100 years ago, American Chestnut trees grew up and down the East coast. Great wood, nommy nuts, awesome! Unfortunately, an epidemic of an Asian fungus, Cryphonectria parasitica, basically wiped them out.
Asian Chestnut trees are resistant to the Asian fungus, so theoretically we could ‘save’ the American chestnut industry by planting Asian trees here… but they dont have the same beneficial features of the American species.
How can we save the American Chestnut?
Solution 1 (in progress)– Keep crossing Asian Chestnut trees with American chestnut trees until you get a tree with American characteristics and Asian fungus resistance (or take a shortcut and make a GMO).
Solution 2– While Solution 1 is going, give currently surviving American Chestnut trees a therapeutic vaccine. Therapeutic vaccines dont prevent infection like the vaccines you are familiar with (like MMR, which prevents measles/mumps/rubella), they are given post-exposure to limit pathogenesis.
American Chestnut trees with Asian fungal lesions are given a ‘vaccine’ in the form of more fungus… but this fungus is infected with a fungal virus, hypoviridae. The virus goes on to infect all of the fungus infecting the tree, weakening the fungus so the trees immune system can kill it off!
You cant use virus/fungus as a prophylactic vaccine, as plants dont have an adaptive immune system like we do (they dont ‘remember’ pathogens theyve seen before). But this therapeutic ‘vaccination’ strategy can keep the American Chestnut population alive long enough for the breeders to find a permanent solution!