MUTATIONS AFFECTING PERITHECIUM DEVELOPMENT AND SPORULATION IN MAGNAPORTHE-GRISEA

We characterized two spontaneous developmental mutants of the heteroth allic Ascomycete Magnaporthe grisea. The first mutant, isolated from f inger millet isolate OG2, sproulated abundantly when grown on artifici al medium. Compared to wild type, the sporulation rate of OG2-HSP was 10 times higher on artificial medium and 3 times lower from infected l eaves. OG2-HSP was unable to develop perithecia in crosses (female ste rile) and behaved only as a male. These two characters always cosegreg ated as a single gene named HSP1 (high sporulation on plates). A secon d spontaneous mutant, isolated from M. grisea finger millet isolate OG 5, differentiated perithecia in homokaryotic culture. These perithecia did not contain asci or ascospores, whatever their developmental stag e. This mutant was still hermaphroditic in crosses with strains of opp osite mating type. Genetic analysis showed that this mutant character was controlled by a single gene named SFP1 [self-formation of sterile perithecia]. In crosses heterozygous for both sfp1 and hsp1, all proge ny sporulating abundantly on plates (Hsp) was female sterile and unabl e to develop sterile perithecia in homokaryotic culture, showing that hsp1-1 was epistatic to sfp1-1. These mutants will be particularly use ful to study the control of sporulation and perithecium development in M. grisea. (C) 1997 Academic Press.