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 topepper production because of its ability to infect every root, stem, and leaf at any developmental stage. Recently, pepper F₁cultivars resistant to Phytophthora root rot have been commercially released in Korea. However, despite many studies, theinheritance of resistance remains controversial due to differences in experimental methods, including pepper materials, pathogenisolates, inoculation conditions, and evaluation methods. Our aim was to determine the inheritance of Phytophthora root rotresistance by using three different F₂ populations derived from crosses between ‘CM334’ (a resistant male parent) and threeKorean landraces, ‘Subicho’ ‘Daehwacho’ and ‘Chilsungcho’ (susceptible female parents), and inoculating them with threedifferent pathogen densities (1×104, 1×105, and 1×106 zoospores/ml). The distribution patterns were varied, dependingupon female parental susceptibility as well as inoculum densities. For example, as the inoculum density increased, pepper survivalrates decreased. In all of the inheritance analyses, one common dominant resistant gene was participated in resistance toPhytophthora root rot. In addition, we found that a complementary gene, together with the major dominant gene, was necessaryfor resistance at a high (106) inoculum density, based on a 9:7 (R:S) segregation ratio. This study will be helpful in developingmolecular markers linked to genes that are resistant to Phytophthora root rot.