Genetics of resistance to Puccinia coronata f sp avenae in two Avena sativa accessions

The inheritance of resistance to oat crown rust [Puccinia coronata f. sp. avenae] was studied in two heterogeneous resistant accessions, MG 85039 and MG 85181, identified in preliminary screening of 45 oat (Avena sativa) accessions obtained from the National Research Council Germplasm Institute, Italy. A single resistant plant, selected from each of the accessions, was crossed to the susceptible cultivar Makuru. Segregation of F-3 families of the Makuru/MG 85039 cross for resistance to crown rust indicated that this accession had two independent genes for resistance, designated PcA and PcB. Segregation for resistance of F-3 families of the Makuru/MG 85181 cross indicated that this accession had a single gene, designated PcC. Genes PcA, PcB, and PcC conditioned, respectively, resistance to 19, 4, and 10 of 22 crown rust isolates in seedling tests. Gene PcA appears to be the most useful source of resistance to crown rust in the Canadian prairie region. It conditioned a high level of resistance to over 97% of all iso lates obtained from the annual crown rust surveys in Manitoba from 1991 to 1994. It is linked to gene Pc35 and is independent of genes Pc38, Pc39, Pc45, Pc48, Pc55, Pc62, Pc63, Pc64, and Pc68. In comparison with the known Pc genes, there is ample evidence that PcA is a gene not previously described; it was assigned the gene symbol Pc96. This gene should be a valuable source of resistance for the diversification of resistance gene combinations used in the development of new oat cultivars.