VIEW ARTICLE

Genetics

Genetic Analysis of Virulence in the Rice Blast Fungus Magnaporthe grisea. Hei Leung, Associate plant pathologist, International Rice Research Institute, P.O. Box 933, Manila, Philippines; Emerlito S. Borromeo(2), Marichu A. Bernardo(3), and Jean L. Notteghem(4). (2)(3)Research assistant, and Research aide, respectively, International Rice Research Institute, P.O. Box 933, Manila, Philippines; (4)Plant pathologist, Institute de Recherches Agronomiques Tropicales, 34032, Montpellier, Cedex, France. Phytopathology 78:1227-1233. Accepted for publication 5 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1227.

Crosses between rice isolates of Magnaporthe grisea were made to determine the genetic control of virulence to rice. A cross between a hermaphroditic rice isolate, Guy 11, and a laboratory strain 2539, yielded more than 50% viable ascospores. Random spore and tetrad analysis showed that two loci, Pos1 (pathogenicity on Oryza sativa) and Pos2, were involved in conditioning virulence to rice lines 51583 and Sha-tiao-tsao. A buff mutation was epistatic to virulence. Fertility and ascospore viability were low in crosses between field rice isolates. In a cross between two rice isolates, Guy 11 and CH 104-3, only 10% of the ascospores was viable, but all progeny were virulent to 51583 and Sha-tiao-tsao. From this cross, we identified two different loci, Pos3 and Pos4, controlling virulence on rice lines K59 and Kinandang Patong, respectively. Fertility and virulence were maintained in progeny recovered from F₂ and F₃ generations. Joint segregation analysis showed an excess of parental types with respect to virulence. This might reflect genetic linkage of virulence genes or segregation of other genetic factors epistatic to virulence.