Richard L. Fery

Development of cowpea cultivars and germplasm by the Bean/Cowpea CRSP

This paper reviews accomplishments in cowpea cultivar and germplasm development by the Bean/Cowpea Collaborative Research Support Program (CRSP) which was funded by the United States Agency for International Development for a period of about 20 years. Drought-adapted, pest and disease resistant cultivars ‘Mouride’, ‘Melakh’ and ‘Ein El Gazal’ were developed for rainfed production in the tropical Sahelian zone of Africa. Cultivars ‘CRSP Niebe’ and ‘Lori Niebe’ which have seed and pod resistance to cowpea weevil and some disease resistance were developed for rainfed production in the tropical Savanna zone of West Africa. Cultivar ‘California Blackeye No. 27’ was developed for irrigated production in subtropical California, USA and is a semidwarf with heat tolerance and broad-based resistance to root-knot nematodes and Fusarium wilt. Various cultivars with persistent-green seed color including ‘Bettergreen’ and ‘Charleston Greenpack’ were bred for use in the food freezing industry in the USA. Germplasms were developed with unique traits including: snap-type pods, green manure/cover crop capabilities, heat tolerance during reproductive development, chilling tolerance during emergence, delayed leaf senescence as a mechanism of adaptation to mid-season drought and high grain yields, differences in stable carbon isotope discrimination, harvest index, rooting and plant water- and nutrient-relations traits, broad-based resistance to root-knot nematodes and Fusarium wilt, and resistance to flower thrips, cowpea aphid, lygus bug and cowpea weevil, and various quality traits including all-white and sweet grain. These germplasms provide a valuable resource for breeding additional cowpea cultivars for Africa and the USA.

Southern blight (Sclerotium rolfsii Sacc.) of cowpea: yield-loss estimates and sources of resistance

Abstract Replicated field studies were conducted over a three-year period to assess the yield-reducing potential of southern blight (Sclerotium rolfsii) on cowpea, and to evaluate the range of genetic variability in cowpea germplasm for resistance. Southern blight was shown to have a considerably greater impact on dry-seed yields than that suggested by a review of the published literature. The disease caused a dry-seed yield loss of 53.4% in one study, and losses approaching 50% were observed for some cultivars in a second study. Reduced pod numbers likely accounted for most of the reduced dry-seed yields. There is significant variability in cowpea germplasm for resistance to southern blight. Two cultivars, Brown Crowder and Carolina Cream, exhibited promising levels of resistance in two years of testing.

Potential for utilization of pepper germplasm with a variable reaction to Sclerotium rolfsii Sacc. to develop southern blight-resistant pepper ( Capsicum annuum L.) cultivars

The bell-type pepper cultivar Golden California Wonder, a source of resistance to southern blight, was crossed with the susceptible cultivar Sweet Banana. The F 1 , F 2 and backcross progenies of this cross and the parental lines were evaluated in an inoculated field study for their reactions to Sclerotium rolfsii Sacc. A categorical rating system was used to rate plants for severity of wilting and severity of stem-lesion development. The plants within all three non-segregating populations (the resistant parent, the susceptible parent and the F 1 ) displayed a range of reactions to S. rolfsii . Variable reactions to S. rolfsii among homogeneous pepper populations were expected because this phenomenon is well documented in the literature and we had observed similar responses in field trials conducted over multiple years. The high level of variation for reactions to S. rolfsii exhibited by the parental and F 1 hybrid populations and the categorical system of rating individual plants placed severe limitations on the effective use of any quantitative type of analysis. Accordingly, a weighting procedure was used to correct the F 2 and backcross populations based on frequencies of apparent mis-classifications in the parental and F 1 populations. Examination of the comparative frequency distributions of the parental and progeny populations and examination of the weighted segregation data suggest that the southern blight resistance in ‘Golden California Wonder’ is conditioned by a single recessive gene. The level of resistance conditioned by this reputed recessive gene appears high enough to recommend it for use in pepper breeding programmes.

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

Field studies were conducted to characterize the genetic nature of resistance to southern blight (caused by Sclerotium rolfsii Sacc.) exhibited by the cowpea [Vigna unguiculata (L.) Walp.] cultivars Carolina Cream and Brown Crowder and to determine if a genetic relationship exists for this resistance between the two cultivars. 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 indicates 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.