Identification and confirmation of quantitative trait loci for root rot resistance in snap bean

Root rot, caused by several pathogens including Pythium ultimum Trow and Aphanomyces euteiches Drechs f. sp. phaseoli W.F. Pfender and D.J. Hagedorn, is an important disease complex of snap bean (Phaseolus vulgaris L.). The objectives of this study were to identify, map, and validate markers associated with root rot resistance in three snap bean populations. An 'Eagle' x 'Puebla 152' recombinant inbred line (RIL) population was evaluated for root rot by plant stand percentage, plant vigor, and plant biomass. Field data were combined with a random amplified polymorphic DNA (RAPD) map to identify quantitative trait loci (QTL) associated with resistance using composite interval mapping. In addition, two inbred backcross (IBC) populations (EEP and EPH) derived from a cross (Eagle x Puebla 152) to Eagle and 'Hystyle' respectively were evaluated. Five regions from linkage groups B6, B3, and B7 of the P. vulgaris core map were associated with QTL for root rot resistance. High levels of resistance were also observed in several lines of the IBC populations. A major QTL for root rot resistance was associated with the tightly linked AD9.950 and S18.1500 RAPD marker alleles from linkage group B6 in the RIL population and confirmed explaining 25 to 49% of the variability for plant vigor and biomass in the IBC populations. The exploitation of the linkage disequilibrium between the AD9.950 and S18.1500 RAPD markers derived from Puebla 152 and Eagle can facilitate the development of root rot resistant cultivars.