No abstract

No abstract

Ascochyta blight, caused by Ascochyta fabae Speg., is a disease of faba bean (Vicia faba L.) of worldwide distribution. In this study we have conducted an experiment on Ascochyta fabae resistance in 165 recombinant inbred lines (RILs) developed by single-seed descent from the cross between resistant and susceptible lines (Vf6 × Vf136) in which A. fabae resistance QTLs (quantitative trait loci) have been previously reported in the original F2 population. Recombinant inbred lines were inoculated under controlled growth chamber conditions and evaluated for disease severity and infection type index. The linkage map was constructed by MAPMAKER V2.0 and the QTL analysis was carried out using QTL Cartographer. Two hundred and seventy-seven markers (238 RAPDs, 4 isozymes, 5 ESTs, 1 SCAR, 6 SSRs, 2 STSs, and 21 intron-spanning markers) mapped into 21 linkage groups covering 2.856.7 cM, with a mean inter-marker distance of 12.72 cM. Composite interval mapping identified two zones of putative QTL action in the RIL population for DSL (disease severity on leaves) and DSS (disease severity on stems) traits. Putative QTLs (Af1 and Af2) were identified on chromosome 3 and chromosome 2, respectively, and jointly explained 24% of the phenotypic variance of DSL and 16% of DSS. With this study we have (1) confirmed the QTLs for ascochyta blight resistance found in F3 families in the derived RILs (F6), (2) re-estimated their position and genetic effects, and (3) assessed the stability of these QTLs in different genetic backgrounds by comparison of the mapping data with a previous QTL study.

Ascochyta blight is an important disease of faba bean (Vicia faba L.). Yield losses can be as high as 90% and losses of 35–40% are common. The line 29H is one of the most resistant accessions to the pathogen (Ascochyta fabae Speg.) ever described. In this work, we aimed to validate across generations the main quantitative trait loci (QTLs) for ascochyta blight resistance identified in the cross 29H × Vf136 and to test their stability under field conditions. QTLs located on chromosomes II and III have been consistently identified in the recombinant inbred line (RIL) population of this cross, in both controlled (growth chamber) and field conditions and, thus they are good targets for breeding. In addition, a new QTL for disease severity on pods has been located on chromosome VI, but in this case, further validation is still required. A synteny-based approach was used to compare our results with previous QTL works dealing with this pathogen. Our results suggest that the QTL located on chromosome II, named Af2, is the same one reported by other researchers, although it is likely that the donors of resistance differ in the allele conferring the resistance. By contrast, the location of Af3 on chromosome III does not overlap with the position of Af1 reported by other authors, suggesting that Af3 may be an additional source of resistance to ascochyta blight.