As our natural food supply faces threats from climate change and habitat loss, crop wild relatives have been a recent research darling. 

Crop wild relatives can provide genetic diversity that modern agriculture lacks, offering better resistance to disease and pests. Much research on these wild species has taken place in distant locales, like Kyrgyzstan, which is home to the wild relatives of popular produce like apples, plums, cherries, and almonds. But native North American fruits, like pawpaws and persimmons, are ripe research, too. 

“People always talk about crop wild relatives in exotic places and forget we have them here in our own backyard,” said Missouri Botanical Garden Scientist Emily Warschefsky. 

Warschefsky and colleagues at San Diego Botanic Garden and Botanic Gardens Conservation International are working to protect those species by building a collaborative conservation network focused on North American wild relatives of fruit and nut trees. 

The role of crop wild relatives in the food supply 

Crop wild relatives are wild plant species related to crops commonly consumed by humans. Preserving these unique species is important in maintaining biodiversity, but also could also play a crucial role in food security. 

Since they are genetically different from cultivated crops, their diversity can be useful in breeding programs. With trees, wild species can be used as rootstock to help grow cultivated nuts and fruits. All of this is especially important as we face an uncertain future. 

“We don’t know what future challenges we’ll be facing in terms of climate change and disease,” Warschefsky explained. “We want to make sure we are conserving as much diversity as possible so we can find individuals to help as we face future challenges.”  

Habitat loss is another challenge, particularly for large tree species. Experts agree trees are likely to play a large role in the future of the crop system, Warschefsky explained, because they are perennial and can often withstand climate impact better than annual crops. 

The lack of genetic diversity in agriculture has the possibility to present a host of problems, too. Tree species used in commercial farming are all grafted and genetically identical, which makes them more susceptible to disease.   

Mind the gap 

A 2019 study outlined a road map for conservation and use of America’s crop wild relatives Records for ex situ conservation, or conservation that takes place in a controlled setting like a botanical garden, a increased by 200 percent for 16 taxa as a result of that project. 

Warschefsky and colleagues, including Senior Director of Science and Conservation at San Diego Botanic Garden and paper author Colin K. Khoury, want to build on that success by creating a network of botanical gardens and other relevant parties, like the USDA, focused on conserving 90 taxa and targeting 10 genera, five fruit trees and five nut trees.  

Already, they have established a network with more than 70 participants.  They are working to assess ex situ conservation collections by surveying botanical gardens to see where the targeted species exist in living collections. They will use that information to find gaps where these species aren’t currently growing but could be added to living collections in the future. 

“A gap analysis helps us prioritize collecting efforts for conservation projects,” Warschefsky explained. “It allows us to see where individuals that are in ex-situ conservation collections were originally collected from in the wild, and to identify geographic areas that we don’t have collections from.” 

Targeted Trees 

North America has an expansive list of crop wild relatives including beans, corn, blueberries, cranberries, cotton, onions, pumpkins, and much more. For this project, Warschefsky and colleagues narrowed down the focus on woody plants. Still, that left 300 woody crop wild relatives native to the United States as possibilities. The group decide to look at factors including current importance of the crop and its cultivated relatives, as well as historic and traditional uses of the species. They landed on a list of five fruit and five nut trees: 

Fruits 

1. Asimina (Pawpaw): Sometimes called America’s forgotten fruit, pawspaws are the largest edible fruit in North America. They are native to Missouri. 

2. Diospyros (Persimmons): North American persimmons produce smaller fruits than Asian persimmons, but their fruits can be used in syrups, jellies, ice creams or pies.  

3. Malus (apples) The apples we eat and use for baking trace their roots back to Central Asia, but crabapples, native to North America, could provide needed genetic diversity or rootstock to commercial apple crops. 

4. Prunus (plums and peaches) Like apples, the plums and peaches you see at the grocery store are descendent from wild relatives in Central Asia. Wild plums and peaches in North America, however, are edible and were traditional food in many indigenous cultures. 

5. Persea (avocado) Hass avocados, the most commercially popular variety of avocado, are all genetically identical. Genetic diversity of avocado wild relatives in Texas could prove useful for the future of commercial farms. 

Nuts 

1. Carya (pecans) The United States produced 80 percent of the world’s pecans. Most of those are Carya illinoinensis, commonly called hardy pecan, but more than a dozen other carya species produce edible seeds.

2. Corylus (hazelnut) While the majority of hazelnuts we consume come from Turkey, native American Hazelnuts are grown the Midwest, East, and Southeast of the United States and Canada. The American Hazelnut, Corylus americana, is a Missouri native.
3. Pistacia (pistachio) The only pistachio tree native to North America, pistacia texana is related to the common pistachio, Pistacia vera, that we eat, which is native to Asia.
4. Castanea (chestnut) People living in North America have a long history of consuming castanea fruit. Blight killed off many of the popular Ozark chinquapin, Castanea ozarkensis, in the 1940s but the tree has seen. a recent resurgence, with more people opting to plant these trees in their native range.
5. Juglans (walnut) The black walnut, a Missouri native, is already one of of the most popular species used in cultivation. Other walnuts native to North America

 
Collaboration is key 

After completing the first phase of the project, Warschefsky will delve deeper by doing population genetics in some species to ensure they are conserving genetic diversity, answering lingering taxonomic questions, and determine the conservation status of threatened species.  

They’ll also move forward with in situ conservation, establishing conservation areas dedicated to crop wild relatives that they hope can be a model for the future. 

Collaboration among this newly-formed network is essential in the success of conservation, Warschefsky said.  

 “It’s not going to be one institution that can conserve a species. Ultimately, we hope this community of people will be able to coordinate conservation,” she said.  

Catherine Martin
Senior Public Information Officer

Many thanks to Emily Warschefsky, Associate Scientist in the William L. Brown Center, who collaborated on research for this blog. Also thanks to Botanic Garden Conservation International, US and the United States Botanic Garden for the support of this project