Reaction of cowpea cultivars to Rhizoctonia solani in field tests

Rhizoctonia solani is the primary cause of seed rot, damping-off, and root rot in cowpea (Vigna unguiculata) in the southern U.S. and causes substantial yield losses worldwide. Nine cowpea cultivars were evaluated for reaction to R. solani in inoculated field tests at six planting dates in Charleston, SC in 2004. The cultivars evaluated were Bettergro Blackeye, Knuckle Purple Hull, Mississippi Silver, Colossus-80, Charleston Nemagreen, Texas Cream-40, White Acre, Coronet, and Charleston Greenpack. Tests were planted on 20 April, 29 April, 11 May, 19 May, 27 May, and 8 June. The experimental design for each test was a split-plot with six replicates. Whole plots were cultivars, and sub-plots were inoculation with R. solani and an uninoculated control. Rhizoctonia solani caused significant seedling losses in five of six planting dates and seed yields were reduced in the 11 May planting. Overall, standard cowpea cultivars (Mississippi Silver, Colossus-80, and Coronet) had higher stand counts and heavier seed yields than other cowpea cultivars, although these standard cultivars were not resistant to R. solani. Resistant cowpea cultivars are needed to allow earlier planting of the crop in cold soils, which would extend the growing season and allow more efficient use of harvesting equipment and processing facilities.