Coincident QTL which determine seedling and adult plant resistance to stripe rust in barley

Barley stripe rust (caused by Puccinia striiformis Westend. f. sp. hordei) is an important disease of barley (Hordeum vulgare L. subsp. vulgare). This disease reached the Americas in 1975. It is now endemic from the Andean region of South America to western North America. We are systematically, mapping quantitative resistance genes present in ICARDA/CIMMYT germplasm and introgressing these genes into barley germplasm adapted to western North America. Resistance to stripe rust in the Triticeae can he race- and growth-stage specific. In this study, we mapped genes conferring resistance at the seedling stage, after inoculation with defined isolates (PSII-I, PSH-13, PSH-14), in a doubled haploid population in which adult plant resistance genes had previously been mapped. The disease reaction data for each of three isolates fit a 3:1 (susceptible: resistant) ratio, indicating that two genes are required for resistance. Quantitative trait loci (QTL) effects and significance were estimated by means of QTL mapping procedures and logistic regression analysis, taking into account the binomial distribution of the trait. Two resistance QTL ne on chromosome 5 (511) and one on chromosome 6 (6H)-were detected and in all cases 'Shyri' contributed the resistance alleles. No QTL X race interaction was detected. The two seedling resistance QTL map to the same regions of the genome as two of the four adult plant resistance QTL. These data Jay the foundation for more detailed analyses directed at unraveling the genetics of qualitative and quantitative disease resistance mechanisms.