Genetic relationships between fertility and pathogenicity and virulence to rice in Magnaporthe grisea

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Abstract
The genetic relationships between fertility and pathogenicity and virulence to rice in Magnaporthe grisea (Hebert) Yaegashi & Udagawa were examined in four initial-generation and two second-generation families. Two isolates of M. grisea, highly virulent to rice, were crossed with fertile isolates that are pathogenic on weeping love-grass (Eragrostis curvule) and goose-grass (Eleucine indice). Approximately 30 progenies from each of the four initial-generation families were evaluated for mating type, fertility, pathogenicity, and virulence to rice differential cultivars. Most of the progenies were either nonpathogenic to rice or produced intermediate infection types. The expected 1:1 segregation for female fertility was not observed in progenies of the initial-generation families. Two highly virulent isolates, and one fertile isolate that produced small grey flecks on one rice cultivar, were selected from one of the initial-generation families as parents for two second-generation families. Nearly one-third of the progenies from one of the second-generation families were highly virulent to rice. Female fertility segregated in the expected 1:1 ratio, independent of mating type, in both families. Mating type, female fertility, and pathogenicity to rice segregated randomly; however, progenies highly virulent to rice were exclusively mating-type A and female sterile.