Inheritance of Resistance to Phytophthora Root Rot in Chili Pepper Depending on Inoculum Density and Parental Genotypes

Phytophthora capsici Leonian causes root rot and stem blight in pepper (Capsicum spp.) and is a serious threat to pepper production because of its ability to infect every root, stem, and leaf at any developmental stage. Recently, pepper F1 cultivars resistant to Phytophthora root rot have been commercially released in Korea. However, despite many studies, the inheritance of resistance remains controversial due to differences in experimental methods, including pepper materials, pathogen isolates, inoculation conditions, and evaluation methods. Our aim was to determine the inheritance of Phytophthora root rot resistance by using three different F2 populations derived from crosses between ‘CM334’ (a resistant male parent) and three Korean landraces, ‘Subicho’ ‘Daehwacho’ and ‘Chilsungcho’ (susceptible female parents), and inoculating them with three
different pathogen densities (1x10^4, 1x10^5, and 1x10^6 zoospores/ml). The distribution patterns were varied, depending upon female parental susceptibility as well as inoculum densities. For example, as the inoculum density increased, pepper survival rates decreased. In all of the inheritance analyses, one common dominant resistant gene was participated in resistance to Phytophthora root rot. In addition, we found that a complementary gene, together with the major dominant gene, was necessary for resistance at a high (106) inoculum density, based on a 9:7 (R:S) segregation ratio. This study will be helpful in developing
molecular markers linked to genes that are resistant to Phytophthora root rot.