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

Abstract

The genus Capsicum has been distinguished by its lack of compatible rootstocks with commercial cultivars to successfully protect against Phytophthora capsici. Criollo de Morelos 334 (CM334) has been used worldwide in crosses and as a rootstock to protect against P. capsici. However, novel sources of resistance to this pathogen, 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 provide a benefit to the grafted cultivar. Our objectives were 1) to evaluate grafting survival using ‘Pasilla 18M’ and CM334 as rootstocks of two susceptible commercial cultivars: Sweet Pepper California Wonder (CW) and Serrano Coloso; and 2) to evaluate 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 during 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 ungrafted 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% incidence. In contrast, intervarietal grafts remained almost free of infection (severity 0.14; incidence 0% to 4%). CM334 and ‘Pasilla 18M’ rootstocks are highly compatible with ‘Serrano Coloso’ and ‘Sweet Pepper CW’. ‘Pasilla 18M’ confers the same level of protection against P. capsici as CM334.