THE AMERICAN CHESTNUT PROJECT
Progress Report 2022

Moving past 10,000 Trees

Activities undertaken between December 2021 and November 30, 2022

We had another exciting year with significant progress toward our goals of distributing the blight tolerant, Darling American chestnut trees to the public and restoration programs.

First, I would like to introduce Dr. Andy Newhouse and congratulate him on his promotion to Co-Director of the chestnut project this year. Andy has 15 years of experience on the project doing research, managing the field permits, as the lead author on all the regulatory submissions, and transitioning into a leadership role. Having a mid-career leader will ensure the project will continue far into the future.

Regulatory progress, long awaited news

2023 will be an exciting year because we are predicting we will finally have federal regulatory approvals and can begin distributing the blight tolerant, Darling American chestnut trees. The USDA APHIS BRS, the lead agency in the regulatory coordinated framework, has predicted a decision by Aug. 2023. But it might come much sooner, and distribution could begin before the growing season starts in May and pollination season in June/July. Drafts of the USDA's Plant Pest Risk Assessment (PPRA) and the Environmental Impact Statement (EIS) are posted for one final 45-day public open comment period. We hope that everyone reading this update will participate by sending in positive comments that you want these trees for your own use as well as for restoring the  forest ecosystems. Deadline for comments is Dec. 27th, but please send in as soon as possible. We have created a special web page with a summary of keys points of the lengthy USDA documents.

The EPA is expected to make their decision on the registration and tolerance exemption for the Darling American chestnut by Dec. 31, 2022. The FDA's consultation response will likely soon follow the EPA’s decision. Since this process is coordinated between the three agencies, they may try to make their decisions as close together as possible. Therefore, we are predicting a release date this spring, but as always, this is not in our hands, and the regulators have the final say.

Tree Production

The original goal of the Ten Thousand Chestnut Challenge is in its name: to produce 10,000 transgenic American chestnut trees. This year our overall harvest surpassed that number! Some of these are non-Darling events, and others will be needed for continuing research, such as long-term environmental tests and stacking blight and Phytophthora resistance genes by crossing with backcross trees. We are also preparing for general releases by planting holding plots and planning for seed-production nurseries.

Therefore, our current challenge is to see if we can produce 10,000 fully American chestnut Darling seedlings in a single year. This year will be our closest so far towards that goal. ESF harvested a record number of hand-pollinated nuts using 17 transgenic pollen sources (dads) and 175 mother trees. This produced 11,700 American chestnut seeds, over twice as many as the 5,378 harvested last year. Most of these are T3 crosses (third generation), but this number also includes 560 T4 (fourth generation) and 670 T5 (fifth generation) offspring nuts. There are also 600 nuts from our newest 'DarWin' line, which combines the OxO gene from Darling (Dar) with a wound and pathogen inducible promoter (Win) (see Carlson et al. 2022 in publication list.

ESF students and staff harvesting the 2022 chestnuts

As described in the past, we are crossing with wildtype mother trees to enhance genetic diversity, so only half of the offspring inherit the OxO gene that confers the blight tolerance. Actual inheritance rates usually fall between 40-50% due to challenges of hand pollination. The nuts won’t be tested until this winter, but our conservative estimate would be approximately 5,000 transgenic nuts, which puts us halfway to our yearly goal. We have also shared our transgenic pollen with collaborators at TACF and the University of New England. Depending on their harvest numbers, we may reach our goal this year. But if they don’t, we will almost certainly do so next year when we have regulatory approvals and can expand our pollen distribution beyond our current USDA permitted sites. We are making excellent progress.

Ramping up Tree Production

So, what’s next? Producing 10,000 seedlings per year is a great accomplishment and will enable initial distributions of trees to the public. But for meaningful forest ecosystem restoration, we need to go big. The question is, can we ramp up to a million trees per year within the next decade? Many more low-priced trees are needed for large-scale, landscape restoration projects. We have plans to work with TACF and citizen scientists to help us with the initial ramping up of production once we have regulatory approval. With their help, we should be able to ramp up well past 10,000, possibly even going over 100 thousand trees per year during the next few years. But to get to a million, we need to dedicate large orchards and a high thruput testing facility for tree production. The testing facility would be of use immediately for the nuts produced by hand pollinations. The scaled-up orchards will take ten years to fully establish, so we need to begin them now for efficient future production. In the interim, we will work closely with our partners using the pollen distribution and hand pollinations to maximize tree production.

Publications this year

• Onwumelu, Anuli, William A. Powell, Andrew E. Newhouse, Garrett Evans, Gwen Hilles, Dakota F. Matthews, Vernon Coffey, and John E. Drake. “Oxalate Oxidase Transgene Expression in American Chestnut Leaves Has Little Effect on Photosynthetic or Respiratory Physiology.” New Forests, April 19, 2022. open access web publication
• Carlson, Erik, Kristen Stewart, Kathleen Baier, Linda McGuigan, Tobi Culpepper II, and William Powell. 2022. Pathogen-induced expression of a blight tolerance transgene in American chestnut. Molecular Plant Pathology. 23:370-382 open access web publication