•Canker size is a good metric of resistance to colonization.  We have been unable to measure resistance to infection, which may be a defect in the program
•Canker size is strongly dependent upon environmental conditions, which can be manipulated experimentally
•This study gave results opposite of what was expected.  It was easier to distinguish the intermediate blight resistance of Chinese x American F1s from susceptible American chestnut when trees were young, and easier to distinguish intermediate resistance from blight-resistant Chinese chestnut when trees were old.
•However, trees with low to intermediate levels of blight resistance do not survive inoculation until they are three years old, so need to be screened when older, while more resistant trees can be screened when young, occupying less space and time, but not as young as I had thought.