Progress report for FNC23-1359
Project Information
• WESTON ADAMS (project coordinator) has been working with persimmons for nine years in Linden, TN. During the final class of his undergraduate program in Sustainable Food and Farming (Umass Amherst), he wrote a paper on persimmon genetics and breeding, and since that time he has continued to study this topic of interest. Weston has been involved in small-scale nursery production of hybrid persimmons since the spring of 2022.
• CLIFF ENGLAND from England’s Orchard and Nursery (nuttrees.net) has bred persimmons for many years, and he has agreed to assist Weston. Many of the novel new hybrid persimmons on the market were released from Cliff’s farm where he tends one of the largest persimmon collections in North America. Weston intends to utilize both Cliff’s expertise and his specimen trees in the breeding activities explained below.
• MATT RENKOSKI was awarded a SARE grant for persimmon research in 2020, where he studied methods of grafting cultivated persimmon onto stands of wild trees. He currently grows approximately 400 persimmon trees on his farm in central Missouri. Matt has offered his rare hybrid persimmon specimens for use in the breeding work described below.
***2024 UPDATE***
• In addition to the collaborators listed above, ANTHONY CZAJA has agreed to help on this project. Anthony has been involved with small-scale fruit production for multiple years on his homestead in Southern Alabama. He has grown persimmons and he has been so impressed with their adaptability and disease resistance that he intends to go "all out" on persimmons (he intends to plant many more). He is also interested in persimmon research and he has agreed to make his land available for planting research trees that CANNOT currently survive in the NC-SARE region, but which are critical to the development of new hybrids which CAN survive in the NC-SARE region.
Growers throughout North America and in the southern NC-SARE region have realized that persimmons are one of the simplest fruit crops to grow without pesticides and heavy fertilization. Persimmons resist many diseases and increase consumer access to local, nutritious food. As more and more people grow this fruit, the public is acquiring a taste for all types of persimmons. But for many people, non-astringent persimmons (such as ‘Fuyu’) are still considered the most desirable. Unlike astringent cultivars, non-astringent varieties can be shipped and eaten while they are still firm.
Breeders have labored to develop persimmon varieties that produce desirable fruit and also tolerate the winter conditions found throughout the southern NC-SARE region, however their work is far from finished. Cold-hardy hybrids between wild persimmon (Diospyros virginiana) and the oriental persimmon (Diospyros kaki) have been released and eagerly received by growers, but so far there have been no non-astringent hybrid persimmons released to growers in the NC-SARE region. This means that growers cannot easily compete with consumer expectations set by California and other warm regions. As of now, non-astringent persimmons primarily grow in zone 7 and southward, which excludes all of the NC-SARE region. But this could potentially be changed.
****2024 UPDATE***
The goals of this breeding project continue to be incredibly relevant. This past January (2024) we have experienced extended cold snaps throughout Missouri and surrounding portions of the NC-SARE region. The temperatures were low enough to readily kill most of the non-astringent cultivars of persimmon currently available. These weather events underscore the need for a cold-hardy hybrid that also produced non-astringent fruit.
Persimmon breeders must focus their efforts on developing a non-astringent hybrid persimmon variety that can withstand temperatures commonly found in the southern portions of the NC-SARE region. Doing so would make an easy-to-grow and nutritious food item available to growers throughout the southern NC-SARE region and in other parts of North America. I have been working with a few others on a plan to tackle this problem.
I will describe below the genetics behind my proposal, but in short, we have determined that backcrossing the 50/50 Diospyros kaki/Diospyros virginiana hybrid persimmon known as Mikkusu (aka JT-02) to a non-astringent cultivar such as Hana Fuyu could potentially generate a new cold-hardy, non-astringent hybrid cultivar of persimmon suited to parts of the NC-SARE region where non-astringent persimmons are currently very difficult to grow. Replicating this cross up to 1000 times will greatly enhance our chances of generating the desired variety or varieties.
Persimmons have complicated genetics, but the strategy proposed here has been affirmed by numerous enthusiasts. Typically, the non-astringent trait in persimmon is inherited recessively. Couple this with the hexaploid nature of persimmons, and it's understandable why generating F1 non-astringent cultivars is difficult. For this reason, researchers have resorted to carefully-planned backcrosses in traditional breeding programs. And in the case of hybrid persimmons, the backcross we propose is similar. It fits the following form:
(American persimmon x non-astringent Asian persimmon) X non-astringent Asian persimmon
To launch the project, I am working with a few sources to secure the pollen I need for this breeding work. I'm in touch with Jenny Smith at the National Clonal Germplasm Repository. She has agreed to send any pollen she can collect from the UC Davis repository. Since pollen can be scarce, I am also making connections with private parties who may be able to supply pollen if needed. Pending successful acquisition of pollen, I intend to hand-pollinate flowers from Mikkusu (aka JT-02) hybrid persimmon trees at both Matt Renkoski's persimmon farm and also Cliff England's persimmon farm. Pollinated fruits will develop over the summer of 2023, and in the fall, hybrid seed will be harvested and prepared for stratification. The breeding cycle will be repeated in 2024 to generate a second round of seed.
Although I live in the NC-SARE region, and our project is based in the NC-SARE region, I am asking permission to cooperate with two individuals: Matt Renkoski from Missouri and Cliff England from Kentucky. I will explain. The breeding goals of this project is very specific, and to meet the goals, I MUST have access to a specific hybrid genotype for breeding purposes: namely the Mikkusu (aka JT-02) hybrid already mentioned. This is the ONLY cultivar I am aware of which will meet the genetic constraints required for the project. The Mikkusu hybrid has indeed been planted within the NC-SARE region, but only in very small quantities. I have not been able to locate enough JT-02 trees within the NC-SARE region to complete the project. This is why I also intend to cooperate with Cliff England of Kentucky.
I will reiterate the project objectives.
- Generate anywhere from 200-1000 persimmons seeds from a cross of Mikkusu x non-astringent with the goal of developing a non-astringent, cold-hardy hybrid persimmon variety.
- Increase awareness of persimmons as a fruit crop well suited to the southern NC-SARE region and beyond through social media and a progress report published in Pomona (the journal of North American Fruit Explorers).
- Empower prospective persimmon breeders by hosting a persimmon-breeders' virtual workshop through North American Fruit Explorers. The workshop will be recorded and made available as a digital resource.
****2024 UPDATE****
We are still pursuing the genetic strategy outlined above, but we have run into some challenges which I will briefly outline here, and I am proposing a new approach to the same project.
Though we conducted an estimated 190 controlled pollinations across 3 separate farms in the spring of 2023, our team was disappointed to find that our pollinated blossoms yielded very little seed. On December 3, 2023 seven persimmon enthusiasts--including those who are working with me on this project--joined a zoom call to discuss why we were not getting the seed we wanted. For a full update on the 2023 breeding developments, please reference the educational article which has been attached to this report and also submitted to journal of the North American Fruit Explorers (NAFEX) for publication; but in short, we have concluded that we have likely have inadvertently been working with dead pollen in 2023. Most likely the pollen we received in the mail had lost much of its viability by the time it reached us. We believe that this is why we have not obtained the seed we desired.
According to our original grant proposal, we were planning to repeat in 2024 the pollinations that we made in 2023. However, based on what we learned in 2023, I believe that we should adjust our approach slightly. In order to address the problem we have encountered, I am proposing a shift in strategy and a slight broadening of our goals.
I am proposing that we halt the complicated pollination trips for 2024 and instead focus our remaining funds on three specific things. I will describe each of the three items below.
1) First, I propose that we establish a small research orchard in southern Alabama which will be designed specifically for the production of the hybrid seed described in our proposal. It would be ideal if this orchard could be located in the NC-SARE region, but since we are working with cold-sensitive trees our Missouri climate would certainly kill critical trees in the research planting. For this reason, we must plant a satellite orchard down south in order to breed trees that can be grown up north. This model has been used before by persimmon breeders such as Cliff England and Jerry Lehman, and it has proven to be a viable breeding strategy. Large number of seed can often be generated through natural insect pollination rather than through expensive and labor-intensive hand pollination. Further, I have located an individual in southern Alabama by the name of Anthony Czaja who is willing to work with us in establishing a small research planting on his land. By investing funds in a small research planting, we will be able to potentially generate many more hybrid seeds than we would be by tediously performing each cross by hand.
2) Second, I propose that we invest portion of our remaining funds into testing genetic markers that could be used to conduct marker-assisted selection of hybrid persimmon seedlings. Genetic markers are used by plant breeders to identify at the molecular level plants that have specific and desirable phenotypic traits. Breeders can work with labs to screen young seedlings for these markers and discard the seedlings that clearly do not meet breeding objectives. Genetic markers could greatly speed up the breeding and development process with this crop.
Breeders know that when seedling hybrid persimmon trees seedlings are grown out in an orchard, a very high percentage of the trees will end up being males. These trees take up space in the orchard and consume resources, but they never produce fruit. Further, since this project is focused on developing a non-astringent hybrid, we not only want female trees; we also want female trees that carry the non-astringent trait. A review of the literature reveals that genetic markers have been developed for both of these traits.
Blasco et al. (2020) published on some genetic markers that have been proven to reliably identify astringent phenotypes of Asian persimmon (Diospyros kaki) and also to identify specimens that will produce at least some male flowers. The authors did not study whether these markers could be used in Diospyros virginiana or in persimmon hybrids, but if they can be shown to function well in hybrid genomes, the benefit to hybrid persimmon breeding would be very significant. I am proposing that we invest a portion of our remaining grant funding to test whether the genetic markers used in Diospyros kaki can also be used in Diosypros virginiana and Diospyros hybrids. This will likely involve collaboration with one or more DNA facilities/labs who will receive samples of known phenotypes and screen those samples based on the markers we provide from the literature.
If the genetic markers which have been used in Diospyros kaki could be applied in hybrid persimmons, the breeding process would be greatly accelerated.
3) Third, I am proposing that we invest a small amount of our remaining funds in continuing a branch of our work which we have already begun--the chemical treatment of female persimmons trees with silver thiosulfate--to see if male blooms can be induced. Silver thiosulfate has been used in other crops to induce male blooms on genetically female trees, but there is very little if any literature which discusses the induction of male blooms on cultivars of persimmon. If we discover that silver thiosulfate could induce the production of male blooms on persimmon as it does on some other crops, the implications for persimmon breeding would be significant.
Blasco, M., Gil-Munoz, F., del Mar Naval, M., Badenes, M. L. (2020). Molecular Assisted Selection for Pollination-Constant and Non-Astringent Type without Male Flowers in Spanish Germplasm for Persimmon Breeding. Agronomy 2020, 10, 1172; doi:10.3390/agronomy10081172
Research
Work on this project commenced in earnest this past spring! I spent hours communicating with growers nationwide to secure pollen from PCNA-type cultivars for use in breeding. We knew that this task would be complicated by the fact that most PCNA cultivars do not produce male flowers. Those that do produce male flowers only do so sporadically. Although I communicated with an estimated 35 growers about this need, the USDA repository at Davis was the only reliable pollen source I found. From the USDA, I was secured pollen from the PCNA cultivars Hanagosho, Okugosho, and F-444. Even though the pollen was supposed to be overnighted, it took a couple days to reach us. As soon as I did receive it, I promptly transferred the pollen to frozen storage.
In May 2023, I took some days off work and traveled to the farms of Matt Renkoski, Darren Bender-Beauregard, and Cliff England. Each of these gentlemen were cultivating mature specimens of the JT-02 hybrid, and each was willing to utilize their specimens as pollen parents in the current breeding research. In addition to petri dishes and other needed supplies, I carried a portable DC-powered freezer to keep pollen in cold storage during travel.
Soon it was time to start work in the field! In order to prevent contamination from foreign pollen, I was required to bag unopened flowers with empty tea bags prior to pollination so that insects would not have access to them. Since persimmon blooms open before dawn, I frequently bagged my candidate blossoms in the evening in preparation for the next day. One or two mornings also found me up early in the dark hours of the morning bagging blooms before pollinators had become active.
The pollen we received from the USDA came in test tubes the form of dried anthers, and before use, the pollen grains had to be separated from the anthers. After some experimentation in the field, I discovered that an organza jewelers’ bag and petri dish helped to make very efficient use of the small quantity of pollen we had. I dumped the dry anthers into the jewelers’ bag and shook the bag carefully over a clean petri dish. Pollen grains would fall into the dish and create a thin, yellow layer on the clear plastic. At this point the pollen was ready to apply to the receptive blossoms.
I carefully inspected each bloom that had been bagged the night before to determine which ones had opened and become receptive to pollen. These flowers were then unbagged, stripped of petals, and dipped carefully into the petri dish of pollen. The pollen quickly adhered to the tacky surface of the stigma. Blooms were then promptly re-bagged. By dipping the stigmas directly into the petri dish (and skipping the paint brush method of pollen application), I was able to get many, many crosses from a small quantity of pollen. Each cross was tagged with flagging tape and labeled to document the donor pollen parent. In total, we conducted upwards of 180 controlled crosses amongst the 3 participating farms this past spring.
From the 180 crosses we conducted this spring, a fair number of fruits developed. We had some fruit abort over the summer—as is typical—and by harvesttime we had 40 hand-pollinated fruits to harvest. But as we opened these fruits and began extracting the seeds, we discovered something that sent us back to the drawing board for a little bit—most of the fruits were completely devoid of seeds! Of 40 fruits, we obtained 12 seeds. What was going on!?
This was a disappointment, needless to say, but it prompted us to reevaluate our breeding structure. Where was the missing link? Specifically, we looked at three primary factors that could have affected our results. 1) Hybrid sterility, 2) technician error, and 3) pollen inviability. On December 3, we held a zoom meeting with more than half a dozen U.S.-based Diospyros breeders or enthusiasts to discuss the challenge and identify the point of breakdown. In this meeting a participant shared that his JT-02 is reliably generating seeds in California via open pollination with D. kaki. This confirmed that we are likely not dealing with any sterility/incompatibility problem. Technician error is another possible factor. I personally conducted most of the controlled crosses, and while I have not conducted Diospyros crosses before, I have communicated with persimmon breeders in preparation for this project and I have also conducted many successful hand pollinations in other crops (Zinnia, Viola, Citrullus, Solanum, Cucumis, and Cucurbita). I believe our timing and application protocol was in line with standard industry principles. That leaves us with the third issue: inviable pollen.
The USDA was incredibly helpful in providing pollen this spring, but I have my doubts about the viability of the pollen we received. The pollen was shipped overnight to us, but the package was delayed by a day in shipment. Further, the USDA collected pollen on multiple days, so pollen was stored in refrigeration during the intervening holding period. On the inside of one vial of pollen that we received, I also spotted a small amount of condensation. These factors collectively cause me to question the viability of the pollen we received. I currently believe that pollen viability was responsible for the issues we dealt with—at least this past year.
😎 Looking Ahead 😎
The genetic basis of our project is solid, but the logistics of creating the cross have been challenging. With this in mind, I am pursuing three directions for this project in 2024, as described in the updated project objectives. 1) I would like plant a small orchard in southern Alabama which will be designed for research/breeding work. The rational behind this is described in Project Objectives. 2) I would like to invest some resources in testing genetic markers--which are typically used on Diospyros kaki--to see if they function the same in Diosypros virginiana and in hybrids. And 3) I would like to continue the research we have already started to see if male blooms can be chemically induced on female persimmon trees using silver thiosulfate.
😋 Farewell 😋
My observation is that more and more people are seeking to grow persimmons throughout North America, and it’s exciting to be working with the crop. The press is talking about persimmons, and lively discussion about this wonderful fruit continues across online platforms and elsewhere. I am thankful for the support of people at NAFEX and abroad as we pursue this worthwhile project. Persimmons are a miracle of Creation, and we are blessed to be involved with the future of this fruit.
Educational & Outreach Activities
Participation Summary:
In 2023, outreach occurred via a few different methods. I will highlight the primary ones here.
- Facebook updates posted to the "Persimmon World" Facebook group helped to keep a handful of other enthusiasts aware of project developments this spring as we conducted pollinations. The posts helped to increased publicity for our project and generated some discussion surrounding our activities.
- In the fall of the year, I wrote a project update to be published in the fall 2023 issue of Pomona, the journal of North American Fruit Explorers. The editor chose to hold the article for publication in the winter (when it's harder to get written articles due to the holidays), and this past month I sent her an updated version of my article. The article has yet to be published, but upon release it should give many North-American rare fruit growers a peak into the work we have been doing!
- Our project received some bonus publicity this fall when Hannah Walhout from FoodPrint contacted me to conduct a brief email interview! She intended to run a feature on persimmons, and she wanted to hear a few words from the ranks of persimmon breeders! Here feature on persimmons, which includes a reference to the project we are undertaking, can be viewed here: https://foodprint.org/blog/eat-seasonally-this-winter-with-persimmons/
- Out of necessity we called a meeting on December 3, 2023 to discuss the challenges we were having obtaining hybrid seed! The collaboration helped me formulate a theory as to what was going wrong, and it allowed us to discuss project goals with a few other persimmon enthusiasts.
Learning Outcomes
We've already learned some interesting things....but my hope is that this year we can gather some more pertinent info that will be helpful to the persimmon breeding community.