taught electrical experimenter. He released several grape cultivars cultivars which are still grown widely such as ‘Italia’ used in pisco production in Peru (source). He was an early pioneer in the field of mutation breeding, among the first wave of experimenters to apply electromagnetic fields to seeds and pollen in the in the 19-teens and twenties prior to the burgeoning of mutation breeding as a field (source).

What similarities did Pirovano have to become known as the “Italian Michurin?” Like Michurin, his research interests had to do with “the plasticity of species,” but he did not work with grafting (source). Like Michurin, Pirovano also claimed that exposing pollen to electromagnetic fields promotes the success of distant hybridization, but Michurin used electrostatic fields for this purpose (source). Like Michurin, a version of his ideas were adopted by the fascist regime of his country and became associated with “Lysenkoism” (source). Could there have been a baby lost in the bathwater of politicized science as with Michurin? While Pirovano’s theories of heredity and electrogenetics can be largely dismissed in light of modern biology, what can be learned from the plant breeder who spent decades treating pollen and growing out the seeds?

Pirovano published a 300 page text in 1922 called the “Electric mutation of botanical species.” Later in the 60s it was translated to English and published as “the Electrogenetics of Alberto Pirovano” but didn’t remain in print long.  The original Italian version of the text is available online. It’s written in a form of Italian that is cumbersome for native Italian speakers today. It includes about 100 diagrams of machines that Pirovano built for pollen treatment.

In 1925, Flint published a critical review of Pirvano’s book in English in the Journal of Heredity (source). Here are some relevant sections:

“These methods are all homogenous in that they all involve the electrical treatment of pollen prior to pollination yet they offer a lamentable diversity in the particular nature of the electrical treatment, since use is made of radio-active materials, x-rays, ultra-violet rays, electrolytic action, magnetism and high tension electric current, with diverse variations and combinations.”

The criticisms of Pirovano are primarily due to his not having done properly experimentally controlled trials, using multiple variables at once. The other criticism is that the variation Pirovano observed could be part of the normal range of variation of a species, or a result of hybridization. Flint continues:

“…the types of variation obtained, and attributed by Pirovano to the influence of the electrical agencies, are of the sort ordinarily associated with hybridization, while the frequency of these variations is not clearly established as having been modified…The plants used in these experiments were all annuals, and included species of Papaver, Cheiranthus, Helianthus, Althea, Cucurbita, Lunaria, Solanum, Brassica, and Pisum. No experimental data for any of these plants appears sufficiently convincing to establish the fact of abnormal variation, let alone the definite association of such variations with electrical influences.” (source)

All of these same criticisms of Pirovano are rehashed in 21st century references such in the 2017 book “The Lysenko Controversy as a Global Phenomenon: Vol II” (source). A few paragraphs from Flint’s 1925 review made their way into that book, including this part:

“Pirovano’s data and illustrations were therefore misleading since they failed to indicate the true range of variability associated with the use of normal pollen. Furthermore, the types of variation obtained—and attributed to the influence of experimental treatments—were of the sort ordinarily associated with hybridization, and there were no data on the changes in the frequency of these variations under experimental conditions.”

The above section is not cited as Flint’s conclusion, and reads as the conclusion of the authors. There probably isn’t much to take issue with regarding the lack of experimental control or the dismissal of electrogenetic theory. What strikes me as odd and inconsistent, however, is to say that all of the phenotypic variation that Pirovano observed was natural variation. Pirovano frequently exposed pollen to multiple sources of irradiation as Flint notes, but did so because he was more interested in induced plasticity than teasing out the specific effects of field type and intensity for each species. Flint can’t be faulted for assuming the possibility that all of the variation that Pirovano witnessed was due to already existing or to hybrid variation, because mutation breeding as a field did not exist in 1925. It wasn’t until the ensuing decades of the 30s-60s that mutation breeding as a field really took off. Since mutation breeding has become widely known, the criticism that Pirovano was working with natural variation would not seem to make as much sense as it did in 1925. Pirovano spent several decades exposing pollen to a huge range of electromagnetic fields, including ionizing radiation.

“First, Pirovano combined different kinds of electrical treatment—radioactive materials, X-rays, UV rays, electrolytic action, magnetism and high-tension electric current without specifying the alleged mutagen agent (source).”

How is it possible in 2017 to criticize Pirovano for using too many variables at once— including intense ones like X-rays and radioactive materials—and in the previous paragraph say that he wasn’t inducing any novel variation just working with naturally occurring variation?

Pirovano’s last publication that I could find is a short article from 1950 called “The Institute of Fruit-culture and Electrogenetics in Rome” (source). It was translated into English, indeed it’s the only writing by Pirovano in English that I have seen. By this time, Pirovano was approaching five decades of work, and for the last two of those the field of mutation breeding as a field had been developing internationally. The theory of electrogenetics however had not been developing alongside mutation breeding, and electrogenetics stopped being a term of use. The 1950 article depicts some of the variation that Pirovano achieved:

Pirovano published his book on electric mutation in 1922. In 1927 the Institute of Electrogenetics and Fruit-culture was formed in Rome. Nearly 30 years later the institute published an article summarizing their work. Its possible that the criticisms regarding a lack of experimental controls in by commentators such as Flint in 1925 caused Pirovano to make more careful experimental designs in his ensuing decades of work at the Institute of Fruit-culture and Electrogenetics. The 1950 article depicts some interesting variation, but by far the most interesting thing was Pirovano’s excitement about the effects strong alternating magnetic fields on pollen. Pirovano was already discussing the magnetic field treatment of pollen, in addition to ionizing radiation, in his 1922 book on electric mutation. Yet the field of mutation breeding subsequently developed around the use of only the ionizing forms of radiation such x-rays and gamma rays (chemical mutagens are also used). Ionizing radiation directly damages DNA, but magnetic fields (even fairly intense alternating ones) are non-ionizing. By the time of the 1950 article, pollen treatment with ionizing radiation was well known by scientists and in use for some time. Indeed, we still use it today, yet magnetic field treatment of pollen is unheard of. Is the reason simply because ionizing radiation damages DNA and therefore works, while magnetic treatment does not, so was forgotten? Perhaps, but why after 4+ decades of work did Pirovano still insist that magnetic irradiation was more useful (source), while other methods he worked with became commonplace? According to Pirovano, magnetic irradiation is more forgiving, it doesn’t reduce pollen viability as ionizing radiation can, but also because it promotes the likelihood of distant hybridization. With ionizing radiation, the proper strength to induce variation and not kill the pollen is a narrow window. Also, a person can do magnetic irradiation at home but ionizing methods would be more difficult and require more safety precaution.

After looking at this 1950 article, I found the link for Pirovano’s book in Italian. It’s interesting to scroll through and look at the diagrams but you can’t get much out of it, and an old copy of the English translation currently sells for around 1000$. I sent the link of Pirovano’s book to a friend of mine in Italy named Paolo who is a plant breeder as well as electronics experimenter. He got back to me a couple weeks later, saying it was a difficult form of Italian to understand, but he had made it through the book. Paolo stated that the most salient thing to him was the use of fairly strong rapidly-alternating magnetic fields to irradiate pollen. Paolo described to me how to replicate Pirovano’s magnetic irradiation setup with a greater efficiency using modern methods. Fairly intense variable magnetic fields ranging in frequency from 10s-100s Hz are required to replicate the magnetic irradiation experiments. It is most easily achieved using a spinning rotor containing neodymium magnets of alternating polarities. Something akin to this:

Is Pirovano’s magnetic irradiation legit? Until someone replicates it, we can’t say for sure. The threads of the case merit pulling on, but until then, is there anything in the scientific literature indicating a potential for magnetic fields to induce genome instability or transposon activity?

Here is one interesting reference:

“The research group was the first in the world to describe genomic instability caused by an extremely low-frequency magnetic field, and this can be regarded as their most significant achievement so far. Genomic instability is a phenomenon that was first observed under ionising radiation, changing our understanding of the basic concepts of radiation biology. According to traditional radiation biology, possible mutations in a cell exposed to radiation are inherited by future generations of cells as such…However, more recent observations in radiation biology show that offspring cells inherit an increased tendency for mutations, meaning that there will be genetic variation in future generations of cells. This phenomenon is known as genomic instability, and recent findings now show that it can also be caused by extremely low-frequency magnetic fields.” (source)

Pirovano’s thinking, as written about in "The Lysenko Controversy as a Global Phenomenon Vol. II,” was that the electromagnetic field treatment of pollen functioned to “shake the stable arrangement of atoms” and thus mutate the resulting plant:

“According to Pirovano, the stability of the species could only be explained by the stability in the molecular structure of the germplasm. A direct action could thus bring disorder (and variation) in the atomic composition of the plasm. This action, which he called jonolisi, consisted in the application of a variable electromagnetic field directly to the pollen. The jonolisi was supposed to shake the stable arrangement of atoms, if the result was one of the few life-compatible, to give birth to a mutated plant.”

The destabilization of the organism can of course be caused by DNA damage in the case of ionizing radiation. In the case of magnetic irradiation, the induced plasticity can potentially occur due to the mobilization of transposons in the pollen, a less direct way of altering the genetic structure. Pollen is inherently more susceptible to this as it “undergoes dynamic epigenetic regulation of expression from transposable elements” and “growing evidence indicates expression of TEs (transposable elements) is more dynamic in pollen than other tissues” (source). Perhaps the magnetic irradiation of pollen is a legit technique and does in fact result in the plasticity that Pirovano was so focused on?

*Some other sources:

• Magnetic Field Exposure Stimulates Transposition through the Induction of DnaK/J Synthesis (source)

• Genomic instability induced by 50 Hz magnetic fields is a dynamically evolving process not blocked by antioxidant treatment (source)

• Evidence of Changes in Genomic Location of Transposable Elements in Drosophila Melanogaster Flies Exposed to Static Magnetic Fields (source)

One thing plant breeders do is apply selection pressure. Selection pressure is thought of as the external forces acting on an organism that affect its survival, such as predation, resource competition, pathogen exposure, heat or cold, and so on. Human-mediated selection pressure, Darwin referred to as artificial selection. Judgements like “this plant is too spiny, so I’ll cut it down” or “this fruit is sweet, so I’ll spread the seeds”, and so on. Joseph Lofthouse, author of the excellent book Landrace Gardening, feels that 85% of selection is done by the ecosystem.  The other 15% is the space for directed breeding work aka artificial selection. What would plant breeding look like from the process-oriented, “topsy-turvy” view of ecology ?

The systems ecologist Dr. Robert Ulanowicz uses the ecological concept of autocatalysis as didactic entry point into this view. A simple depiction of autocatalysis is the interaction of the elements A, B, and C in a loop.  Any change causing an increase in one element ripples through the network and back on itself, causing more and more resources to be pulled into the system. This reveals a level of selection pressure acting top-down through network feedback dynamics.  These networks are very common in ecology.

“Autocatalysis is capable of exerting selection pressure upon its ever-changing, malleable constituents.” - Dr. Robert Ulanowicz (source)

We are taught not to think using circular logic. Deductive reasoning is the gold standard, while circularity synonymous with nonsense. Yet if we abandon circular causation completely, we only see the mechanical subsets of living systems, overlooking the non-mechanical behaviors they exhibit.  In terms of selection pressure, the conventional emphasis is on linear, individual-based, and competition-driven processes.  The ecological perspective integrates this with broader non linear, network-based, cooperative dynamics.

Plant breeding influenced by ecological thinking places a greater focus on growth and development at multiple scales. This can apply to the level of the genome, the landscape and the ecosystem. It can mean breeding for polycultures, agroforestry systems, and ecosystem services. It can involve adaptive management, community engagement, and the holistic evaluation of traits. It might even mean selecting for emergent properties that we hadn’t foreseen.

Let’s take a look at how living systems grow and develop through autocatalysis (source). The representation below compares a young system A to an older version of the system B.

We notice right away that there are many more connections in the original system A compared to the more streamlined configuration of B. Many connections are pruned away in the development from A to B, yet the total amount of material and energy throughput is increased, as indicated by the thicker arrows. At the level of the brain, it represents the changes from a child to an adult. For a plant, it’s a young seedling compared to an older flowering plant. At the level of the ecosystem, this represents what we call succession. As ecosystems climb this developmental curve, there is a sweet spot they tend to hover around, having to do with the trade-off between resiliency (or diversity) and overall productivity (or efficiency). From time to time, the system gets challenged by what ecologists call perturbations. External shocks occasionally disrupt the system, causing it to reset to an earlier developmental phase. The stronger the stress, the further the reset goes back in developmental time, resembling to a greater degree system A. In a terrestrial ecosystem, this results in the proliferation of early succession plants that we colloquially call weeds. A stronger perturbation can set succession back even further to lichens. Whereas an old growth forest is networked like system B—productive, robust, with relatively stable and determinant flows.

When we prune a plant, it sends out new green shoots. Before sending out new shoots, it forms a layer to heal the wound called callus tissue. The callus tissue is sort of like an undifferentiated blob of gel. As the counterpart to stem cells in animals, callus has the potential to develop into any kind of plant tissue. Callus tissue is also formed when plants heal graft unions. Callus tissue has very high plasticity, just like system A in the schematic above. In fact, sometimes simply pruning a shoot can cause a doubling of the genome, or polyploidy (source). Variation of chromosome numbers is found naturally in callus tissue, an indicator of its high plasticity. A plant that is flowering is on the other end of the spectrum like system B.

Callus tissue also forms when growing plants in tissue culture. The cytogeneticist Barbara McClintock received a Nobel prize in 1983 for the discovery of transposons. Transposons are the cellular mediators of plasticity (system A), and activate after stress. The title of McClintock’s Nobel speech is called The Significance of Responses of the Genome to Challenge. Various synonyms are used for challenges to a system: stress, disturbance, perturbation. Another term that McClintock used is shock, known as her “genomic shock hypothesis.” In the Nobel speech, McClintock talks about the novel mutations that arise from growing out tissue cultured corn plants. The title of the speech hints that there’s a deeper significance of the responses to genome shock than we had realized. The significance has continued to reveal itself as scientists have gradually ditched the term “junk DNA” to refer to transposons. There has been an increasing realization is that transposons play an important role in genome regulation and contribute to evolutionary processes. When an organism is more developed (as in system B), transposons are inactive, kept silent by epigenetic mechanisms. But when a challenge arises for the organism, the transposons mobilize. They jump around the genome, cut- and copy-pasting themselves, hence the name “jumping genes.” They have also been called the “weeds of the genome.” By the ecological definition of a weed, it’s an accurate metaphor in that they come out of hiding and proliferate after disturbances. Weeds can also direct the system into different future states, as transposons do with the genome. Weeds sometimes spread to new ecosystems, through close contact or over larger distances via an intermediary such as a bird. Likewise, transposons can spread into new genomes, through close contact or via an intermediary such as a virus.

The notion of graft hybridization first appears in old Chinese texts. There are many examples of grafting distantly related plants for their combined qualities. For example, there is the recommendation to graft pear onto jujube to produce the best flavored pears. In the West there has traditionally been much skepticism toward graft hybrids. One reason for this is that some researchers early on didn’t apply the proper methods to maximize the chances of success. Under the normal technique of graft propagation these effects go unnoticed to a large extent. In 1907, German botanist Hans Winkler demonstrated that you can create graft chimeras by grafting then making a cut at the graft union. Occasionally a chimeric shoot arises from the graft union. It consists of a combination of two different types of cells growing together, which in their most harmonious pattern occupy adjacent layers like a hand in glove (a periclinal chimera). They form a unit, but are able to be separated again. After Winkler demonstrated the nature of graft chimeras, for many people this settled the question of graft hybrids. They decided graft chimeras must be the sole phenomenon responsible for the graft hybrid debate, and indeed this is still a prevalent view today among horticulturists and plant breeder (source). There is some irony to this, as Winkler himself was not convinced this was the case. Winkler saw clearly that there were 3 theoretically possible types of graft hybrids: 1) fusion hybrids 2) influenced hybrids and 3) chimeras. In one of his experiments synthesizing graft chimeras, Winkler found a polyploid shoot coming out of a graft union that did not appear to be a chimera, but a cell fusion hybrid between the two species. This plant unfortunately died before it could be propagated out to other researchers, and with the same wave of the hand, many commentators brushed this off also as a probable chimera (source). Nearly a century later in 2014, cell fusion hybrids were selected out from the graft union of two different Nicotiana species, see Horizontal genome transfer as an asexual path to the formation of new species. Winkler’s cell fusion hybrids at the graft union have now been confirmed and created experimentally along with graft chimeras.

So what about the “influenced” graft hybrids? Winkler only noted the theoretical possibility of these, but his experimental method could not produce them, so he remained agnostic about their existence. Unlike chimeras or cell fusion hybrids, influenced graft hybrids do not arise from a shoot at the graft union. Ivan Michurin developed a technique to produce influenced graft hybrids called the mentor graft. Here is a depiction, from the study “Hereditary changes in Capsicum annuum LI Induced by ordinary grafting.”

The technique is to graft a young hybrid seedling onto older rootstock, then while it grows prune all but the 2-3 leaves at the scion’s tip. In this way the scion (and its seedlings) will be “influenced” (or mentored as Michurin called it), with an increasing intensity over time, by a mostly one-directional flow from the rootstock. Like the other types graft hybrids, influenced graft hybrids have likewise been confirmed in the literature (e.g. Molecular mechanism of graft transformation in Capsicum annuum), but unlike the other two types these still elicit incredulity. In fact, there are more than two dozen studies confirming these graft hybrids (including a few showing genetic influence across the layers of chimeras). These studies frequently use Michurin’s mentor grafting technique but not always. There is some variation in the experimental designs as well as kinds/intensity of effects. These experiments are typically set up so that the trait transfer is obvious to notice, such as a green leaf scion growing on a purple leaf rootstock, or a jalapeño pepper on a bell pepper rootstock*.

Mentor grafting is about affecting an increased flow from an older, larger, stabilized plant (system B) into a new, small, plastic seedling (system A). Stressful conditions combine in the young organism, which mobilize transposons. Spreading around the genome they disrupt genes, create new regulatory networks, and introduce new traits by causing mutations, gene duplications, and chromosome rearrangements. Additionally, in the context of a mentor graft, transposons can promote horizontal genetic transfer through the genome instability and repair mechanisms they trigger. You could reason autocatalytic loops at play in this situation, for example foreign genetic material (such as RNAs) activate transposons in the scion, the resulting genomic instability promotes the uptake of foreign genetic material, which then continues to activate transposons. The leaf pruning stress of the scion further engages types of these loops, for example by increasing extracellular vesicle production, transport and uptake. This is like a chaos theory approach to plant breeding: a new system with unstable initial conditions is fitted within the highly perturbative flows of a large attractor. The intensity and the type of these conditions can be varied to affect the results. In some experimental conditions, the variation does not show up until seed of the scion are grown.

Applying the ecological view to plant breeding and development can be taken in two directions. One direction is taking plant selection out into multiple layers of the ecology and the community to benefit both. The other direction is toward an ecology of the genome, applying disturbance regimes and nurturing new developmental pathways for organism similar to the management of the wider ecosystem. Working with disturbance regimes and directing development on both of these levels holds great potential for synergistic interactions. Returning to the ideas of selection pressure and autocatalysis, they can also form a loop. In the context of a mentor graft, diverse foreign biomolecules flood into the scion in a sustained way. These stress conditions are a form of selection pressure, one which not only acts to select among the existing diversity, but also reconfigures the existing diversity, and is source of new diversity. This is essentially applying autocatalysis to selection pressure. As chain reactions take place, the more dynamic the results can be. This dynamic form of selection pressure could be referred to as evolutionary catalysis, capturing the ideas of rapid trait development and an increased genetic pool.

Regarding the kinds of molecules that move across the graft union, there are many: “macromolecules such as proteins and hormones, as well as small signaling molecules such as sRNAs and miRNAs, can be exchanged. Further, cpDNA undergoes genetic material exchange, and horizontal transfer of nuclear genes occurs at the graft union” (source). What’s more, even molecules that have been considered too large to move across the graft union such as chromatin masses have been shown to do so, enhanced by the technique of pruning the scion leaves (source). Chromatin is a relatively large and complex macromolecule consisting of DNA, RNA, and protein.

The ability of chromatin to travel suggests that other large biomolecules, such as proteins, large RNAs, and even organelles, might also translocate under similar stress conditions. Stress conditions are able to increase the permeability of the graft union and dilate the pathways that these molecules move thorough. These conditions promote the horizontal transfer of epigenetic modifications, genetic material, microbes, and other information. We might characterize a graft hybrid as a horizontally integrative organism.

The photo below shows a graft hybrid of a grapevine grown on the very distantly related Shisandra rootstock (source). G is the original unmodified green grape cultivar, while H is the same cultivar after growing and transforming for several years on Shisandra rootstock. The grapes became much darker and closer in color to shisandra berries, and they also now contain the medicinal components from shisandra. All of the traits stabilized, even when the Vs (Vitis on Shisandra) was grown out later on its own roots.

Stay tuned for more thoughts on symbiogenic and process-oriented approaches to plant breeding.

*some of the studies done on influenced graft hybrids:

• Strou, M. et al. 1963. Modifications transmitted to the offspring, provoked by heterograft in Solanum melongena.

• Tsaballa, A. et al. (2013). Molecular studies of inheritable induced changes in pepper (Capsicum annuum) fruit shape.

• Zhang, S. et al. (2024). Interfamily Grafted Hybrids Vitis vinifera/Schisandra chinensis Resulted in Transcriptomic, Phenotypic, and Metabolic Changes

• Li, J. et al. (2013). Heritable variation and small RNAs in the progeny of chimeras of Brassica juncae and Brassica oleraceae.

• Hirata, Y. et. al. (1994). Genetic constitution of germ cells in intervarietal and interspecific chimeras of Brassica induced by in-vitro grafting

• Pan Xiang-wen, et al. (2012).  Optimization of Distant Graft Mutagenesis Technology in Soybean

• Zhou, X. et al (2013). Confirmation of a purple-leaved plum graft hybrid.

• Frankel, R. (1962). Further evidence on graft induced transmission to progeny of cytoplasmic male sterility in Petunia.

• Yagishita, N., & Hirata, Y. (1987). Graft-induced change in fruit shape in Capsicum annuum LI genetic analysis by crossing.

• Yagashita, N. and Y. Hirata, 1984. Genetic analysis of new cultivar obtained by grafting in Capsicum annuum

• Hirata, Y. (1980). Graft-induced changes in eggplant (Solanum melongena L.), 2: Changes of fruit color and fruit shape in the grafted scions and in the progenies from the grafted scions.

I decided to read Michurin’s book ‘Selected Works.’  After getting past a few pages of propaganda in the introduction, I found it an earnest account of his experiences over the decades.  One reason you get this impression is that there seems to be a kind intuitive logic to what he’s saying.  Caveat: what you see written about in the cold war biology debates as “Michurinism” is bit of a different beast, and was developed in large part through the writings and edicts of Trofim Lysenko.  You can get a feel for the difference between Michurin and Michurinism by doing image searches of Michurin and Lysenko, you’ll see what I mean. One big difference is that Michurin did not deny the existence of discrete units of heredity and Lysenko did.  This is part of the debate that went on at the time before the existence of DNA had been demonstrated.  While the Soviet government did much to support Michurin later in his life, it was only about the last decade of his life that the Soviet Union existed.  Most of his time doing horticulture and breeding he was poor and his work unrecognized.  It was under these relatively meagre conditions that he gained his experience, developing his principles, methods, and new cultivars.

One of the things that makes intuitive sense as Michurin fleshes it out is the concept of plasticity.  He uses this term repeatedly throughout his writings, and talks about a spectrum from plasticity to stability.  The most stable varieties have the greatest potency of hereditary force, while the most plastic young seedlings can be imprinted and trained in novel ways (such as the ability to root from cuttings or adapt to a different climate). On the highly stable end of the spectrum would be a wild perennial plant that has been growing vegetatively for a long time, and of course with a relatively larger amount of biomass compared to a young seedling.  On the other extreme would be a young seedling, even more so a hybrid seedling.  And even more plasticity when it’s a distant hybrid.  Crossing plants from different climates will yield more plastic seedlings than crossing localized ones. All of these constitute various types of stresses for an organism.  Michurin realized that you can layer additional stresses on by grafting and pruning these plastic young hybrid seedlings. Likewise, an increasing distance in the rootstock/scion relationship is another form of stress.  It was the technique of mentor grafting based on these observations that allowed Michurin to answer the question of the conditions under which graft induced variation occurs.

Michurin worked with a wide variety of plants in his life, and one time even worked on tea in the relatively warm climate of Sochi.  But later he made it his focus to expand the range of cultivated fruit trees into the colder parts of the country.  Michurin developed many novel methods to aid hybridization including mentor pollination, preliminary vegetative approximation, use of a bridge species, mentor grafting, and intraspecific crossing prior to interspecific and intergeneric crossing.  Less well known is that he worked as an electrician and experimented with the impacts of electromagnetism on plants, and found in particular that “the exposure of pollen and female generative organs to static electricity and other biophysical factors increased the efficiency of distant crosses” (source). What’s interesting is that now approaching an 100 years since Michurin passed, despite his ideas having largely been confirmed in the scientific literature, his work is not widely known by plant breeders today outside of certain areas.  Compare this to Mendel, who everyone learns about in the first semester of biology. It’s interesting to compare Mendel with Michurin, as they have totally different emphases: annuals vs. perennials, inbred vs hybrid, qualitative vs. quantitative traits, transmissional vs. developmental genetics (see more).

One of the most common cultivars of Michurin’s in the US is his xSorboaronia mitschurunii which has been renamed and is grown at scale for “Aronia” berry production. His arguta kiwi “Ananasnaya Michurina” (usually called Anna) is still considered one of the best cultivars of the species and is also widely grown. In Europe there are many more of his cultivars available. For more information on his cultivars and ideas about breeding and selection see this paper from 2015 in the Latvian Academy of Sciences. Beyond the cultivars that Michurin himself released, he inspired many researchers to attempt distant hybridization with novel methods. For example, the first Diospyros kaki x virginiana (asian persimmon x American persimmon) was obtained in Ukraine and said to have been made possible by grafting prior to crossing. Many new cold tolerant, large fruited persimmon cultivars were descended from this original cross (though later new F1s were made via embryo rescue). Much of the work inspired by Michurin’s principles and methods is not well known and is part of what I will explore in future posts.

Photo of a Physalis longifolia scion growing on a horizontally bent Physalis peruviana.

The environment is of course a familiar concept for us, particularly in the West. The surroundings, the outside. But for most people its a leap for them to consider the blood in their vessels as a river. The concept of the environment therefore tends to act as a hinderance, a separation of relation. In the West, we have a tendency of reification—making things or boundaries more real or solid than they actually are. If its challenging to see the environment as you, maybe its easier to see yourself as the environment. The practical aspect of a definition shows up in how it can either open or close experimental (and experiential) pathways to us.

Part of the idea of this substack is to explore certain concepts in ways that might lead to different approaches to plant breeding and crop development. Posts will relate to garden experimentation, scientific studies, and plant breeding principles and methods. It’s hopeful to imagine a world where mosaics of home gardeners and smaller scale growers can, without sophisticated technology, serve as factories of biodiversity for new crop development. In a way it’s a big idea, but really it’s a small seed, ready to sprout when the right conditions meet our inherent human capacities.

Some seedlings from this year — Helianthus tuberous ‘Rode’ x ‘Dwarf’ and Lycium ‘Stardust’ x ‘Large Leaf’

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