Mutations Affecting Perithecium Development and Sporulation inMagnaporthe grisea

Abstract

We characterized two spontaneous developmental mutants of the heterothallic AscomyceteMagnaporthe grisea.The first mutant, isolated from finger millet isolate OG2, sporulated abundantly when grown on artificial medium. Compared to wild type, the sporulation rate of OG2-HSP was 10 times higher on artificial medium and 3 times lower from infected leaves. OG2-HSP was unable to develop perithecia in crosses (female sterile) and behaved only as a male. These two characters always cosegregated as a single gene named HSP1 (high sporulation on plates). A second spontaneous mutant, isolated fromM. griseafinger millet isolate OG5, differentiated perithecia in homokaryotic culture. These perithecia did not contain asci or ascospores, whatever their developmental stage. This mutant was still hermaphroditic in crosses with strains of opposite 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 bothsfp1andhsp1,all progeny sporulating abundantly on plates (Hsp) was female sterile and unable to develop sterile perithecia in homokaryotic culture, showing thathsp1-1was epistatic tosfp1-1.These mutants will be particularly useful to study the control of sporulation and perithecium development inM. grisea.