Diallel analysis of sweetpotatoes for resistance to sweetpotato virus disease

Abstract

Sweetpotato virus disease (SPVD) is due to the dual infection and synergistic interaction of Sweetpotato feathery mottle potyvirus (SPFMV) and Sweetpotato chlorotic stunt crinivirus(SPCSV), and causes up to 98% yield loss in sweetpotato in East Africa. This study was conducted to determine the inheritance of resistance to SPVD in sweetpotato and to estimate the nature of genetic variance. Ten parental clones varying in reaction to SPVD were crossed in a half diallel mating design to generate 45 full-sib families. The families were graft-inoculated with SPCSV and SPFMV to induce SPVD and evaluated for resistance in a randomized complete block design at two sites in Namulonge, Uganda during 1998–2000. In serological assays for SPFMV and SPCSV,resistance to symptom development and recovery from initial systemic SPVD symptoms, characterised resistant genotypes. Genetic component analysis showed significant effects for both general combining ability (GCA) and specific combining ability (SCA) for resistance to SPVD. GCA to SCA variance component ratios were large (0.51–0.87), hence GCA effects were more important than SCA effects. Resistant parents exhibited high GCA indicating that additive gene effects were predominant in the inheritance of resistance to SPVD and recovery. Narrow-sense heritability (31–41%) and broad-sense heritability (73–98%) were moderate to high, indicating that rapid genetic gains for SPVD resistance could be accomplished by mass selection breeding techniques. Two genotypes, New Kawogo and Sowola, had high negative GCA effects and had several families in specific crosses,which exhibited rapid recovery from SPVD,and are promising parents for enhancement of SPVD resistance and recovery.