Survival of Intervarietal Grafts of Sweet and Serrano Peppers (Capsicum annuum L.) on Pasilla 18M as a New Rootstock Against Phytophthora capsici Leo

The genus Capsicum has been distinguished by its lack of compatible root-stocks with commercial cultivars to successfully protect against Phytophthora capsici. Criollo de Morelos 334 (CM334) has been used worldwide in crosses and as a root-stock to protect against P. capsici. However, novel sources of resistance to this patho-gen, such as 'Pasilla 18M' have not yet been explored as rootstocks. A good rootstock should be highly compatible with the scion and also maintain the quality and/or pro-vide a benefit to the grafted cultivar. Our objectives were 1) to evaluate grafting sur-vival using 'Pasilla 18M' and CM334 as rootstocks of two susceptible commercial cultivars: Sweet Pepper California Wonder (CW) and Serrano Coloso; and 2) to eval-uate the efficiency of 'Pasilla 18M' as rootstock against P. capsici using CM334 as a resistant control. Grafting survival was analyzed over 58 days after grafting in sets of 60 plants per varietal combination. Disease severity and incidence were recorded dur-ing 24 days after inoculation with P. capsici (DAI). Incidence was also evaluated at 54 and 84 DAI. A severity scale from 0 (healthy plant) to 4 (dead plant) was applied to evaluate root rot per plant. Incidence was recorded as the percent of diseased plants (severity >0). Grafting survival of intervarietal grafts was 87% to 94%, similar to un-grafted cultivars, and exceeding autograft survival. Ungrafted and autografted Sweet Pepper and Serrano showed root rot severities 2.3 to 3.3, with 89% to 100% inci-dence. In contrast, intervarietal grafts remained almost free of infection (severity 0.14; incidence 0% to 4%). CM334 and 'Pasilla 18M' rootstocks are highly compati-ble with 'Serrano Coloso' and 'Sweet Pepper CW'. 'Pasilla 18M' confers the same level of protection against P. capsici as CM334.