Specialization of crown rust (Puccinia coronata Corda) on clones of Italian ryegrass (Lolium multiflorum Lam.)

Summary Cultures of crown rust (Puccinia coronata Corda) from a mixed uredospore population obtained from plants in 16 localities in England and Wales were multiplied on four of 10 initially resistant clones of Italian ryegrass (Lolium multiflorum Lam.). Only two of the four cultures were found to be most pathogenic on the clones on which they had been multiplied. One clone became very susceptible to its own culture but the other became only moderately susceptible. Clone/culture interactions occurred which were not obviously related to the clone of origin of the culture. Thus, there was considerable genetic diversity in the crop which would tend to limit the multiplication of new races. There was a strong correlation between visual score for susceptiblity and uredospore production, showing the value of visual scores for resistance breeding.