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United States Department of Agriculture

Agricultural Research Service

Title: Methods for Evaluating Cowpea Germplasm for Seedling Resistance to Rhizoctonia Solani

Authors
item Berland, Paul
item Thies, Judy
item Fery, Richard

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2003
Publication Date: August 9, 2003
Citation: Berland, P.A., Thies, J.A., Fery, R.L. 2003. Methods for evaluating cowpea germplasm for seedling resistance to Rhizoctonia solani [abstract]. Phytopathology. 93:S8. Publication No. P-2003-0605-AMA.

Technical Abstract: Rhizoctonia solani is an important pathogen of cowpea (Vigna unguiculata) worldwide and is the predominant cause of seedling damping-off. The ideal control measure would be the utilization of resistant cultivars. Single seeds of Charleston Greenpack and White Acre cowpea and Kentucky Wonder-191 pole bean (Phaseolus vulgaris) were planted in 0.2-L cells containing pasteurized soil (2 sand : 1 soil) infested with one of 12 inoculum treatments. Inoculum cultured on dent corn kernels and chopped to three sizes (0.4 x 0.4 sq. cm, 0.6 x 0.6 sq. cm, and 0.8 x 0.8 sq. cm) was used at four rates (0.33, 0.67, 1.33, and 2.67 g per cell) to inoculate single-seed cells. Seedlings were rated for disease two weeks later 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. Generally, disease severity was greater in treatments with larger particle size x higher inoculum rates (probability less than 0.0001). Average disease ratings for White Acre, Charleston Greenpack, and Kentucky Wonder-191 were 4.9, 4.7, and 4.1, respectively. The 0.4 cm x 0.33 g treatment should be effective for evaluating cowpea germplasm for resistance to R. solani.

Last Modified: 7/25/2014