Abstract:

Groundnut production in Uganda is rain-fed. As such, drought is a major challenge, especially when it occurs in combination with biotic stresses such as groundnut rosette virus disease. The objectives of this study were; (1) to assess smallholder farmers’ perceptions of drought in groundnut production, (2) to determine farmers’ varietal selection criteria in groundnut, (3) to assess genetic diversity of the Ugandan groundnut collection, and (4) to determine combining ability and gene action controlling drought tolerance traits and physical quality traits under different water regimes, thereby identifying parents and crosses for cultivar development. A participatory rural appraisal revealed that groundnut was grown mainly by smallholder farmers under both mono and mixed cropping systems depending on the region. Most of the farmers (>77%) from all regions indicated that the major impact of drought on their farming activity was low yields. The participatory variety selection study showed that farmers have effective methods for selecting varieties based on preferred traits. However, the farmers’ selection methods need to be complemented by breeder methods. Results of genetic diversity studies showed that 50% of the 2986 SNPs were polymorphic with a mean PIC of 0.15 for all populations combined, implying low allelic diversity in the groundnut collection. A high level of genetic relatedness was observed at population level, as individuals from all assigned populations aggregated into three clusters based on dissimilarity analysis under principal component analysis (PCA). However, a high level of genetic differentiation existed within individuals rather than among populations based on analysis of molecular variance (AMOVA) and cluster analysis. Based on structure analysis, three gene clusters were found underlying genepools for the groundnut populations used in this study. The study on genetic analysis for drought tolerance traits revealed that both additive and non-additive gene actions controlled the inheritance of the traits in groundnut. The general combining ability effects GCA) were more important than the specific combining ability (SCA) for the SPAD chlorophyll meter readings (SCMR) and harvest index (HI). This observation was similar under both drought stressed and non-drought stressed environments and for all the groundnut botanical types. The SCA effects for traits such as drought tolerance index based on pod yield, and biomass were significant. Given unlikely predominance for either additive or non-additive gene effects, the breeding procedure would require selection to be conducted in the later generations in order to harness both gene effects. In addition, significant associations between drought stressed and non-drought stressed environments were observed for SCMR, harvest index, pod yield, number of pods, leaf length, and leaf width. Therefore, since SCMR and HI are relatively stable and less influenced by environmental conditions, they can thus be measured under both drought stressed and non-drought stressed conditions. However, selection based on these traits can be done more effectively under non-droughtstressed environment. In addition, the best breeding approach would be the one that emphasizes additive gene action such as recurrent selection or simple selection by pedigree breeding. The study on gene action governing physical quality traits showed the significance of GCA, SCA and maternal effects for various traits. The genetic analysis indicated that expression of the majority of the physical quality traits was regulated by additive gene action suggesting possibility of early generation selection, while non-additive gene action also played an equally important role in the control of the physical seed traits. However, the gene control varied with botanical varieties for some traits. Among the Virginia botanical variety types, non-additive gene action was predominant for all the traits regardless of the test environment implying that botanical classification has a bearing on the parental selection in improving these traits in this subgroup of groundnuts. In cases where both additive as well as non-additive gene effects controlled the expression of the traits, the breeding strategy has to delay selection to later generations or should involve recurrent selection that favours both additive and non-additive gene action. Significant maternal effects for some traits signify the role of the maternal parent in the expression of quality traits and importance of parental selection in quality breeding. Therefore, one of the parents to be used in hybridization should have large pods and seeds for obtaining better segregants. Low but positive or negative association of drought tolerant traits with physical quality traits, regardless of stress regime, can be exploited for improving seed yield without compromising seed size. Thus, the selection of high pod yield potential under no-stress or small reduction in pod yield under drought stress should guarantee high seed size. Overall, this study has highlighted the mismatch between the release of new varieties and adoption rates despite the fact that farmers are aware of the new improved materials. Therefore, there is a need for various stakeholders to strengthen their role in the transfer of research outputs to end users (farmers). Among the key recommendations, breeders, extension staff and farmers need to work together to make the technology that has been developed to have relevancy. This study also confirmed that the groundnut genepool in Uganda has a low genetic base. However, from the information obtained from the study, future hybridizations avoiding parents sharing a common ancestry can be done or diversity can be improved by enriching the collection with some introductions from geographically different areas. Identification of genotypes with drought tolerance and/or physical quality traits helps in the quest to develop new varieties, which are well adapted, and with farmer preferred traits. The observation that additive gene effects are involved in governing drought and physical traits, besides, positive correlations between these traits indicates that drought tolerant materials can be improved by accumulating additive genes using methods that favour general combining ability such as recurrent selection breeding procedures. Where possible, molecular techniques such as genomic selection can be applied to shorten the entire process.