Pathogen variability and host resistance in bacterial pustule disease of cowpea in Africa
AbstractCowpea lines tested with suspensions of the bacterial pustule pathogen (Xanthomonas sp.), using the infiltration inoculation method, showed three types of reaction - brown hypersensitive resistant (BRH), resistant (R) and susceptible (S). Ten isolates, inoculated in four cowpea lines representing BHR, R and S reactions, could be classified into three distinct pathogenic races by the ability of an isolate to overcome the BHR reaction in one or two lines. The R reaction was table against all the three races. Race 1 may be widely prevalent in West Africa and races 2 and 3 in East Africa. A set of cowpea cvs with differential reactions to identify these races is proposed. In the screening of 234 cowpea lines, 166 reacted uniformly BHR to race 1 and S to races 2 and 3, 23 were BHR to races 1 and 2 but S to race 3, and 11 were R to all three races. The advantages of infiltration over the spray method of inoculation for screening cowpea lines against bacterial pustule are discussed.