Philip D. Dukes

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.