Physico-chemical Properties and Resistance of Ten Bambara Groundnut (Vigna subterranea) Varieties to Attack by Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) in the Sudano-sahelian and Sudano-guinean Zones of Cameroon

Aims: This research aimed at selecting indigenous Bambara groundnut varieties with high nutritional value and inherent resistance to insect attack for cultivation in sudano-sahelian (SS) and sudano-guinean (SG) zones of Cameroon.

Study Design: The susceptibility of varieties to insect attack was assessed by adopting the standard evaluation of Dobie index and the experiment was arranged in a completely randomized design (CRD) with five replications.

Place and Duration of Study: Department of Biological Sciences (laboratory of Applied Zoology), UIT (laboratory of food chemical engineering) at Ngaoundere (SG zone). The work was also carried-out at Maroua (SS zone), starting from Jun to October 2013 for susceptibility assessment and from March 2014 to April 2015 for physico-chemical characterization of varieties.

Methodology: Ten Bambara groundnut genotypes were infested with bruchids for six days. Comparative data on the mean percentage adult emergence, mean developmental period and susceptibility index (SI) were then collected for analysis. Seeds were also analyzed for physical and chemical properties to study the physico-chemical basis of resistance to bruchid attack and the nutritional value.

Results: Varieties were significantly different regarding their physical properties (F = 13.32 – 92.89; P ˂ 0.001), chemical composition (F = 6.57 – 2936.00; P ˂ 0.001 – 0.01) and susceptibility index (F = 107.02 – 152.59; P ˂ 0.001). Overall, SS zone was most suitable for insect development. Biophysical characteristics were not found important to characterize the susceptibility of varieties to insect attack. Carbohydrates were negatively correlated (r = -0.53) with Bambara groundnut SI under SS conditions, while total polyphenolic compounds were positively correlated (r = 0.52) under SG conditions. Galaji, Black eye and Guerade guerlal consistently demonstrated high tolerance to infestation by C. maculatus and therefore, may be recommended for relatively longer storage.

Conclusion: The physical parameters of the grains did not linearly relate with varietal resistance to C. maculatus. However, it may be inversely or directly correlated with chemical characteristics, depending on the agro-ecological zone. Further analyses of grain biochemical components that may relate to varietal resistance to C. maculatus are required. From the results of the present finding only two (Galaji and Black eye) and three (Guerade guerlal, Galaji and Black eye) varieties were resistant to bruchids attack respectively in SS zone and SG zone, of the ten varieties tested. Seed legumes suffer from heavy damage by cowpea weevil attack during storage in SS than in SG zone of Cameroon (Northern Cameroon). Nevertheless, Galaji and Black eye may be recommended for relatively longer storage to achieve the goal of long term and sustainable pest management strategies in Northern Cameroon in general.

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