GENETIC-ANALYSIS AND RAPID MAPPING OF A SPORULATION MUTATION IN MAGNAPORTHE-GRISEA

A developmental mutation causing abnormal conidium morphology and a reduction in sporulation was found in the rice blast fungus, Magnaporthe grisea. The conidium mutant, Con(-), was recovered among survivors of an electroporation experiment in which germinated conidia of strain Guy11 were subjected to an electrical shock of 3,000 V/cm. Instead of producing a cluster of four or five conidia sympodially borne on a conidiophore, the Con(-) mutant produced an aerial hypha bearing an elongated terminal conidium (4 x 50 mu m). The growth rate and sporulation of the Con(-) mutant on culture media were 73 and 2.3%, respectively, of that of the wild-type Guy11. Pigment formation in the mutant was reduced and delayed for at least 7 days relative to that of the wild-type strain. Random spore and tetrad analysis showed that the Con(-) phenotype was controlled by a single gene (Con1). Delayed pigment formation co-segregated with the Con(-) phenotype. The Con(-) strains did not produce normal appressoria on a siliconized slide or onion epidermis and were nonpathogenic on rice lines susceptible to the wild-type parent. Double mutants obtained from crosses between Con(-) strains and a previously described spore morphology (Smo) mutant had a Con(-) phenotype, indicating that the Con(-) mutation is epistatic to Smo(-). As a first step toward physical isolation of the Con1 gene, bulked segregant analysis was employed to rapidly generate DNA markers flanking the Con1 gene. A linked marker 7 cM away from the Con1 locus was obtained.