Fifteen elite cowpea cultivars were evaluated for their susceptibility to attack and damage by the most destructive storage pest, Callosobruchus maculatus (F.), based on the number of eggs laid, total developmental time, percentage adult emergence, seed weight loss, and growth index. Significantly, more eggs were laid on the seeds of Bengpla, California and Clemson genotypes than on those of the other cultivars. The mean developmental time (days) of C. maculatus ranged from 21.4 days on California 20 to 25.7 days on Sul 518-2 (Marfo tuya), and was significantly different between the cowpea cultivars. Adult emergence was considerably high on Bengpla, California and Clemson genotypes, but low on IT94K-445-2, Melack, and Sul 518-2. Weight loss ranged from 7 to 35.6 per cent and was significantly different between cultivars. The IT94K-445-2, IT98K-279-3 and Valenga cultivars had the least damage whilst California 11, IT87KD-1951 and Bengpla had the highest loss in seed weight. Overall, the susceptibility indices which ranged from 4.8 to 9.4 indicated that IT94K-445-2, Melack, Sul 518-2 and IT98K-279-3 were the least susceptible, whereas Bengpla, California and Clemson were the most susceptible cultivars. Therefore, it is recommended that IT94K-445-2, Sul 518-2, Melack, and IT98K-279-3 that have some degree of resistance to C. maculatus in this study should either be promoted or incorporated into breeding programmes because this will help to considerably reduce storage losses that farmers incur.
Aphids (Aphis craccivora Koch) are an important vegetative stage pest of cowpea in Africa. The use of resistant cultivars is among the best management option for this pest, but the success of this strategy is influenced by the stability of the resistant genotype to the cowpea aphid biotypes present in the major cowpea growing areas in a country. This work, therefore, aimed at identifying cultivars/genotypes with stable resistance to aphid infestation across different cowpea growing ecologies in Ghana and estimating yield loss due to aphid infestation at the seedling stage. To ascertain the stability of aphid-resistant cultivars/genotypes, four cultivars/genotypes (SARC1-57-2, SARC1-91-1, IT97K-499-35, and Zaayura) and a susceptible check (Apagbaala) were tested across 18 locations in Ghana. An on-station experiment was used to quantify yield losses due to aphid attack at the seedling stage in the five cultivars/genotypes mentioned above together with 5 additional cultivars/genotypes [i.e., IT99K-573-3-2-1, IT99K-573-1-1, Padituya, Resistant BC4F3 (Zaayura//(Zaayura × SARC1-57-2)), and Susceptible BC4F3 (Zaayura//(Zaayura × SARC1-57-2))]. The results showed that SARC1-57-2 was stable in all ecologies, in terms of its resistance to aphids; it had high vigour score (3.8 ± 0.03) and low plant mortality (3.7 ± 0.22%) compared to the susceptible genotypes. The number of days to flowering and maturity were significantly higher in aphid-infested plants than in the uninfested ones. Grain yield loss was estimated to range between 3.8 and 32.8%. Except for SARC1-57-2, Resistant BC4F3, and Padituya, the remaining cultivars/genotypes sustained significant yield losses under aphid infestation. Thus, the aphid-resistance gene in SARC1-57-2 is stable against aphids. This resistance genotype can be incorporated into cowpea improvement programmes to breed for aphid-resistant cultivars. Also, the cultivation of such improved cultivars will reduce pesticide usage in cowpea production.
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