Genetic Analysis of Phytophthora Root Rot Race-specific Resistance in Chile Pepper

Abstract

Phytophthora capsici Leon., causal agent of phytophthora root rot, is one of the most devastating pathogens attacking chile pepper (Capsicum annuum L.) plants. Many studies have tried to better understand phytophthora resistance, but the genetic behavior is not completely understood. To determine if phytophthora root rot resistance in chile pepper is controlled by multiple alleles at a few loci, or multiple genes at different loci, five recombinant inbred lines (RILs) were evaluated. The resistant accession, Criollo de Morelos-334, and the susceptible cultivar, Early Jalapeno, were hybridized to develop multiple RILs. After seven generations of selfing using the single seed descent method, four RILs were selected based on their phenotypic response to inoculation by five P. capsici isolates. The RILs were hybridized to each other to obtain F1 and F2 populations. The F2 populations were inoculated with single and a pair of races of P. capsici. When the F2 populations were inoculated with a single race, ratios of three resistant:one susceptible were obtained in the majority of the populations, indicating the action of an independent single gene. When the F2 populations were inoculated with a combination of two races, segregation ratios of 15 resistant:one susceptible were observed in two populations out of the four populations. The presence of susceptible individuals in all of the F2 population indicates that the resistant genes for the different P. capsici races are located at different loci. However, the rejection of the segregation ratio in one of the F2 population under a single race inoculation and in two of the F2 populations challenged with a combination of two races suggest a linkage phenomenon between some of the R genes. None of the RILs evaluated in this study displayed allelism for phytophthora root rot resistance.