Inheritance of rosette virus disease resistance among early maturing groundnut accessions in Uganda.

Abstract

Groundnut rosette disease (GRD) has long been regarded as a major limiting biotic constraint to groundnut production restricted to Sub Saharan Africa (SSA). The disease has been reported to be caused by a complex of three viral components that interact in synergistic fashion resulting into severe crop losses. Being aided by the aphid vector (Aphis craccivora Koch), the viral component has been persistently spread through disease epidemics hence negatively impacting farmers and rural livelihood in SSA. Continued efforts to develop resistant groundnut cultivars are critical in SSA where the disease appears to be restricted. In response, studies presented in this thesis contribute towards understanding the genetics of inheritance of GRD resistance among early maturinggenotypes in Uganda. Three resistant (Serenut 2, Serenut 3 and Serenut 8) and four local (Acholi White, Egolomoit, Red Beauty and Serenut 1) genotypeswere used as genetic materials for this study. The levels of resistance to GRD among the exotic and local parental material were determined. Two major phenotypic classes were revealed; the resistant and susceptible class. Serenut 2 was identified as the most resistant parent and Serenut 1 the most susceptible parent. F1 Crosses were generated from the parental material using the North Carolina 2 mating scheme and these were advanced to F2 through selfing. Results from F2 progeny evaluation indicated that additive and non additive gene action were key in the genetic control of GRD among the crosses. Egolomoit contributed strongly towards resistance to GRD while Red Beanty was the worst general combiner. Heritability studies revealed high broad sense heritability based on disease severity data, a moderate baker’s ratio and transgressive segregation suggesting a quantitative mode of gene action. In conculsion, this work has revealed that resistance to GRD is conditioned by both additive and non additive gene effects that may be quantitatively inherited and that possibilities of improving local landraces exist and thus could exploited through crop breeding.