Evaluation of Phytophthora root rot- and bacterial wilt-resistant inbred lines and their crosses for use as rootstocks in pepper (Capsicum annuum L.)

Breeding lines and their crosses with genic male sterile (GMS) and cytoplasmic male sterile (CMS) lines, developed for use as rootstocks with resistance to Phytophthora root rot and bacterial wilt, were evaluated for their resistance against these diseases and for supporting the growth of scions. Five inbred lines of the Yanggang (YG) series of breeding lines and 10 crosses between these lines and the male sterile lines, the commercial rootstock Tantan, and the susceptible scion cultivar Gilsang were tested for resistance to infection by Ralstonia solanacearum and Phytophthora capsici at the seedling stage. YG4, YG5, GMS x YG5, and CMS x YG3 remained disease-free, whereas Gilsang succumbed to both diseases. The grafted plants, corresponding not-grated rootstocks, auto-grafted (Gilsang/Gilsang) and non-grafted Gilsang seedlings (controls) were inoculated with R. solanacearum, planted side-by-side in a greenhouse, and evaluated for incidence of bacterial wilt under hot greenhouse conditions during summer. Gilsang scions grafted to the rootstocks YG2, YG3, YG4, YG5, GMS x YG5, and CMS x YG6 remained healthy through the end of the experiment, without any symptoms of bacterial wilt, whereas Gilsang scions grafted to rootstocks CMS x YG2 and Tantan, as well as the auto-grafted and non-grafted Gilsang seedlings failed to survive the disease, with 100% death observed. The survival rate of the rootstocks to bacterial wilt was higher than that of the grafted plants, except for Tantan, in which all plants died. Thus, the resistant rootstocks developed and selected in this study were effective in the control of bacterial wilt under high temperature conditions. The rootstocks were found to have a minimal effect on the growth and fruit size of the scion.