The evidence for abundance of QTLs for partial resistance to Puccinia hordei on the barley genome

Using AFLP markers, a linkage map was constructed based on a recombinant in bred population of barley derived from a cross between a leaf rust suscepti ble line, L94, and a partially resistant line, 116-5. The constructed map s howed a similar marker distribution pattern as the L94 x Vada map. However, it contained more large gaps, and for some chromosome regions no markers w ere identified. These regions are most likely derived from L94 because 116- 5 was selected from the progeny of a cross of L94 x cv. Cebada Capa. Five Q TLs for partial resistance to isolate 1.2.1. were mapped on the L94 x 116-5 map. Three QTLs were effective in the seedling stage, jointly contributing 42% to the total phenotypic variance. Three QTLs were effective in the adu lt plant stage, collectively explaining 35% of the phenotypic variance. Evi dence for two additional linked minor-effect QTLs effective in the adult pl ant stage was also uncovered. The major-effect QTL, Rphq3, was the only one that was effective in both developmental stages. Moreover, Rphq3, was also identified in the L94 x Vada population, being effective to two rust isola tes. The other QTLs were detected in either of the two populations, providi ng evidence for the existence of many loci for partial resistance to leaf r ust on the barley genome. To date, 13 QTLs for partial resistance have been mapped, therefore, a strategy of accumulating many resistance genes in a s ingle cultivar, resulting in a high level of partial resistance, is feasibl e.