Inheritance of Resistance to Two Races of Fusarium Wilt in Three Cowpea Cultivars1

Fusarium wilt [caused by Fusarium oxysporum f. sp. tracheiphilum (E.F. Sm.) Snyder and Hansen] is a serious disease of cowpea [Vigna unguiculata (L.) Walp.] in California. The objectives of this study were to determine the inheritance of resistance to F. oxysporum f. sp. tracheiphilum races 2 and 3 in ‘California Blackeye Number Five’ (CB5), ‘California Blackeye Number Three’ (CB3), and line 7964, and to determine if the genes for resistance to each race were independent of each other. Cultivar CB5 is susceptible and CB3 and 7964 are resistant to races 2 and 3. The F1, BC1, F2, F3, and F5 progenies were evaluated for resistance to each race using a seedling root dip inoculation procedure. Some F1 and F2 progenies were also evaluated for resistance using a tray inoculation procedure. A single dominant race 3 resistance gene was identified in CB3 and a single dominant race 2 resistance gene was identified in 7964. The F3 family reaction to both races suggested that the race 3 gene in CB3 also conferred incompletely dominant resistance to race 2, and the race 2 gene in 7964 also conferred incompletely dominant resistance to race 3. The reaction of F5 lines to both races did not support this hypothesis. It was concluded that CB3 also possessed a single incompletely dominant gene for race 2 resistance and that 7964 also possessed a single incompletely dominant gene for race 3 resistance.