Quantitative resistance and its components in 16 barley cultivars to yellow rust, Puccinia striiformis f. sp. hordei

Abstract

Sixteen barley cultivars with a suscep- tible infection type (IT = 7-8) in the seedling stage to an isolate of race 24 of Puccinia striiformis f. sp. hordei were planted at two locations in Mexico. Disease severity (DS) parameters were assessed for the flag leaf and for the upper three leaves. The cultivars represented at least five levels of quanti- tative resistance ranging from very susceptible to quite resistant. ''Granado'', ''Gloria/Copal'' and ''Calicuchima-92'' represented the most resistant group and had an IT of 7 or 8. The culti- var · environment interaction variance, although significant, was very small compared with the cultivar variance. The disease severity parameters were highly correlated. The monocyclic parameter DSm, measured when the most susceptible cultivar had reached its maximum DS, was very highly correlated with the area under the disease progress curve (AUDPC), r being 0.98. Components of quantitative resistance were evaluated in two plant stages. In the seedling stage small cultivar effects for the latency period were observed, which were not correlated with the quantitative resistance measured in the field. In the adult plant stage the latency period (LP), infection frequency (IF) and colonization rate (CR) were measured in the upper two leaves. The LP was much longer than in the seedling stage and differed strongly between cultivars. The differences in IF were too large, those in CR varied much less. The components showed association with one another. The LP and IF were well correlated with the AU- DPC (r = 0.7-0.8).