Fusiform rust, a disease of southern pines, significantly impacts productivity, especially in intensively managed plantations, directly through pine mortality and growth loss and indirectly through added costs of disease control, replanting and site deterioration. In extensive areas of Florida, fusiform rust is the major factor limiting production in pine plantations. In the late 1950's, research began on the selecting and testing of southern pine for rust resistance. Rust resistant pine genotypes were found and forest plantings with half-sib progeny from resistant parents showed significant improvement. It is of critical importance to determine the stability of resistant pines, temporally and spatially, since it is known that multiplication of virulent pathotypes in response to selection pressure by resistant hosts can overcome resistance in other rust diseases.
Recent developments make possible new approaches to study host-pathogen interactions.
It is now possible to challenge known genotypes of the host with known pathotypes of the fungus. Much of this research on selecting and testing trees for disease resistance is directly transferable to international programs and I am involved in research programs in South America, especially Brazil, where we are attempting to select, test and breed for resistance to a fungal disease in cacao, the tree from which we get the beans for chocolate manufacture.