Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2003
Publication Date: 8/1/2003
Citation: Berland, P.A., Thies, J.A., Fery, R.L. 2003. Methodology for evaluating cowpea germplasm for resistance to Rhizoctonia solani [abstract]. Hortscience. 38(6):1297.
Technical Abstract: Rhizoctonia solani is an important pathogen of cowpea (Vigna unguiculata) worldwide and is the predominant cause of seedling mortality. Identification of resistant cultivars could provide farmers with a method to reduce crop losses due to this pathogen. We evaluated methodologies for screening cowpea germplasm for reaction to R. solani. Cowpea cultivars utilized were White Acre, Charleston Greenpack, California Blackeye no. 5, Mississippi Silver, Black Crowder, Mississippi Cream, Texas Cream-40, Colossus-80, Floricream, and Pinkeye Purple Hull. Inoculum was produced by inoculating autoclaved dent corn kernels with R. solani. Seedlings were rated for disease on a 1 to 5 scale with 1 = 0 to 3%, 3 = 26 to 50%, and 5 = 81 to 100% hypocotyl decay. Three inoculation methods were evaluated. Seedling emergence: At planting, one infected corn kernel was placed 1 cm below each cowpea seed and seedlings were rated for disease two weeks later. All cultivars exhibited poor emergence. Stem inoculation: Each seedling was inoculated at the cotyledon stage by placing one infected kernel next to the hypocotyl 1 cm below the soil surface and rated for disease two weeks later. These tests were conducted at 24 degrees C, 27 degrees C and 32.5 degrees C and the most severe disease occurred at 24 degrees C. Chopped kernel inoculation: Infected corn was chopped in a blender to produce three sizes of inoculum and mixed with pasteurized soil at four concentrations. Seeds were planted in 0.2-L cells containing each soil-inoculum treatment and seedlings were evaluated two weeks later. The largest inoculum size x highest inoculum concentration resulted in the most severe disease across all cultivars.