When a range of genotypes of the genusPisumwas inoculated withAscochyta pisisome remained uninfected or symptomless whereas the reactions of others ranged from a hypersensitive resistance through various levels of susceptibility to almost lethal infection. This variation, categorized on a six‐class scale, was used to describe the reactions of 57 isolates ofA. pisicollected from pea crops widely distributed in Britain when inoculated on to 14 differential lines ofPisum.Five major pathotype groups were distinguished and a set of lines nominated as standard differential host
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