|Dukes, sr., Philip|
Submitted to: Crop Protection Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/26/2001
Publication Date: 5/20/2002
Citation: Fery, R.L., Dukes, Sr., P.D. 2002. Southern blight (Sclerotium rolfsii Sacc.) of cowpea: Yield-loss estimates and sources of resistance. Crop Protection 21:403-408. Interpretive Summary: Southern blight, a stem disease caused by the fungal pathogen Sclerotium rolfsii, is recognized as a common disease of cowpea worldwide. Although southern blight has long been considered an important disease of cowpea, there is only a limited amount of information in the scientific literature that deals with either yield losses in cowpea attributable to the disease or resistance in cowpea to the disease. USDA scientists at Charleston, SC have completed a series of field studies demonstrating that 1) southern blight is a much more severe disease of cowpea than has been realized previously, 2) the impact of the disease on yield can be quite severe even in the absence of the classical southern blight symptoms of wilting and sudden plant death, and 3) some cowpea varieties exhibit promising levels of resistance to the disease. These results indicate that researchers and extension specialists need to rethink current variety, pesticide, and cultural practice recommendations for cowpea production. Detailed field evaluations of southern blight resistant cowpea varieties indicate that they are potentially useful by both home gardeners and farmers without any further development. Additionally, these resistant varieties should be excellent sources of resistance for breeding southern blight resistant cowpea varieties.
Technical Abstract: Field studies were conducted to determine the effects of inoculum level and time of inoculation on development of southern blight (Sclerotium rolfsii) symptoms in cowpea, to access the yield-reducing potential of the disease, to characterize the effect of the disease on various yield components, and to evaluate the range of genetic variability in cowpea germplasm for resistance. The use of a corn meal/sand media containing a low density of S. rolfsii sclerotia was shown to be an effective and efficient way to inoculate cowpea plants. The development of southern blight symptoms in inoculated cowpea plants was related to plant age, and greatest disease development can be expected when young plants (30 to 35 days old) are inoculated. Disease rating systems based on stem lesion development are much more effective than systems based on plant wilting in estimating the severity of southern blight in cowpea. Southern blight was shown to have a aconsiderably greater impact on seed yield than suggested by a review of th published literature. Reduced pod numbers accounted for most of the reduced seed yield. There is significant variability in cowpea germplasm for resistance to southern blight. Two cowpea cultivars, Brown Crowder and Carolina Cream, exhibited promising levels of resistance.