Relationships of Genetic Background Among Pyricularia Species, the Blast Pathogens on Gramineous Plants

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Seeds and Pyricularia strains from Panicum miliaceum (Pm) and Setaria itarica (Si) collected from a mountainous area of Japan were used in order to examine the relationships of differentiation of pathogenicity.l. Host range : Seven tribes of gramineous plants were utilized for inoculation tests. 1) Pm-strain attacked eighteen species among twenty seven. No pathogenicity was found against rice, Si and Eleusine coracana (Ec). No differentiated races were detected to Panicum miliaceum from Japan. 2) Si-strain attacked fourteen species among thirty one. There were races to Setaria itarica from Japan and China and no pathogenicity against rice, Pm and Ec.2. Mating type : Standard isolates of mating types A and a of Ec were crossed with isolates of Pm and Si-strains to decide the mating type. 1) Pm-strain was classified into a-type (26 isoiates out of 39 isolates) and no A-type. 2) Si-strain was six A-type and nine a-type.3. Mating ability : 1) Pm-strain was mated with Ec-strain, but ascospores were incomplete. Pm-strain was not mated with either rice-strain or Si-strain. 2) Si-strain was mated with both rice -strain and wheat-strain and some ascospores were fertile. Laggingchromosomes appeared 27 to 46% in the cross between Si-strain and Ec-strain and 24 to 35% in the cross between Si-strain and wheat-strain.Based on these results, Pyricularia from Pm and Si has differentiated into two strains (forma specialis), though both plants have been raised in the same area.