GENES FOR RESISTANCE IN BARLEY TO FINNISH ISOLATES OF RHYNCHOSPORIUM-SECALIS

Twenty Finnish isolates of Rhynchosporium secalis (Oud.) J.J. Davis, t he causal agent of scald, were taken from infected barley (Hordeum vul gare L.) plants and inoculated on to seedlings of a differential serie s of barley containing a range of major genes for resistance to the fu ngus, as well as on to six Nordic B-row spring barleys and three winte r ryes (Secale cereale L.). These fungal isolates derived from four si tes and three host varieties. Disease development was monitored on two leaves of seedlings in the greenhouse employing a standard scale, and on adult plants in the field by assessing the diseased area on the th ree uppermost leaves. A comparison was also made between the pathogeni city and virulence of ten Finnish and ten Canadian R. secalis isolates . The Finnish isolates varied in virulence, but with the exception of Algerian (CI 1179) seedlings and adult La Mesita (CI 7565) all seedlin gs and adult plants of the entire differential series were resistant t o all isolates. Canadian isolates were, on average, less virulent than Finnish isolates. All the Nordic checks were susceptible to all Finni sh and seven Canadian isolates, but differences in the degree of susce ptibility were evident. Isolates of R. secalis from barley were non-pa thogenic on rye, isolates from Elymus repens L. were non-pathogenic on barley and rye, and isolates from rye were only pathogenic on rye. Fi nnish R. secalis isolates contain no redundant pathogenic diversity. T he differential series represents a useful, but as yet untapped, sourc e of resistance to R. secalis for Finnish barley breeders.