This study evaluated the morphological diversity of some Nigerian accessions of Bambara groundnut. Field experiments were conducted in Nigeria in two locations and the phenotypic variation of Bambara groundnut accessions evaluated in 3 years (2017–2020) using a randomized complete block design. Twenty-eight quantitative and 10 qualitative traits were observed. Twenty-three out of the 28 quantitative morphological traits showed significant differences. TVSu-589 (28.85) and TVSu-670 (28.57) had the highest plant height; TVSu-572 (121.52), TVSu-271 (113.10) and TVSu-336 (104.15) had the highest 100-seed weight. Genetic variations were also observed in seed colour, terminal leaflet shape, petiole colour and eye pattern. Principal component analysis showed PC1 constituting 23.36% and PC2 constituting 15.76% of the total variation, while the first eight principal components with eigenvalues ≥1 revealed 77.28% of the total variation. Cluster analysis grouped the accessions into four groups. Based on yield data in this study, accessions TVSu-594, TVSu-350, TVSu-336, TVSu-1242, TVSu-129, TVSu-14, TVSu-179, TVSu-2100, TVSu-261 and TVSu-589 were the best for yield and are recommended for further evaluation to improve yield. This study showed that a wide range of diversity exists in Bambara groundnut of Nigerian origin that could be useful for further utilization of genetic resources and improvement.

In West Africa, Callosobruchus maculatus Fabricius mainly develops on cowpea (Vigna unguiculata (L.) Walpers) and sometimes on Bambara groundnut (Vigna subterranea (L.) Verdcourt). A survey on the development of a C. maculatus strain selected on cowpea was undertaken during eight generations on two local varieties of Bambara to determine their level of acceptability and suitability for the pest and its evolution over time and successive generations. When C. maculatus females were in contact with seeds from both Bambara varieties for the first time, they laid fewer eggs on these hosts in comparison with cowpea. However, females that have developed inside Bambara cv. Local Beige seeds deposited more eggs on their hosts of origin from the first generation onwards. The same result was obtained on Bambara cv. Local Striped seeds from the F4 generation onwards. Egg viability was not affected by host variability. On the contrary, the larval survival was significantly reduced on Bambara seeds. Larval survival and intrinsic rates of natural increase were improved on both Bambara varieties with successive generations in comparison to cowpea. Our results demonstrate that in a non-choice situation, C. maculatus is able to develop on both Bambara cv. and even increase its reproduction potential over successive generations, regardless of the climatic variations. The results help to better understand why C. maculatus is becoming a serious concern on Bambara in West Africa where the pest is frequently in contact with this occasional host.

Some aspects of the biology of Callosobruchus maculatus (F.) on three varieties of bambara groundnut, Voandzeia subterranea (L.) Thou and a local brown cowpea variety, Vigna unguiculata (L.) Walp were studied under ambient laboratory conditions. Egg hatchability of C. maculatus was above 90% on all the legume varieties. The mean developmental period of C. maculatus ranged from 23.7 days on cowpea to 28.5 days on the Piele kargu variety of groundnut. The percent emergence of C. maculatus ranged from 61.1% on var. Piele kargu to 89.5% on var. Piele balgu. There was a significant difference (P < 0.05) between the damage caused to the brown cowpea and the bambara groundnut varieties. However, there were no significant differences (P > 0.05) in damage among the three groundnut varieties. In experiments to assess the insecticidal potential of three plant materials against C. maculatus, Azadirachta indica (neem) seed powder showed a higher efficacy than both Citrus sinensis peel powder and the powder of Chromolaena odorata leaves. At 1.0 g per 40 g of legume seed, it was twice as effective as Ci. sinensis and Ch. odorata over a period of 40 days.