Resistance to Fusarium Wilt in Common Bean.

Fusarium wilt of dry bean (Phaseolus vulgaris L.), caused by Fusarium oxysporum Schl.:Fr. f. sp. phaseoli  Kendrick & Snyder (Fop), has become an important disease in the High Plains and western USA.  The disease causes rapid yellowing of foliage, defoliation and ultimately plant death and yield loss. Genetic resistance is needed to limit disease losses because cultural and chemical control measures are inadequate.  Resistance is strain specific and resistance genes can provide resistance to multiple strains of the pathogen. The objectives of this research were to determine the mode of resistance and tag the resistance genes using molecular markers.  We developed a recurrent inbred backcross population from the cultivar Sierra and experimental line Lef-2RB.  These lines were selected as parents because previous studies indicated Lef-2RB had a gene that conferred resistance to races 1, 4, and 5 Fop; while Sierra possessed resistance to only race 4 Fop. F₂ progeny and a recombinant inbred line population (RIL) were developed to determine the modes of inheritance and tag the resistance genes.  A single independent dominant gene for resistance occurs in each parent and are not allelic. Results support the conclusion that the Sierra gene provides resistance to race 4, while the Lef-2RB gene controls resistance to races 1, 4 and 5. Molecular markers were identified that are associated with these resistance genes.  These markers should facilitate selection for resistance to Fop races 1, 4 and 5 in common bean.