Progress report for FNC23-1359
Project Information
All of the cooperators on this farm have had an interest in low-maintenance fruit crops and have grown these crops at our respective farms for many years. We have used traditional orchard layout, forest farming, and silvopasture practices; and for many of us, persimmons have been a crop of increasing interest due to their low input requirements, their impressive disease-resistance, and their reliable cropping where many other fruits fail. Weston and Darren have grown persimmons on a homestead scale and sold the grafted trees for some time now. The historical roots of Cliff England’s operation go back as far as 1960, and Matt Renkoski was a recipient of a SARE grant around 2020 as he launched his persimmon orchard grafted on wild seedlings of Diospyros virginiana. Jamie currently manages a grove of Satsuma oranges in southern Alabama. We’ve all been interested in shifting our farms toward sustainability, and for many of us persimmons have been part of the transition.
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.
We are working to lay the foundation for breeding a non-astringent hybrid persimmon. Using two genetic approaches (described under Project Objectives) we are seeking to put into practice some breeding ideas that until recent time have primarily existed in theory among persimmon enthusiasts. As we do this, we are seeking to reach out and educate the fruit-growing community about the potential of this crop and how they can use it in their operations.
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 two possible paths to obtaining a non-astringent hybrid persimmon. First, we could attempt to harness the Japanese PCNA non-astringency allele found in Fuyu and many other Japanese non-astringent persimmons. Second, we could bring in the dominant non-astringency allele originating from China and observe the phenotype that this produces in the hybrid.
The first method involves 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. Mikkusu is a cross between a Japanese non-astringent persimmon and a wild American persimmon. The Japanese non-astringent trait that we are discussing is inherited recessively, so we can assume the non-astringent parent of Mikkusu carried 6 copies of the allele in its hexaploidy genome. Traditionally, researchers have resorted to carefully-planned backcrosses in to generate new non-astringent Japanese persimmons, and in the case of hybrid persimmons, this first backcross we are working on is similar. It fits the following backcross form:
(American persimmon x non-astringent Japanese persimmon) X non-astringent Japanese persimmon
The consensus among many well-studied persimmon enthusiasts is that this genetic combination 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 as many times as possible will greatly enhance our chances of generating the desired variety or varieties.
But there’s another genetic combination that enthusiasts have been discussing. This is the cross that utilizes the dominant non-astringent trait discovered in China relatively recently. The phenotype (non-astringency of underripe fruit) is similar, but in this case its controlled by a dominant gene. It’s a cross that we have chosen to incorporate into this breeding project only recently, largely because we’ve been able to secure germplasm of the rare Chinese non-astringent persimmon type.
Being a dominant allele, the form of this cross is much simpler. Most likely, we will utilize a hybrid male (75% Diospyros virginiana and 25% Diospyros kaki) crossed to the Chinese non-astringent female that we have been able to obtain. The hope in this cross is that the dominant non-astringent gene from the Chinese line will have a similar effect on the hybrid phenotype as it does on the Chinese D. kaki phenotype.
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 and in consultation with SARE we have adjusted our approach slightly and we have proposed a shift in strategy and a slight broadening of our goals.
Instead of the complicated (and costly) hand pollination trips which even at their best can only yield a limited number of seeds, we have been focusing on a new approach.
1) First, we are establishing a small research orchard in southern Alabama that is 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 Jamie Whitaker who is willing to work with us in establishing a small research planting on the farm she manages. 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 tree 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. Some of our funds are going to pave the way for testing these markers in Diosypros virginiana and Diospyros hybrids. We plan to optimize the markers with CPS Labs in Pleasant Grove, CA so that samples of material can be sent to them in the future to screen for these markers.
If the genetic markers which have been used in Diospyros kaki could be applied in hybrid persimmons, the breeding process would be greatly accelerated.
It should also be noted that we have completed a test treatment of a female Asian non-astringent persimmon (Diospyros virginiana) with Silver thiosulfate, the ethylene-blocking compound that has been used in some crops to generate male blossoms on female plants. We treated the tree in early summer (at the time when we expected next years primordial fruit buds to be forming) and also in the spring using a rate that has been proven to work on cucumbers. More research would be needed for conclusive results, but our preliminary tests indicate that silver thiosulfate may not have the same effect on female persimmon trees as it has on female plants of other species. We did not obtain any male blooms on our tree.
This project continues to be an excellent learning experience, and we look forward to conducting some additional educational activities in the final year. We intend to hold a hybrid persimmon interest meeting through the North American Fruit Explorers next season, which will help to generate further exposure to the crop we are working and will also help us publish our work.
We've had to acknowledge that this project in its entirety goes beyond the scope of a 2 or 3-year grant, but this phase of the project is allowing us to lay the groundwork for likely future breeding successes.
Just to reiterate, we hope to accomplish the following goals in the final phase of this project.
- Complete the establishment of a small research persimmon planting in southern Alabama. This planting will be designed specifically to accomplish the breeding objectives outlined here.
- Optimize some molecular markers for non-astringency and the male-flowering trait in Diospyros kaki, and run preliminary tests to see if these markers can be utilized in hybrid genotypes.
- Empower prospective persimmon breeders by hosting a virtual hybrid persimmon interest meeting through North American Fruit Explorers. The workshop will be recorded and made available as a digital resource.
Cooperators
- - Technical Advisor (Educator and Researcher)
- (Researcher)
- (Researcher)
Research
Our project began in earnest spring of 2023. And although we learned some good things, the activities of the spring caused us to shift our strategy slightly.
I spent hours searching for sources for pollen, and in the end, we ended up utilizing pollen from the USDA persimmon repository in Davis, CA. I purchased a small portable freezer and drove through multiple states to conduct hand pollinations at different farms in Missouri, Kentucky, and Indiana.
The spring pollinations were done with great care. In order to prevent contamination from foreign pollen, I was careful 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 was carefully separated from the dried anthers using an organza jewelers’ bag and petri dish helped to make very efficient use of the small quantity of pollen we had. 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. But alas, we were to be (mildly) disappointed. When we returned to these pollinated fruits in the fall, we discovered that most of them were devoid of seeds!
Based on my research in hand pollination work at Baker Creek Heirloom Seeds (where I am employed) and also based on the information I have gathered from Cliff England and others, I believe our pollination technique was correct. Also, I have spoken with Ram Viswanathan who had obtained many seeds from Mikkussu x Diospyros kaki by open polliation, so I have reasonable confidence that the cross we are attempting is a compatible cross. This leaves the likelihood that the pollen we received from California was no longer viable by the time we performed the pollinations. And it also caused us to rethink the effectiveness of our methods!
Instead of hunting country-wide for pollen and then traveling across states to make a limited number of hand pollinations, we’ve decided to invest in a small research planting in southern Alabama. This orchard will be designed so that through open pollination we can hopefully obtain hundreds (or thousands) of the seeds that we were laboring so hard to get through hand-pollination. It’s a slower, long-term breeding plan, but with more potential. The genetics of the cross we are attempting have not changed, except that we have added a cross with the Chinese dominant PCNA gene as a second prong to our breeding approach. This is possible because we recently obtained germplasm of the Chinese PCNA persimmon genotype.
Also, have put some resources into completing our Silver thiosulfate experiments and we are in the process of optimizing molecular markers for persimmon. These markers will be specifically for the Japanese PCNA trait, as well as for the male-flowering trait in Diospyros kaki. It is yet to be determined whether these markers will be useful in hybrid genomes.
In spite of setbacks, this project has already turned out some useful information and it is facilitating networking of persimmon enthusiasts. The difficulty we experience in getting seed set prompted us to dig into the compatibility of the crosses we are conducting. Ram Viswanathan was able to confirm for us that the Mikkussu F1 hybrid is indeed cross compatible with Diospyros kaki. Previous work has already shown that F1 hybrids between D. virginiana and D. kaki are backcross-compatible with their American parent, so it’s helpful to confirm that these hybrids—and this genotype in particular—can also be compatible with their oriental parent.
The genetic basis of our project is solid, but the logistics of creating the cross have been challenging. This is why we’ve adjusted our approach. 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 privileged to be involved with the future of this fruit.
Educational & Outreach Activities
Participation Summary:
Outreach has occurred via a few different methods. Many of these outreach activities occurred in 2023, and moving into our last (extension) year of the project we plan to do additional outreach.
- Facebook updates posted to the "Persimmon World" Facebook group helped to keep a handful of other enthusiasts aware of project developments as we conducted pollinations. The posts helped to increased publicity for our project and generated some discussion surrounding our activities.
- In the fall of 2023, I wrote a project update which was published in the winter 2024 issue of Pomona, the journal of North American Fruit Explorers. It gave many North-American rare fruit growers a peak into the work we have been doing!
- Our project received some bonus publicity fall 2023 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
In the course of this project so far, we've been able to confirm that F1 persimmon interspecific hybrids between Diospyros kaki and Diospyros virginiana have the potential to backcross successfully to both of their parents. I (the project coordinator) knew that they had the potential to backcross to their American parent, but it was not until my conversation with Ram Viswanathan that I confirmed backcross compatibility to their Oriental parent.