Abstract:

Solatium aethiopicum is one of the most important Solatium 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 identify
structure 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 Fl 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
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, El 8 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
prospective response to selection. Effects of specific combining ability (SCA) were significant
(GCA) where significant effects were obtained with chlorophyll content (CHL) only. In the narrow
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 El 1 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 El lxE4 (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.
Page iv of 155
sense (h2), the most highly heritable traits were identified as LPP, CHL, leaf fresh yield (LYF) and
grand mean ranged from 16.68 (for LRWC) to 70.38 % (for PH) per generation; indicating a
across and within moisture regimes for all traits studied unlike for general combining ability