Susceptibility of Selected Cultivars of Forage Grasses to Magnaporthe oryzae Isolates from Annual Ryegrass and Relatedness of the Pathogen to Strains from Other Grasses

Isolates of Magnaporthe oryzae obtained from annual ryegrass were inoculated onto two or three cultivars each of seedlings and adult plants of annual ryegrass, perennial ryegrass, tall fescue, meadow fescue, and festulolium. All plant species tested were very susceptible as seedlings, although modest differences in susceptibility among cultivars were sometimes observed. Adult plants of all species tested exhibited blighting as well, suggesting that all could allow inoculum buildup in pastures where they are sown. DNA fingerprinting tests indicate that the M. oryzae isolates causing disease on annual ryegrass appear to be from the same pathogen population responsible for the gray leaf spot epidemics on perennial ryegrass. This disease appears to pose a significant threat to the use of annual ryegrass sown in late summer on Kentucky dairy and beef farms.