Locating quantitative trait loci associated with Orobanche crenata resistance in pea

Orobanche crenata (broomrape) is a root parasite that represents the major constraint for pea (Pisum sativum) cultivation in the Mediterranean area and the Middle East. The efficacy of available control methods is minimal and breeding for O. crenata resistance is considered the most promising strategy of control. Only moderate levels of incomplete resistance are available in pea germplasm. In order to identify and map the quantitative trait loci (QTL) controlling the trait, 115 F₂ plants derived from the cross between a susceptible and a resistant parent were analysed using isozymes, random amplified polymorphic DNA and sequence tagged site markers. F₂-derived F₃ lines were studied for O. crenata resistance under field conditions. The linkage map was constructed with MAPMAKER V2.0. Of 217 markers, 120 could be mapped into 21 linkage groups. Linkage groups consisted of 13 to two marker loci covering 1770 cM. The mean inter-marker distance was 17.64 cM. Simple interval mapping (SIM) and composite interval mapping (CIM) were performed using QTL Cartographer. The CIM approach using five cofactors was clearly the most efficient way to locate putative QTL. Two QTL for O. crenata resistance (Ocp1 and Ocp2), explaining only a moderate portion of the observed variation (9.6% and 11.4% respectively), were detected.