No abstract

Food security is being threatening globally as a result of climate change and depletion of natural resources. Cowpea is one of the important crops that is needed to solve the world nutrition problem. Improvement for drought tolerance in cowpea can serve to mitigate the effect of drought stress resulted from climate change. Understanding the magnitude and type of genetic variability help the breeder to determine the selection criteria and breeding methods to be used for improvement purposes under drought stress. Ten cowpea genotypes were evaluated on the field during the dry season for two years in a RCBD (r=3) under well-watered (WW) and water-stressed (WS) environments. Data were collected on both morpho-physiological and agronomic characteristics. There was significant varying degree of reduction across the parental lines evaluated for all the characters. With respect to number of pods per plant, the highest reduction (64.8%) was observed in IT99K-513-21 and the lowest (-211.7%) in IT89KD-288; for number of seeds per pods, the highest (51.4%) in IT99K-513-21, the lowest (-2.7%) in TVU7778; for 100-seed weight, the highest (50.0%) in IT97K-499 and the lowest (-1.3%) in IT93K-432-1 and for total seed weight, the highest (82.8%) in IT92KD-357-3 and the lowest (-20.8%) in Danilla. The phenotypic and genotypic coefficient of variations were larger under WS than WW. Broad sense heritability estimates ranged between 12.3% in number of branches per plant to 99.0% for number of days to 50% ripe pods under WS. This genetic variability to drought stress provides opportunity for cowpea genetic improvement.

An evaluation was conducted to understand the genetic effects of combining ability for four different morphological traits, on 42 hybrids in randomized complete block design with three replications in water-stressed and well-watered environments. The significance of the additive variance (D) and dominance variance (H 1 ) indicated the presence of both additive and nonadditive gene actions in both environments. Among the parents, there was asymmetrical distribution of positive and negative dominant genes and the preponderance of overdominance gene action for all the traits in both environments. This study also indicated a minimum of ten genes for plant height in water-stressed environment and minimum of three and eight genes for terminal leaflet area and number of leaves per plant in both environments, respectively. Estimates of narrow-sense heritability ranged from 13.0% for number of branches per plant in water-stressed to 95.0% in well-watered environment for terminal leaflet area. The study revealed that Danilla, IT93K-432-1, and IT97K-499-35 were the best general combiners for all traits, Danilla × IT97K-499-35, and Danilla × IT93K-432-1 were found to be the best specific combiners for all traits in water-stressed environment. Genetic interactions, additive × additive and additive × dominance, were more pronounced in the inheritance of the traits. This indicated that the selection for these traits should be delayed till advanced generations.

An experiment was conducted to determine the extent of heterosis (a better parent and standard check) in cowpea [Vigna unguiculata (L.) Walp] under drought stress. It was performed in the Department of Crop Protection and Environmental Biology at the University of Ibadan during the 2012 to 2013 and 2013 to 2014 dry seasons between October and February. Ten parents and 42 hybrids with diverse drought tolerance were planted in a randomized complete block design (r = 3) under water‐stressed and well‐watered environments. Out of the 42 hybrids studied, the majority had significant heterosis over their better parental and standard check values, suggesting the effects of nonadditive gene actions for these traits under both environments. Significant positive heterosis over better parent (14) and standard check (19) hybrids was observed for plant height under water stress, likely due to parental combination and environmental factors. For heterosis over better parents, 15 and 23 hybrids were observed for number of days to 50% flowering, 22 and 20 hybrids for number of days to 50% ripe pod and for standard check, 10 and 22 hybrids for number of days to 50% flowering, and 20 and 33 hybrids for number of days to 50% ripe pod under water‐stressed and well‐watered environments, respectively. A substantial number of hybrids indicated highly positive significant heterotic values over better parents and standard check for terminal leaflet area, number of leaves plant−1, pod length, 100‐seed weight, total seed weight, number of pods plant−1, and number of seeds pod−1 under both environments.

This research was undertaken to assess genetic control and combining effects of some essential traits of yield under drought stress. Forty-two hybrids under water-stressed and well-watered conditions were tested in field experiments for two years. Evaluation of the various genetic components of variation was performed. Both the additive (D) and the dominant (H1) variance components were important in most of the traits suggesting both additive and non-additive gene effects under both conditions. The study showed that the minimum number of genes under water-stressed (WS) conditions ranged from 0.02 for pod length to 16.13 for days to 50% flowering. The narrow-sense heritability ranged from 24% for the number of pods per plant and pod length to 66% for the number of days to 50% flowering under WS condition. The impacts of SCA and GCA have been determined. In both conditions IT93K-432-1 and IT97K-499-35 showed the strongest GCA results on both of the traits. Danila×IT93K-432-1, Danilla×IT97K-499-35, and TVu7778×IT99K-573-2-1 have been observed to have the best SCA effect under both conditions for most of the traits. In most traits, additive and nonadditive gene effects plus additive × additive and additive × dominance gene interactions were common. In summary, additive and non-additive gene actions were detected; however, there was a preponderance of non-additive gene action in both conditions. As a result, the enhancement of these traits would involve a repetitive selection technique as a result of the prevalence of the dominant gene effect, which would allow favorable recombination of the genes in both conditions in later generations.