GODFREY SSEREMBA

GENETIC DIVERSITY AND BREEDING OF Solanum aethiopicum SHUM GROUP FOR DROUGHT TOLERANCE

ABSTRACT

Solanum aethiopicum is one of the most important Solanum species, with four morphological groups. Two of the groups, Gilo and Shum, are mainly cultivated because of their nutritional value and income generating potential for farmers in developing countries. Of focus for this study was the Shum, a leafy morphological group whose productivity and quality is directly affected by drought. Global limitations on water resource availability call for the need to develop productive varieties that are drought tolerant. This research was aimed at: (i) determining the genetic distinctiveness between Shum and its progenitor, S. anguivi (SAN); (ii) evaluating genetic diversity within Shum germplasm; (iii) identifying parental material for development of drought tolerant S. aethiopicum Shum varieties; and (iv) determining the combining ability of selected Shum group germplasm for drought tolerance. Twenty-five accessions, five of which were wild progenitors, were evaluated for morphological attributes. Similarly, clustering was used to identifystructure within 20 accessions of Shum based on 61 morphological variables. Further, Shum germplasm were evaluated to discover accessions (G) which excelled across water deficit regimes (WLs) where a split-plot arrangement was used. In order to determine the mode of gene action and combining ability for drought resistance among accessions, 24 F1 hybrids from a North Carolina II mating design were evaluated at five moisture regimes premised on crop growth stage and applied moisture as a percentage of field capacity of potting substrate. Five distinct clusters were identified; the progenitor accessions for Shum were grouped in their own cluster; and days to germination and emergence provided the best separation between Shum and SAN. Four distinct clusters were obtained within Shum where it was established that genotype discrimination is possible at seedling (seedling vigor), vegetative (leaves per plant, harvest index and plant growth habit) and reproductive (for instance basing on petal length and seed color) stages. From drought of 155 screening study, highly significant effect (p < 0.05) of at least two WLs on performance among at least two genotypes for majority of the traits was obtained; in addition to very highly significant (p < 0.001) G x WL interactions for leaf relative water content (LRWC), leaves per plant (LPP) and plant height (PH). Basing on LRWC, superior and most stable genotypes were identified as E6 followed by E12, E15, E18 and E14GP. The broad sense heritability for each measured trait for water deficit stress tolerance breeding was > 0.9 and expected genetic advance as per cent of grand mean ranged from 16.68 (for LRWC) to 70.38 % (for PH) per generation; indicating a prospective response to selection. Effects of specific combining ability (SCA) were significant across and within moisture regimes for all traits studied unlike for general combining ability (GCA) where significant effects were obtained with chlorophyll content (CHL) only. In the narrow sense (h2), the most highly heritable traits were identified as LPP, CHL, leaf fresh yield (LYF) and leaf dry yield (LYD) while leaf area (LA), leaf mass area (LMA) and LRWC were least heritable. Broad sense heritability (H2) was however, > 0.80 for all measured traits, indicating that nonadditive gene action exceeded additive gene effects (VA) for moisture deficit stress tolerance in Shum. Female parent E11 had the best GCA effects for CHL. The crosses with best SCA effects were identified as E10xE20 (for LA under well-watered), E3HxE15 (for LYF across watering environments, LRWC under drought stress and CHL under drought recovery), and E11xE4 (for LMA under drought recovery). This research established that morphological markers are useful for distinguishing the Shum from its progenitor; as well as within Shum genotypes at any growth stage. Also, genotypes with good breeding value and promising specific crosses offer vital information as basis for establishment of a breeding programme for the crop