VIRULENCE OF GIBBERELLA-PULICARIS ON POTATO-TUBERS AND ITS RELATIONSHIP TO A GENE FOR RISHITIN METABOLISM

The ability of field strains of Gibberella pulicaris (Fusarium sambucinum) to cause dry rot of potato tubers is related to their ability to metabolize the potato phytoalexin rishitin. All highly virulent field strains studied to date have proven tolerant of and able to metabolize rishitin. Preliminary genetic analysis of one potato-pathogenic field strain, R-6380, suggested that multiple loci might confer rishitin metabolism and that not all of these loci are associated with virulence (A. E. Desjardins and H. W. Gardner, Mol. Plant-Microbe Interact. 2:26-34). To investigate these hypotheses, four phenotypically unique meiotic products of a tetratype ascus from a backcross to strain R-6380 were crossed to strains that were low in rishitin tolerance, rishitin metabolism, and virulence. Tetrad progeny from all four crosses were analyzed for these traits. This genetic analysis indicated that rishitin metabolism in strain R-6380 is controlled by genes at two or more loci but that high virulence on potato is associated with only one of these loci, designated as Riml.