Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

Abstract This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianaene-crosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant(CM334) cultivars of pepper (Capsicum annuumL.). Populations, composed of Pr, Ps, F 1 ,F 2 ,BC 1 Pr, and BC 1 Ps gen-erations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an addi-tive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 ,Pn Ko2 and Pn Kr1 , which showed lowaggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 ,Pn Bz2 and Pn Kr2 , epistasis was an integralcomponent of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianaewas dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates wasefficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was morestable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases,the additive variance was significant and greater than the environmental and dominance variance.