MAGNAPORTHE-GRISEA PATHOGENICITY GENES OBTAINED THROUGH INSERTIONAL MUTAGENESIS

We have initiated a mutational analysis of pathogenicity in the rice b last fungus, Magnaporthe grisea, in which hygromycin-resistant transfo rmants, most generated by restriction enzyme-mediated integration (REM I), were screened for the ability to infect plants. A rapid primary in fection assay facilitated screening of 5,538 transformants, Twenty-sev en mutants were obtained that showed a reproducible pathogenicity defe ct, and 18 of these contained mutations that cosegregated with the hyg romycin resistance marker. Analysis of eight mutants has resulted in t he cloning of seven PTH genes that play a role in pathogenicity on bar ley, weeping lovegrass, and rice. Two independent mutants identified t he same gene, PTH2, suggesting nonrandom insertion of the transforming DNA. These first 7 cloned PTH genes are described.