Shimelis, Hussein.Mashilo, Jacob.Mkhize, Phumzile.2025-10-102025-10-1020252025https://hdl.handle.net/10413/23950Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Bottle gourd (Lagenaria siceraria) is a drought-resilient cucurbit widely cultivated in sub-Saharan Africa and Asia for diverse food, nutrition, and industry uses. Its fresh leaves and fruits are consumed as vegetables, providing essential nutrients such as vitamins B, C, and E, minerals, fiber, and amino acids. The seeds serve as a source of edible oil, dietary fiber, and phytochemicals. Bottle gourd possesses significant genetic diversity, presenting opportunities for developing high-yielding and drought-tolerant varieties. However, the crop remains underresearched, primarily cultivated by small-scale farmers using unimproved landrace varieties, resulting in low productivity. Therefore, the overall aim of this study was to develop highyielding and drought-tolerant bottle gourd hybrids for commercialization in South Africa to enhance food and nutrition welfare and provide market opportunities to growers. The first part of the study quantified the concentrations of cucurbitacins in diverse bottle gourd genotypes and appraised the relationship to drought tolerance. The contents of cucurbitacins B, E, and I were quantified in leaves and roots of twelve preliminarily selected bottle gourd accessions using high-performance liquid chromatography–mass spectrometry (HPLC-MS). The contents of cucurbitacins B and I were enhanced under increased drought intensity for accessions BG-48, BG-81, and GC. In all the leaf and root samples, cucurbitacin E was not detectable. This study revealed that cucurbitacins B and I are novel biochemical markers for screening drought tolerance in bottle gourd or related cucurbits. In the second part of the study, 53 F1 hybrids were developed and field evaluated with 12 parental accessions under NS and DS conditions in two growing seasons using a 5 × 13 α- lattice design with three replicates. Data were collected on fruit yield per plant (FYPP), seed yield per plant (SYPP) and drought tolerance indices computed. Significant interactions were detected among test genotypes and water regimes for FYPP and not for SYPP. Based on tolerance indices fourteen single cross hybrids were identified as drought tolerant including BG-27 × BG-31, BG-58 × BG-78, and BG-58 × BG-80. The newly-developed bottle gourd hybrids are recommended for cultivation in drought-prone agro-ecologies in South Africa and similar environments in SSA after multi-environment testing. In the third part of the study, eight preliminarily selected and contrasting parents with drought tolerance were crossed using a half-diallel mating design. The 8 parents and 28 hybrids were evaluated under NS and DS conditions across two growing seasons. Data were collected on fruit yield and related traits and subjected to analysis of variance and combining ability. Significant (p < 0.05) specific combining ability (SCA) and general combining ability (GCA) effects were recorded for fruit yield per plant (FYPP). The SCA × environment and GCA × environment interaction effects were highly significant (p < 0.001) for FYPP and SYPP. The significant genotype × environment interactions suggest that genetic effects were affected by the test environment, necessitating multi-location testing across South Africa before making any recommendations for hybrid release. Parental genotypes BG-58 and GC recorded positive and significant GCA effects for FYPP under the DS condition, whereas GC recorded positive and significant GCA effects for FYPP under the NS condition. The two genotypes are ideal breeding parents for population development to select genotypes with high fruit and seed yields. Also, GCA was preponderant for FYPP, implying that selection-based breeding strategies can be effectively employed to improve fruit yields. Crosses BG-52 × BG-79, BG- 80 × GC, and BG-70 × GC recorded high and positive SCA effects for FYPP and SYPP under DS condition. Crosses BG-27 × GC, BG-52 × BG-79, BG-52 × BG-58 and BG-58 × BG-80 recorded high and positive SCA effects for FYPP and SYPP under NS condition. The F₁ hybrids outperformed their parent in fruit yields, confirming the effectiveness of hybridisation for improving bottle gourd performance. The newly selected families and superior ones must be subjected to multi-environment evaluation for release and commercialization in South Africa or similar agroecologies. The fourth part of the study determined the genotype-by-environment interactions (GEI) for fruit yield and related traits among eight selected F1 hybrids and four checks in five contrasting environments of varying moisture conditions using a randomized complete block design with three replications. Data were collected on days to 50% male flowering (DTMF) and female flowering (DTFF), total number of fruits per hectare (TNFH) and fruit yield per hectare (FYPH) and subjected to analysis of variance, additive main effects and multiplicative interaction (AMMI) and genotype plus genotype-by-environment (GGE) biplot models. The AMMI model revealed significant (p ≤ 0.001) effects of genotype (G), environment (E) and GEI for the studied traits. The AMMI model explained a higher (96.30%) variation for TNFH, of which G, E and GEI effects explained 49.88, 24.21 and 22.21% of the total variation, respectively. The model ascribed variations of 12.36, 73.16 and 11.41% for FYPH attributable to the G, E and GEI effects, in that order. The GGE biplot model explained 94.53 and 96.56% variations for TFYPH and FYPH, respectively. The hybrids BG-58 × BG-80, and BG-52 × BG- 58 attained high and stable FYPH under both water-limited and irrigated conditions. The identified hybrids are recommended for cultivation under rainfed and irrigated conditions in South Africa. This study offered initial insights into GEI, but broader testing across diverse locations in South Africa is recommended for more reliable conclusions. Overall, the present study revealed that cucurbitacins B and I are the novel biochemical markers for screening drought tolerance in bottle gourd. The study developed and selected promising hybrids recommended for further testing in other provinces outside Limpopo .enBottle gourd.Combining ability.Cucurbitacins.Genotype-by-environment-interaction.Yield based selection.Thesis