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

Abstract

The bell-type pepper cultivar Golden California Wonder, a source of resistance to southern blight, was crossed with the susceptible cultivar Sweet Banana. The F1, F2 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 F1) 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 F1 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 F2 and backcross populations based on frequencies of apparent mis-classifications in the parental and F1 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.