Development of EST-derived CAPS and AFLP markers linked to a gene for resistance to ryegrass blast (Pyricularia sp.) in Italian ryegrass (Lolium multiflorum Lam.).

Ryegrass blast, also called gray leaf spot, is caused by the fungus Pyricularia sp. It is one of the most serious diseases of Italian ryegrass (Lolium multiflorum Lam.) in Japan. We analyzed segregation of resistance in an F(1) population from a cross between a resistant and a susceptible cultivar. The disease severity distribution in the F(1) population suggested that resistance was controlled by a major gene (Lm Pi1). Analysis of amplified fragment length polymorphisms with bulked segregant analysis identified several markers tightly linked to Lm Pi1. To identify other markers linked to Lm Pi1, we used expressed sequence tag-cleaved amplified polymorphic sequence (EST-CAPS) markers mapped in a reference population of Italian ryegrass. Of the 30 EST-CAPS markers screened, one marker, p 56, flanking the Lm Pi1 locus was found. The restriction pattern of p 56 amplification showed a unique fragment corresponding to the resistant allele at the Lm Pi1 locus. A linkage map constructed from the reference population showed that the Lm Pi1 locus was located in linkage group 5 of Italian ryegrass. Genotype results obtained from resistant and susceptible cultivars indicate that the p 56 marker is useful for introduction of the Lm Pi1 gene into susceptible germ plasm in order to develop ryegrass cultivars with enhanced resistance to ryegrass blast.