Abstract
The bruchid, Callosobruchus maculatus (F.) is one of the most destructive pests and causes substantial losses to cowpea during storage in tropical and subtropical regions. The development of successful breeding strategy requires knowledge on gene action and trait inheritance in local and improved sources. In this study, the mode of inheritance, the types of gene action and maternal effects of cowpea resistance to bruchid was investigated. Nine parental lines and their 72 F2 segregating populations, created in a full diallel Griffing’s method 1 approach, were evaluated for resistance to bruchid attack in a randomized complete block design (RCBD) with three replications. Data were recorded on number of eggs laid by the bruchid (NE), adult bruchid emergence (NEI), median development period (MDP) and Dobie Susceptibility index (DSI) was computed. Genotype had highly significant effects on NE, NEI and MDP and DSI. General combining ability (GCA) effects of parents, specific combining ability (SCA) effects of crosses, and maternal and reciprocal effects were highly significant for all the traits. The ratios of GCA to SCA for all the traits were greater than 50% suggesting the preponderance of additive over non-additive gene action in the expression of the traits. Narrow sense heritability estimates were 64.12, 77.69 and 80.99% for NE, NEI and MDP, respectively. Parents 2419, TVu-2027 and IT84s-2246 were identified as promising general combiners for resistance to bruchid and the seven best selected crosses based on their SCA and DSI values were, IT84s-2246 × 2419, 2419 × MU9, TVu-2027 × SECOW2W and 2419 × IT90K-76, 2419 × WC69, 2419 × SECOW5T and 2419 × SECOW2W. The selected parents and/or crosses could be valuable genetic materials for breeding cowpea resistance to bruchid in Uganda or similar environments. Key words: Additive gene action, heritability, median development period, reciprocal effects.
Highlights
Nine cowpea genotypes comprising of five bruchid resistant (IT90K76, IT97K-499-35, TVU-2027, 2419 and IT84s-2246) and four susceptible (SECOW2W, WC69, MU9 and SECOW5T) lines used as parents were selected from out of 145 cowpea genotypes by a no-choice laboratory bruchid damage bioassay (Miesho et al, 2018)
Values of Baker’s ratio estimated for all the traits were greater than 50% suggesting the predominance of additive over non-additive gene action in the expression of these traits
The results showed that the inheritance of number of eggs, number of insect emergence, and median development period traits were predominantly controlled by additive gene actions (Table 4)
Summary
Walp.) (Fabaceae) is one of the most important legume crops in arid and semiarid regions of Africa (NRC, 2006). It is a warm-weather crop, drought tolerant and well- adapted to the drier regions. Despite its relevance to agriculture in the developing world and its stress resilience, actual yields of cowpea are much lower than the known yield potential (Amatriaín et al, 2016). Production of this important crop has been constrained by insect pests among other factors (Boukar et al, 2012) and devastating effects in storage due to bruchid (Adebayo and Anjorin, 2018)
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