VIEW ARTICLE

Genetics

Enzyme Polymorphism and Genetic Differentiation Among Geographic Isolates of the Rice Blast Fungus. Hei Leung, Former graduate research assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of the first author: Department of Plant Pathology, International Rice Research Institute, Los Baņos, Philippines; P. H. Williams, professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 76:778-783. Accepted for publication 24 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-778.

Polymorphisms in 12 enzymes were examined among 335 rice isolates of Magnaporthe grisea from 12 rice-growing regions of the world. Six electrophoretic types (ETs) were found. Ninety-five percent of the 335 isolates belonged to two common ETs. All isolates were monomorphic at 16 of the 18 putative enzyme loci. When isolates were pooled as a single population, the proportion of polymorphic loci (P) was 0.11 with an average gene diversity (H*) of 0.03. In contrast, a sample of 34 nonrice isolates of M. grisea from several gramineous hosts showed more allelic variation (P = 0.5, H* = 0.21). Among the rice isolate populations, geographic differentiation was observed at the lactate dehydrogenase-1 (Ldh1) locus, where the distribution frequencies of a functional allele (Ldh1¹⁰⁰) and a null allele (Ldh1ⁿ) appeared to follow a north-south geographic trend. However, because there was also a strong association between Ldh1¹⁰⁰ with japonica rice and Ldh1ⁿ with indica rice, it was not certain whether the distribution of the Ldh1 alleles was influenced by climatic factors or by rice geographic races.