Rust diseases of ryegrass

In Switzerland the most common rust disease of Italian and perennial ryegrass is crown rust (Puccinia coronata f.sp. lolii). The alternate host of P. coronata is common buckthorn (Rhamnus cathartica). Breeding for resistance to crown rust is a major component of our ryegrass improvement program. In order to assess the variation in pathogenicity of crown rust and the degree of host resistance to them, a range of Italian, hybrid and perennial ryegrass cultivars was tested for their reaction to Swiss crown rust collections. Among cultivars, significant differences in susceptibility were observed. Most Swiss cultivars showed a low infection level. For sixteen cultivars significant differences in infection level between rust collections occurred. Based on these results, three distinct groups of crown rust collections were identified. The host species, on which the urediospores were collected, had an important influence on the infection type of the different cultivars.