Prescreening slash pine and Cronartium pedigrees for evaluation of complementary gene action in fusiform rust disease

Single-urediniospore cultures of the fusiform rust fungus were used to inoc ulate seedlings from 10 full-sib families of a five-parent slash pine diall el at two different times in 1994. The presence or absence of fusiform rust galls was recorded for each inoculated seedling at 9 months postinoculatio n, and percent infection levels for each family-inoculum-time combination w ere used for detecting differences among host families and fungal cultures and for identifying differential interactions. The existence of differentia l interactions between two or more fungal cultures and two or more host fam ilies verifies that complementary gene action does exist in this pathosyste m. Some host families may be excluded from more detailed interaction studie s on the basis of their redundancy and lack of participation in differentia l interactions.