Locating genes associated with Ascochyta fabae resistance in Vicia faba

Abstract

Ascochyta blight, caused by Ascochyta fabae Speg.,is a disease of faba bean (Vicia faba L.) of world-wide distribution. Although sources of resistance have been identified, little is known about its genetic basis and gene location. Molecular analyses were carried out using plant tissue from 196 individual F₂ plants derived from a cross between susceptible and resistant lines. F₂-derived F₃ 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 quantitative trait loci (QTL) analysis was carried out using QTL Cartographer. One hundred and twenty-one out of 130 marker loci could be mapped into 16 linkage groups. Nine linkage groups were assigned to specific chromosomes analysing common markers with previous studies that used primary trisomics to establish the chromosomal location of markers/genes. By simple interval mapping (SIM), 2 zones of putative QTL action were detected. Using forward-backward stepwise regression, 4 markers were selected to be used as cofactors in composite interval mapping (CIM). Putative QTLs (Af1 and Af2) were identified on linkage groups VIII (chromosome 3) and IVa (chromosome 2), respectively, and jointly contributed about 46% of the total phenotypic variance. Af1 displayed pure additive gene action and Af2 showed considerable dominant effect.