When
inoculated back into American chestnut, white cultures give smaller cankers
than yellow cultures. They are
hypovirulent. In addition, the virus
causing whiteness
and hypovirulence can move from a white to a yellow culture. Here, the center canker, caused by a yellow
culture, started out larger than those caused by the white cultures, but
then stopped expanding. White
hypovirulent cultures were isolated from it, and they were the
original yellow culture infected with the virus from the original white culture.
White culture
Yellow culture
White culture