Resistance to stripe rust in durum wheats, A-genome diploids, and their amphiploids

Stripe rust (caused by Puccinia striiformis Westend.) is a wheat disease of worldwide importance. Seedlings of 75 accessions of Triticum boeoticum, 12 of T. monococcum, 16 of T. urartu, 230 of durum wheat (T. turgidum L. var. durum), and 128 amphiploids (genome AAAABB) involving the crosses of the three diploid species (AA) with T. turgidum (AABB) were evaluated in the greenhouse for their reaction to P. striiformis race 14E14. Durum wheats and the amphiploids were also evaluated at two field locations in Mexico with the same race for their adult plant response. Resistant seedling reactions (infection types: 0-3 on a 0-9 scale) were seen for 10 (13%) accessions of T. boeticum, 19 (8%) accessions of T. turgidum and 32 (25%) amphiploids. The remaining accessions were either moderately resistant (ITs 4-6) or susceptible (ITs 7-9). The three amphiploids derived from the crosses of seedling resistant I boeoticum and T. turgidum, were resistant as seedlings. Among the 51 amphiploids involving one resistant parent, 29 were resistant and the remaining 22 displayed intermediate to susceptible reactions. Suppressors for resistance were common in the A and AB genomes and suppression was resistance gene specific. Forty-five (20%) durums showed adequate field resistance (relative AUDPC < 10% of the susceptible check 'Morocco'). These included the 19 seedling resistant durums. Presence of genes involved in adult plant resistance was evident, because 26 of the remaining adult plant resistant durums had displayed intermediate-susceptible seedling reactions. Though the seedling reactions of the amphiploids varied from low to high, all involving the adult plant resistant durums possessed adequate field resistance. The resistant, newly produced, AAAABB amphiploids are useful genetic resources for stripe rust resistance which could be transferred to the cultivated T. turgidum.