RESISTANCE TO OAT CROWN RUST IN DIPLOID AND HEXAPLOID AVENA

The minimum number of Pc genes for resistance to oat crown rust (Puccinia coronata var. avenae) was determined from infection-type data based on the interactions of several oat lines and 47 isolates of crown rust from the Iowa State University collection. Infection-type data from seedlings of seven diploid oat accessions, a hexaploid chromosome addition line (X117), and its recurrent parent (C649), were evaluated in reference to 33 differentials to determine low or high infection type. At least 17 unique crown rust resistance genes can be detected in the hexaploid differentials with the Iowa State University crown rust collection. Four additional resistance genes can be detected among the diploid accessions. Among the diploid oat accessions, CI 2630, CI 3815, and CI 6954 (all Avena strigosa) were resistant to most isolates of crown rust, while CI 1994 (A. wiestii), CI 9009 (A. nuda), CI 3214 (A. wiestii), and CI 4748 (A. strigosa) were susceptible to most isolates. An evaluation of parents from two diploid mapping populations revealed 37 differential reactions that can be detected and mapped in the progeny from a cross between CI 2630 and CI 9009, and 40 from a cross between CI 3815 and CI 1994. The two crosses have 32 differential reactions in common.