| dc.description.abstract | Cowpea Vigna unguiculata (L) is an important indigenous legume crop providing dietary
protein, minerals, carbohydrates, fats, vitamins and income to many people in Africa, Asia,
Central and South America. It is an important food security crop in Sub-Saharan Africa (SSA)
and a highly cherished crop for resource poor farming communities in Uganda either as a food
and cash crop. However, the production of cowpea is constrained by biotic and abiotic stresses
and among the abiotic constraints, drought is most limiting. In Uganda cowpea is mainly grown
in the Northern and Eastern regions that are prone to drought and this makes drought the major
constraint to cowpea production. Available conventional breeding methods are cumbersome and/
or consume a lot of time and resources and thus there was need to evaluate genotypes from the
mini-core collection at Makerere University for their response to drought stress and determine
the genetic basis of drought tolerance in the mini-core collection. The specific objectives of this
study were to identify cowpea genotypes tolerant to drought from the mini-core collection at
Makerere University and to identify genomic regions and candidate genes associated with
tolerance to drought in cowpea. The experiment was conducted at the National Crops Resources
Research Institute Namulonge (NaCRRI) in an alpha lattice design 10 blocks x 24 plots with two
replications with two treatments (drought stress and non-drought stress) in a screen house. Two
hundred and forty (240) cowpea genotypes from the mini-core collection were evaluated and as a
result genotypes showed considerable variability in tolerance to drought and were significantly
different for Phi2, PhiNPQ and SPAD at (P≤ 0.001), number of seeds per pod, number of pods
per plant and seed weight at (P≤ 0.001). There was a strong significant negative correlation
between Phi2 and PhiNPQ (r = -0.97) at (P≤ 0.001). PhiNPQ also negatively correlated with
SPAD (-0.3) at (P = 0.05). Broad Sense Heritability estimates showed that there was a medium
to high heritability for photosynthetic traits under drought stress and non-drought stress
conditions respectively. SPAD showed a high heritability estimate under both drought stress and
non-drought stress and hence selection for SPAD can be done under both drought and non-
drought conditions. As a result, 10 genotypes (Tvu-14224, Tvu-13939, WC-37, Tvu- 7642, IT
83-15442, KWP-17, Tvu-7755, Tvu-6365, Moussa local and IT 97K-499-35-1-1) were identified
as being tolerant to drought, suggesting that they could serve as parental lines for cowpea
tolerance to drought. Genome wide association study identified 48 genomic regions associated
with tolerance to drought. Further gene prediction analyses using phytozome V1.2 identified 6
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candidate genes which were associated with photosynthetic traits associated with tolerance to
drought which included (i) Vigun09g248500 for Phi2, PhiNPQ and PhiNO, (ii) Vigun08g010400
for Phi2, (iii) Vigun09g183400 and Vigun08g066500 for SPAD, (v) Vigun05g152700 and
Vigun09g024200 for Phi 2, PhiNPQ. The identified candidate genes regulate plant responses to
drought stress through maintaining cellular cation homeostasis. The existence of 48 genomic
regions and 6 candidate genes associated with tolerance to drought provided adequate
information for implementation in cowpea breeding programs, mainly for improving tolerance to
drought. The identified candidate genes will be incorporated into susceptible but preferred
cowpea genotypes, for development of elite lines, using SNP markers linked to these genes
through Marker Assisted Breeding. | en_US |
