Plantlet resistance of cucurbit cultivars to root rot caused by Phytophthora capsici

Abstract

The aim of this work was to evaluate the resistance of cucurbit cultivars at seedling stage to root rot caused by Phytophthora capsici. Sixty-three cucurbit cultivars, comprising Cucurbita moschata (17 cvs.), C. maxima (5 cvs.), C. pepo (10 cvs.), "morango" (Cucurbita spp., 3 cvs.), cucumber (Cucumis sativus, 13 cvs.), melon (Cucumis melo, 7 cvs.) and watermelon (Citrullus lanatus, 8 cvs.) were evaluated. The experiment was carried out in greenhouse, in a randomized block design with four replicates (8 plantlets/plot). Ten days after sowing, at the cotiledonar stage, the plantlets were inoculated by pouring 3 mL of inoculum (10⁴ zoospores/mL) at the plantlet base. Plants were rated for disease symptoms three days after inoculation using a 0-7 scale (0=no visible symptoms; 7=dead plant). By cluster analysis, cultivars with mean disease ratings 0.44 to 2.54 were considered as resistant (13 cvs.); 4.49 to 5.37 as intermediate; and 5.64 to 7.0 as susceptible. Twelve cucumber cultivars showed higher levels of resistance and were rated as resistant (0.44 to 0.54), and only one was considered as intermediate (cv. Shibata, grade=4.56). Most of the cucurbit cultivars tested were susceptible: watermelon (8 cultivars=7.0), melon (6 cvs., 5.97-7.0). Imperial (2.05) was resistant; the others, ranging from 5.98 to 7.0, and the Cucurbita group, ranging from 4.49 to 7.0, were susceptible.