Sensitivity of Rhizoctonia solani isolates to fungicides and evaluation of peanut cultivars to Rhizoctonia limb rot1

Abstract

Abstract Twenty-one isolates were made from typical Rhizoctonia limb rot lesions of Florunner peanuts (Arachis hypogaea L.) and one each from a peanut pod and cowpea (Vigna unguiculata Walp.). Isolates of Rhizoctonia solani were characterized for sensitivity to three sterol-inhibiting fungicides, PCNB and chlorothalonil. Diniconazole, cyproconazole, and tebuconazole were the most effective inhibitors of radial growth, with a mean EC50 of 0.028, 0.056, and 0.166 μg/μL, respectively. EC50s for PCNB and chlorothalonil were 4.06 and 4.85 μg/mL, respectively. A technique to reproduce the disease in the greenhouse was developed and used to evaluate 18 peanut cultivars for resistance to limb inoculation with R. solani. NC 6, NC 7, New Mexico Valencia A, and Florunner were the most susceptible cultivars based on lesion length. Wounding before inoculation resulted in significantly increased lesion length for 15 of 18 cultivars. In a three-year (1986–88) field trial, NC 6, Florigiant, and NC 7 were the most susceptible cultivars, while VA 81B and Toalson appeared to be the most resistant.