Genetic Analysis and Rapid Mapping of a Sporulation Mutation in Magnaporthe grisea. Zhixin Shi. Department of Plant Pathology, Washington State University, Pullman 99164-6430 U.S.A. Hei Leung. Department of Plant Pathology, Washington State University, Pullman 99164-6430 U.S.A. MPMI 7:113-120. Accepted 18 October 1993. This article is in the public domain and not copyrightable, It may be freely reprinted with customary crediting of the source. The American Phytopatho-logical Society, 1994.

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 elec-troporation 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 (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 (Conl). Delayed pigment formation co-segregated with the Con" phenotype. The Con- strains did not produce normal appresso-ria 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 Conl gene, bulked segregant analysis was employed to rapidly generate DNA markers flanking the Conl gene. A linked marker 7 cM away from the Conl locus was obtained.