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Title: Southern Blight (Sclerotium rolfsii Sacc.) of Cowpea: Genetic Characterization of Two Sources of Resistance

Author
item Fery, Richard
item Dukes, Philip

Submitted to: International Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2011
Publication Date: 9/30/2011
Citation: Fery, R.L., Dukes, P.D. 2011. Southern Blight (Sclerotium rolfsii Sacc.) of Cowpea: Genetic Characterization of Two Sources of Resistance. International Journal of Agronomy. Vol 2011, Article ID 652404, 6 pages, 2011. doi:10.1155/2011/652404.

Interpretive Summary: Southern blight, a stem disease incited by the pathogen Sclerotium rolfsii Sacc., is a major disease of cowpea. The disease decreases plant vigor and can reduce seed yield by over 50%. Two horticultural-type varieties, Carolina Cream and Brown Crowder, have been reported to exhibit promising levels of resistance to southern blight. Since the breeding value of any disease-resistant germplasm would be enhanced greatly if the mode of inheritance was understood, ARS scientists at Charleston, SC, initiated studies to determine the inheritance of the southern blight-resistance exhibited by cowpea varieties Carolina Cream and Brown Crowder. The results of these studies indicate that the resistance in both varieties is conditioned by a single dominant gene. This means that the development of southern blight resistant varieties of cowpea is a very feasible objective for cowpea breeding programs. The incorporation of a southern blight resistance gene into the various types of cowpea varieties would give American farmers an effective, economical, and environmental friendly way to control a major cowpea disease problem.

Technical Abstract: Field studies were conducted to determine the inheritance of resistance to southern blight (caused by Sclerotium rolfsii Sacc.) exhibited by the cowpea [Vigna unguiculta (L.) Walp.] cultivars Carolina Cream and Brown Crowder, and to determine if a genetic relationship exists for this resistance between the two cultivars. ‘Carolina Cream’ and ‘Brown Crowder’ were each crossed with the susceptible cultivar Magnolia Blackeye. The F1, F2, and backcross progenies of these crosses and the parental lines were evaluated in inoculated field studies for reaction to S. rolfsii. Additionally, the resistant cultivars Carolina Cream and Brown Crowder were crossed with each other, and the F1, and F2 progenies and the parental lines of this cross were evaluated for reaction to S. rolfsii. Examination of the comparative frequency distributions of the parental and progeny populations of the ‘Carolina Cream’ x ‘Magnolia Blackeye’ and ‘Brown Crowder’ x ‘Magnolia Blackeye’ crosses and the corresponding segregation data suggests that the southern blight resistances exhibited by ‘Carolina Cream’ and ‘Brown Crowder’ are conditioned by single dominant genes. Examination of the segregation data from the parental and progeny populations of the ‘Carolina Cream’ x ‘Brown Crowder’ cross suggests that the two resistance genes are not allelic. The availability of each of the resistance genes in cultivar-type genetic backgrounds should allow for rapid incorporation of southern blight resistance genes into other cowpea cultivars by the application of conventional plant breeding methodologies.