Show Notes & Links

Connecticut Agricultural Experiment Station

Lockwood Farm, Hamden

The American Chestnut Foundation

Students Take Root in Chestnut Tree Restoration Effort, Southern Connecticut State University

“Genomic approaches to accelerate American chestnut restoration” by Westbrook, J. W., Malukiewicz, J., Zhang, Q., et al (2026), published in Science, 391(6786), 730–735.

Episode Transcript

Rachel Jeffrey
But the reality is, this is a long project. This is a long — in my lifetime, in my children’s lifetime — will they see a difference? Perhaps, but maybe not. And so, I think that’s something so different that we need to think about with these ecology and forestry questions. How can we do it in a way that is careful and sustainable, but it’s not fast…

Tan Deleon
On behalf of the Academy’s members, welcome to Learning and Living STEMM in Connecticut, the podcast of the Connecticut Academy of Science and Engineering. My name is Tanimu Deleon. I’m an elected member of the Academy and serve as an officer on its council. I invite you to learn more about the Academy by visiting our website at ctcase.org. Today we will talk about Connecticut-based research related to the restoration of American chestnut. One project is coordinated by our local chapter of the American Chestnut Foundation. The goal is to create an American chestnut resistant to a destructive fungus that causes a disease called chestnut blight. Potentially only 1,000 American chestnuts are left in Connecticut, and they are isolated and struggling. The second project we’ll cover is coordinated by the Connecticut Agricultural Experiment Station (CASE). This project relates to the biological control of chestnut blight using hypoviruses. The goal of this work is to build a capacity for biological management of chestnut blight to support the survival of existing American chestnut trees. I am joined today by two guests. First is Dr. Rachel Jeffrey, Chair and Associate Professor of Biology at Southern Connecticut State University, and Co-Director of Behavioral Neuroscience at Southern. Our second guest is Dr. Susanna Keriö. She is an Assistant Agricultural Scientist II in the Department of Environmental Science and Forestry at the Connecticut Agricultural Experiment Station. Welcome, Rachel and Susanna, and thank you for joining me on this podcast today. Before we start, would you both please share a bit about your backgrounds? Rachel, would you start?

Rachel Jeffrey
Sure. Thank you so much for having me today. I am a biology professor, but certainly not a botanist by training. But I grew up in Vermont. I spent a lot of time hiking, being out in the woods. Really enjoy watching our New England forests change, especially after doing some graduate work in California and scrub desert. But I’ve been trained my whole life working inside labs, and I’ve been really blessed to be a part of the larger project here with the American Chestnut Conservation to be able to take some of my academic ideas and act more like a citizen that just cares about our ecology and our environment, and hopefully to connect some of my students with those ecology problems.

Tan Deleon
Thank you. Susanna?

Susanna Keriö
Thank you for having me here today. My background is actually in forest pathology and forest ecology, so I could tell that, or I could say that I am really a tree enthusiast. Anything related to trees excites me so much. I did my PhD research at the University of Helsinki in Finland, and then I did my postdoctoral research at Oregon State University. My research is currently very much centered on how we can improve the resilience of trees to various abiotic and biotic factors, including pathogens that affect tree health, and my current research at the Connecticut Agricultural Experiment Station focuses on how trees respond to stress at the physiological, chemical, or molecular level, and how these various stress response patterns can be used to diagnose tree health issues and to manage tree health. More recently, and related to the topic of chestnuts, about a year ago, I initiated a research project that leverages mycoviruses. In the management of chestnut blight.

Tan Deleon
Oh wow! Okay, so, with respect to CAES, is there, do they do other things in and around Connecticut?

Susanna Keriö
Yes. So, actually, the Connecticut Agricultural Experiment Station, or CAES for short, is a state-operated research institution. We have approximately 92 full-time scientists, research technicians, administrative personnel, and support staff at the institution. Additionally, each year we hire close to 50 research assistants, which offers employment opportunities for students who are aspiring scientists. Besides that, so very much the mission of the Connecticut Agricultural Experiment Station is to produce and disseminate scientific knowledge in order to improve agricultural productivity and environmental quality to protect plants and enhance human health and well-being. So, we achieve this mission by conducting research that benefits the Connecticut residents and the nation as a whole.

Tan Deleon
So, thank you, Susanna. That was a really good synopsis of CAES. So, let’s get into the chestnut, the American chestnut. What has happened to the chestnut, and why is it so important, not only to the country but also to Connecticut? And Rachel, we could start with you.

Rachel Jeffrey
All right, my answer will be much less floral than Susanna’s with her research. When I came back to Connecticut, I bought my first house, and it was a 1920s Craftsman in Hamden, and it was built out of American chestnut. And my home inspector came in and said, “Oh my gosh, this is so cool! All of this floor, all of these, the trim that you see on the walls, this is all American chestnut,” and it was so good for building. It was so important to Connecticut for the shipping industry, for the building industry, and not to mention now, as I’m learning more about the chestnut, so important for our ecology. Representing a quarter of the trees that really were across the entire northeastern seaboard, the chestnut provides a really unique and important ecosystem for things like tree frogs, for different types of bacteria, for different types of fungus that are very beneficial to the ecosystems in the Northeast and again down Appalachia as well. So the chestnut is very important for finances. I guess for the financial future and thinking about agriculture of the Northeast, but also for the ecosystem around and supporting their giant trees, and so they really represented a huge part of what our forests were up until the 1920s and 1930s.

Tan Deleon
Okay, Susanna.

Susanna Keriö
Yeah, so related to Rachel’s story, as she mentioned, chestnut used to be really important, but unfortunately, there was this disease that was initially discovered in 1904 in the Bronx Zoo in New York. These were orange cankers that were sporulating on the tree, and it turned out that it is a fungal pathogen that is causing these cankers on the tree. So essentially, when the trees are affected by chestnut blight, these cankers form on the tree, and these cankers end up girdling the tree, which then blocks the transport of nutrients in the tree, and this causes the leaders or the stems of the trees to die back. But when the main stem of the tree dies back, these trees actually sprout back from the stumps, but then eventually, these stump sprouts that develop will also get infected by the fungus, and then these newly emerged sprouts also die back. And this kind of cycle is a vicious cycle that just keeps repeating, which has then resulted in the situation where the chestnut trees are no longer able to reach the dominant canopy layers in the forests, because these trees really used to be 100-foot-tall trees, very amazing large trees, sometimes also called the redwoods of the east. So now, with the fungal pathogen here, these trees are no longer able to grow very tall. They are not able to produce flowers, and if they are not producing flowers, they are no longer producing the seeds or the nuts. Which means that there is no more. Regeneration of the species: no more new little chestnut seedlings emerging from the forest floor, and this has essentially resulted in the situation where the American chestnut is now functionally extinct.

Tan Deleon
Oh man, yeah. So you have the effect agriculturally of the chestnut, but then you also have the monetary effect of the chestnut, like being used in, as Rachel mentioned, in her home. So, how did the blight come about for the chestnut?

Susanna Keriö
That’s a really good question. So, the importation of chestnut seeds has been happening to the United States since the 1850s, and along with these seeds that have been imported from Asia and Europe as well, they unfortunately carried the fungal pathogen. So these seeds don’t show the symptoms of the disease, but they still carry the fungus — the mycelium of the fungus — that is then able to cause the disease. And initially, these seeds were of Asian origin, which means that they have high resistance to the pathogen because they have co-evolved with this fungus, and they have resistance to the disease, which means that these Asian trees do not develop the cankers to the extent that they develop on the American chestnuts. But once the pathogen came into contact with the American trees, they turned out to be highly susceptible to this fungal pathogen, so the Asian trees carry the key, or they carry resistance to the disease, whereas the American trees are highly susceptible to the blight.

Tan Deleon
Okay, okay, that that that kind of reminds me – of I don’t know if you guys are familiar – but with phylloxera in with with viticulture in in France, and I guess it was in that scenario. The French vines were being attacked by this aphid, and I guess the only way they were able to – if I have this right in my head – the only way they were able to mitigate the death of all these vine plants was to graft an American rootstock with the French vine because the American rootstock was so resilient to this aphid. So is that approach similar here for chestnut blight, or is that not even a starter? Is that a non-starter?

Susanna Keriö
Rachel, do you want to comment on this because it relates to the breeding work that you guys are working on?

Rachel Jeffrey
Yeah, as a volunteer, I work a lot with the American Chestnut Foundation and the Connecticut Chapter specifically of the American Chestnut Foundation, and our main goal is to keep the genes alive. And that sounds weird. Obviously, we want to save trees, but we’re really not saving trees. We’re thinking about hundreds of years from now. How can we preserve the genes of the American chestnut so that we could have an American chestnut again someday? So the way that we do that to preserve kind of what the American chestnut could be in the future, and is right now, is diversity, where we try to keep enough genetic diversity alive so that there might be some opportunity in the future for the American chestnuts that are in the wild to be able to reproduce with each other. Right now, because there are so few trees out in the wild, and at places like the library in Old Lyme, there are so few trees alive that they can’t pollinate each other. So we do a lot of work to facilitate pollination of specific trees that we want to keep the genetic background for. You talked a lot about the stump sprouts, Susanna, and I maintain an orchard at my property at home with 30 trees, and they’re each from three different mother backgrounds. One of them is from stump sprouts from a tree in Roxbury that is considered one of the most significant, oldest American chestnut trees that we know of, at least in Connecticut, and so we try to keep that diversity alive so that we can be selective in the breeding strategies to try to encourage trees that somehow are resistant to the blight. There are also some other things that we’re trying to work on that deal with the way that roots rot and are susceptible to another disease. So we really try to keep diversity in the breeding population and keep these trees alive long enough so that we can collect nuts and have some specific breeding partners so that they are breeding with other American chestnuts. So we do controlled pollination as well, which is really fun. We climb up on ladders, and we cover up the flowers of the chestnuts that we’ve identified genetically as being very important for maintaining the genes of the American chestnut, and we cover the flowers up with paper bags. Basically, we want them to be biodegradable and safe for the environment, but they protect the flowers so that they don’t get pollinated by other European or Asian background chestnuts that might be in the area, and then we go, and we use pollen that Susanna often provides us with— pollen that is specific for different trees. We collect pollen from across the state, from across all of New England, and we do this controlled pollination in a way that we can then know the background and the lineage of the nuts we produce, and we collect those nuts and try to keep that diversity going.

Tan Deleon
Okay, so the essence of the orchard is to maintain diversity, and you want to keep it because, years from now, we want to have an American chestnut, or the ability to grow American chestnuts, right? Okay, I just want our listeners to understand the importance and, really, the reason why you guys are going through such great efforts to keep this wonderful tree alive for future generations. So, Susanna, can you describe your research on biological control of chestnut blight to support the American chestnut restoration?

Susanna Keriö
Certainly. So the research that I’m conducting now on the biological management of chestnut blight is a research project started in 2025, and it is supported with funding from the United States Forest Service. And our goal for this project, the long-term goal is to build capacity for biological control, chestnut blight, and chestnut management in Connecticut and in New England to support the health of existing American chestnut trees and also the re-establishment of the species in the forests. And in very simple terms, what we are doing with this project is that we are trying to give the fungal pathogen a viral disease, which slows down its growth. And actually, our project name is Blight Busters, so it’s a very accurate description of what we are trying to achieve. We are trying to bust the blight. Yeah. Yeah. So, how we are achieving this is we are utilizing double-stranded RNA viruses called hypoviruses, which infect the pathogen and they slow down the growth of this pathogen, and in this case, these viruses are actually the good guys. You think about viruses, you come up with these associations with COVID and HIV and all this bad stuff. Actually, in this case, we are delighted to have these double-stranded RNA viruses, which actually infect the fungal pathogen and make the life of the pathogen a little bit more miserable, and in turn, the life of the American chestnut tree becomes a little bit easier.

Tan Deleon
That’s pretty brilliant. So the hypovirus will only attack the fungal pathogen. It won’t – there’s nothing else that it can do to, I guess, other cells in the tree?

Susanna Keriö
Yes. Yeah. These hypoviruses are very specific to the fungal pathogen, and to my knowledge, they have not been found in any other species outside the Cryphonectria genus. So this is really good. We wanted to be specific to only the pathogen that we are trying to get rid of.

Tan Deleon
I guess, how did you come to the realization that you needed to use hypoviruses? I’m assuming you didn’t create the hypovirus; it was something that was already in nature that you just were able to leverage?

Susanna Keriö
Yes. So actually, there are very long roots or a long history of research on hypervirulence in terms of blight management at the Connecticut Agricultural Experiment Station. The station scientists were actually among the first in the United States to begin researching this topic, and initially, they studied hypoviruses, or the phenomenon of hypovirulence, which means a reduced capacity to cause disease, first discovered in Europe in the 1950s in Italy. So a discovery was made. In chestnut trees that had these cankers, they started healing, and then the question became: what is in these cankers that is causing the spontaneous healing of these cankers? And it turned out to be a virus. And then it was realized that it is actually something transmissible that can transmit from one canker to the other; the interest became to develop this into a method to manage the blight by using these hyperviruses. And then in the 1970s, these viruses, or these hypervirulent strains, these blight strains that carry these viruses — were imported to the United States to the Connecticut Agricultural Experiment Station, and in 1976, a field experiment was actually established in the research farm of the Connecticut Ag Experiment Station in Hamden to study the potential of these hypervirulent strains in chestnut blight management.

Rachel Jeffrey
Susanna, how are you going to introduce this? I’m so curious. How are you? How will you plan to introduce this hypovirulence to the chestnut tree?

Susanna Keriö
Yeah, that’s a really good question. So we actually use these slurries or fungal smoothies, which contain both the fungus, which carries the virus, and yeah, and the growth media. And then this slurry is applied to the cankers, and then from this slurry, the virus gets transmitted into the cankers, and then once the virus becomes established in the mycelium, which is colonizing the canker, and once the fungus starts sporulating, the virus also gets transmitted into the spores. And when the spores, which also cause the infection from one tree to the other, travel from one tree to the other, so does the virus. So if we are able to successfully establish this virus in these cankers, and the fungus in the cankers is sporulating, then this means that the virus spontaneously transmits from one tree to the other, which would really form the basis of sustainable biological management of chestnut blight.

Tan Deleon
So it’s basically just like a, it’s like a like you’re putting a lotion, like a lather on the canker. Is that when you say the slurry?

Susanna Keriö
Yeah, in a way. Yeah, in a way. Or then a more sophisticated approach: you make a little hole in the bark, and you insert a plug of the mycelium of the hypervirulent isolate that carries the virus. And then, if these fungal strains that are in the canker and in the plug of mycelium are compatible with each other, then the transmission of the virus will happen, and it will become established in the tree. And then, once the fungus sporulates, the spores will also transmit the virus from one tree to the other.

Tan Deleon
Rachel, go ahead. You had a question you were going to ask.

Rachel Jeffrey
Thank you. So, we at the American Chestnut Foundation try a lot of things. It’s interesting for me as a scientist to see how people do science in different ways, and a lot of times we are just going out and trying things. So one of the things we do often is we will go out and make a mud paste on the cankers that we’re finding. And so one strategy that we’ve used is that, as soon as we see the canker forming on young trees, we do go out and put just dirt from the soil, hoping that it’s going to stimulate the immune system, hoping it’s going to introduce some response to the tree that it can then fight off the fungus. But it sounds like we could marry those two strategies and easily just wrap saran wrap with your super paste of the hypovirulence. So,

Susanna Keriö
Yeah, that’s the dream. There are several approaches that, you know, a combination of all these different approaches: the breeding program, conservation of the germplasm, the hypervirulence, and mud packing. All these approaches combined may hold the key to successful restoration of the American chestnut.

Tan Deleon
It’s fascinating because, I guess, if you asked just like a layperson, right, they wouldn’t expect that doing what you’ve just suggested would even be an approach, right? But it just goes to show how closely related… like we’re living things; trees are living things. Like, it may not move or go anywhere; the associations are very similar, and it’s really fascinating. Just to think, because the bark of the tree and the human skin, right? If I need to moisturize, I’m gonna put lotion on or something, right? And it really is fascinating. So that’s, I really hope it works. And interested to see what happens down the road with this work. So Rachel, you had mentioned that you have an orchard where you guys are doing this type of pollination. Is there an easier way? Because you were talking about climbing a ladder. Are there easier ways to do it so you’re able to have faster replication, or is that not, or do you just need to do it the natural way because you don’t want to alter a gene or something for the diversity that you had mentioned before?

Rachel Jeffrey
So, is there an easier way? We’re hoping to produce nuts on the tree, and so for us to produce, or for the tree to produce nuts, it has to be pollinated by another chestnut tree. So, what we are doing is choosing who will get to produce the nut… In terms of a faster way – the ladders, it works. Actually, we have a truck with a hydraulic lift. We get a lot of help from UI, the electric company, to go to certain trees in the state to both pollinate and collect nuts, but the reality is, this is a long project. This is a long – in my lifetime, in my children’s lifetime, will they see a difference? Perhaps, but maybe not. And so, I think that’s something so different that we need to think about with these ecology and forestry questions. How can we do it in a way that is careful and sustainable, but it’s not fast. The ladders do work. I have a lot of students that have helped me. Some Southern students have helped me with these projects, and they’re young, they’re fit, they’re happy to be up, and it’s always hot. It’s always 100 degrees and sunny. And the trees, because they are so tall, most of our trees aren’t 70 feet tall anymore. But some of them are. Some of them are actually so tall that we have a giant slingshot that we use for one of our projects to pollinate. So we actually slingshot up a rope and lift up some buckets filled with flowers from a tree from 100 miles away. So it is a slow project; it’s a slow process, but we really want to be thoughtful and careful about this, about how the tree naturally will grow and how the tree naturally will produce these seeds, these nuts, and then we eat 90% of them that just fall on the ground that we can’t use.

Tan Deleon
Oh, okay. So you’d mentioned you guys select. So what’s the process of selection?

Rachel Jeffrey
So there are many different processes for selection. The strongest, in my opinion, as a cell and molecular and biochemistry background person, is the genetic background of these trees. And in collaboration with lots of different labs across the Northeast, there is a database of the genomes of specific trees. So if I walked up to a tree in Hamden, we would know its genome, and we would know that it has particular traits based on that genome that we would be wanting to keep in terms of the conservation of the American chestnut tree.

Tan Deleon
Okay, and so just one more to you, Rachel. So, if the public is interested in trying to engage with the Connecticut chapter of the American Trestle Foundation, how can they support your efforts?

Rachel Jeffrey
You can find us at tacf.org. You can look for CT TACF. There are so many different ways that we are looking for volunteers. If you want to put on your long pants and your gloves and do some weeding. If you want to hike across different water properties and help us collect nuts. If you want to help with mapping, if you like to use drones, we have different drone projects that we’re thinking about for scanning and finding new American chestnut trees that might be in bloom that we didn’t ever know existed. So there are lots of fun ways for people to get involved. They all involve being outside in the summer in Connecticut. Again, do your tick check, get some sunscreen on, and please join us. We have a lot of volunteer and fun volunteer activities. Shucking nuts. The chestnut burrs themselves are little tiny porcupines, so we all get around and use tools and wear gloves to shuck all of the nuts that we will use for propagating seeds across the state. But then again, we also roast the other bunch of them and eat them together. So it’s a fun group of people that really care about lots of different levels of Connecticut. What does it look like to be sustainable as a forest and as a tree in your downtown? A tree that’s next to your library. A tree that’s where you walk on the sidewalk with your family. Lots of different ways to engage and think about what communities can do to interact with their environment.

Tan Deleon
Yeah. Now, can they also help with the pollination, getting in the bucket trucks?

Rachel Jeffrey
Yeah, yeah. You can be part of the bucket brigade team. I have one of my favorite students – I shouldn’t have a favorite student – but I do. She went on to work with TACF on it. She was employed by them after doing different database entries of different GPS coordinates for the trees, and then we have a special column for which ones require the bucket truck.

Tan Deleon
I like it. I like it. So, Susanna, can the public become a blight buster? Can anyone volunteer to be a blight buster?

Susanna Keriö
At least you can definitely engage by participating in some of the CAES activities that we organize. So every year, the Connecticut Agricultural Experiment Station organizes the Plant Science Day, which is a science outreach event held at the Lockwood Farm in Hamden. It’s organized every August, on the first Wednesday of that month, and you have the chance to meet the scientists and learn about the research that we do at the ag station. We would love to have you there. Additionally, if you are really excited about chestnut trees and would like to see some really cool specimens of chestnuts, I would highly recommend visiting Lockwood Farm because we have in that farm the most amazing collection of different kinds of chestnut species and hybrids that you can imagine. These are some of the finest specimens of chestnuts you can find in the United States. Lockwood Farm is located in Hamden and is open to the public from 8:00 a.m. to 4:00 p.m. on the weekdays, Monday through Friday. Yeah.

Tan Deleon
Yeah. Thank you for that. So just this just takes me back to chestnuts roasting on an open fire, right? So do the different variations taste different too? I don’t know if you’ve had a chance to eat any of them, but do they taste different than what we’re normally used to buying in the store?

Rachel Jeffrey
I think they do. They’re annoying, though. The American chestnuts are much smaller. Their fat content is higher. They’re more nutritious. They have a different amino acid profile, which makes them a really wonderful food source for the indigenous peoples of North America who lived on them for 1000s of years. They’re really tasty, but they are annoying because you do the little cutting and the peeling, and then you just get about half the size of what you might see in the grocery store for a nut. But they are very tasty.

Tan Deleon
So you gotta savor all your hard work. All right, no, thanks for that. I was just curious about that. On behalf of CASE, I want to thank our guests, Rachel Jeffrey and Susanna Keriö, for joining us today to provide our listeners with insights into their work in chestnut restoration across Connecticut. Listeners, I encourage you to subscribe to this podcast on Apple Podcasts, Spotify, Amazon Music, or YouTube. Visit the Academy’s website at ctcase.org to learn more about our guests, access show notes with additional resources, read the episode transcript, and sign up for the CASE Bulletin. Thanks again to our guests. It has been a pleasure to talk to you today. This was really fun. Thank you, guys.

Rachel Jeffrey
Thank you.

Susanna Keriö
Thank you.