Virulence of crown rust isolates (Puccinia coronata f.sp lolii) on genotypes of Italian and perennial ryegrass (Lolium multiflorum and L-perenne)

摘要

Crown rust samples were collected in 2004 on rust infected Italian and perennial ryegrass leaves at 28 sites in 11 European countries. Out of these 28 rust collections, 112 single-pustule isolates were produced to determine virulence frequency and complexity on 32 ryegrass genotypes. A high level of virulence diversity was observed within and between individual sampling sites. In total, 107 pathotypes with different virulence combination were found. Of these, just five combinations occurred twice. All 32 individuals were susceptible to at least two single-pustule isolates using a detached-leaf segment test. In the field, the 32 genotypes differed greatly in their susceptibility to crown rust. Nevertheless, the correlation between mean susceptibility in the field and virulence frequency of the 32 differentials was significant. The three most resistant genotypes in the field were also the genotypes with the lowest virulence frequency. Genetic analysis of resistance to crown rust in three genotypes of perennial ryegrass led to the identification of three dominant resistance genes: Pclol1, Pclol2 and Pclol3. Each of the three genes conferred resistance to a limited number of single-pustule isolates and was ineffective against at least one single-pustule isolate. The patterns of resistance reaction to specific single-pustule isolates provide evidence that the three R-genes represent distinct crown rust resistance genes in ryegrass. Moreover, the data demonstrate clearly the existence of pathotype specificity in crown rust of Lolium species.