A Rapid Method for Evaluating Citrus Seedlings for Resistance to Foot Rot Caused by Phytophthora citrophthora. U. Afek, Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Faculty of Agriculture, P. O. Box 12, Rehovot 76100, Israel. A. Sztejnberg, and Z. Solel. Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Faculty of Agriculture, P. O. Box 12, Rehovot 76100, Israel; and Department of Plant Pathology, Volcani Center, ARO, Bet Dagan 50250, Israel. Plant Dis. 74:66-68. Accepted for publication 31 July 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0066.

A method was developed to evaluate the resistance of citrus rootstocks to foot rot disease caused by the fungus Phytophthora citrophthora. This method involved inoculating three-month-old branches of seedling rootstocks with an isolate of P. citrophthora and measuring the length of lesions that developed four days later. The degree of resistance was determined by comparing the lengths of lesions on seedlings of species of unknown resistance to lengths on seedlings of rootstock species with known resistance. The lengths on seedlings of resistant species were 2.8 mm for Citrus macrophylla and 3.2 mm for Poncirus trifoliata; lengths on moderately-resistant species were 5.0 mm for C. aurantium and 5.2 mm for P. trifoliata × C. sinensis; lengths on susceptible species were 11.0 mm for both C. jambhiri and C. sinensis. Thirty-two hybrids (P. trifoliata × ‘poorman orange’) were tested using this method. Of these, 14 hybrids were resistant, eight were moderately resistant, and 10 were susceptible.