Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/5/2004
Publication Date: 6/1/2004
Citation: Berland, P.A., Thies, J.A., Fery, R.L. 2004. Evaluation of cowpea germplasm for seedling resistance to Rhizoctonia solani [abstract]. Phytopathology. 94:S8.
Technical Abstract: Rhizoctonia solani is a major pathogen of cowpea (Vigna unguiculata) and causes substantial yield losses worldwide. Resistant cultivars would be the preferred control measure. A greenhouse method to evaluate cowpea germplasm for seedling resistance was developed using inoculum cultured on dent corn kernels. A total of 360 U.S. Plant Introductions (PI) from the core subset of the USDA Cowpea Germplasm Collection and a moderately resistant check, Kentucky Wonder-191 pole bean (Phaseolus vulgaris), were evaluated. Five seeds per PI were planted individually in 0.2-L cells containing pasteurized soil (2 sand : 1 soil) mixed with 0.5g of infested kernels chopped to a particle size of 0.6 x 0.6 x 0.2 cubic centimeters. Two weeks later, seedlings were rated for disease on a 1 to 5 scale with 1 = 0 to 3, 2 = 4 to 25, 3 = 26 to 50, 4 = 51 to 80, and 5 = 81 to 100% of hypocotyl circumference covered with lesions. Disease indices ranged from 2.4 to 5.0 with nine PI exhibiting moderate resistance (<3.0). Moderately resistant PI were re-evaluated in a replicated test using a randomized complete block design. Disease indices were lower in the moderately resistant PI (mean = 2.4) than in the susceptible PI (mean = 4.2) (P<0.0001).