SCREENING FOR PARTIAL RESISTANCE TO AN ISOLATE OF CROWN RUST (PUCCINIA-CORONATA F-SP AVENAE) RACE-264 IN OAT CULTIVARS AND BREEDING LINES

Partial resistance to crown rust was assessed in 19 cultivars and 14 oat (Avena sativa) breeding lines. Plants were sown in two growing seasons (1989, 1990) in 3.8 x 1.0 m field plots with five rows in each plot. A hill of the line NZ-3 was planted in the centre of each plot and 10 oat plants of this hill were inoculated with a urediniospore suspension of isolate CR13 of Puccinia coronata f. sp. avenae race 264. Crown rust severity was visually estimated as percent leaf area diseased at weekly intervals, commencing at approximately Zadoks growth stage 37, on the flag leaf and on the four preceding leaves on each of four randomly selected plants per plot. The parameters used in the data analysis were the cumulative proportion of leaf area diseased (CPLAD), averaged for all five leaves sampled, and the proportion of flag leaf area diseased (PFLAD). The CPLAD and PFLAD values were submitted to both principal component and cluster analysis to obtain specific groups of oat cultivars and breeding lines with similar levels of partial resistance to isolate CR13. The results obtained from the cluster analysis of the CPLAD values gave a group of six oat lines that displayed high levels of partial resistance in both years; OA 712-17 Woodstock, Fidler, Sylva, Ultima, and Glen. The cluster analysis of the PFLAD grouped five and eight oat accessions displaying high levels of partial resistance in 1989 and 1990, respectively. The oat accessions common in cluster groupings of both years based on PFLAD were similar to those obtained based on the CPLAD parameter, indicating that the former could be used in mass screening for partial resistance to crown rust.