Abstract
An evaluation of crosses between vegetable and field cowpea for resistance to the cowpea Bruchids, [ Callosobruchus maculatus (F)], was carried out at the Enugu State University of Science and Technology, Enugu southeastern Nigeria. There was a significant difference in the field infestation of the cowpea lines by C. maculatus . AD-36-WB had the highest percentage field infestation by the insect pest, whereas, AE—36-C X AN-16-D, and AN-14-D were free from the field infestation by the pest. Vegetable cowpea lines tested had some levels of resistance to the cowpea Bruchid and the gene responsible for the resistance were successfully transferred from vegetable cowpea to the susceptible field cowpea by cross-breeding techniques. No vegetable cowpea tested had complete resistance to the cowpea bruchid, however, they had lower susceptibility than the field cowpea tested. Reduction in the relative susceptibility of the cowpea to C. maculatus was achieved by cross breeding field cowpea with vegetable types. For instance, in crosses between AD-36-W (field cowpea) and AE-36-C (vegetable cowpea), AD-36-WB (field cowpea) and AN-14-D (vegetable cowpea), AD-36-W (field cowpea) and AE-36-F (vegetable cowpea), AD-36-WB (field cowpea) and AE-36-C (vegetable cowpea), AN-14-D and AE-36-F reduced susceptibility of AD-36-W and AD-36-WB to C. maculatus from 63.59% to 51.09%, 68.46% to 59.09%, 63.59% to 47.38% and 68.48% to 38.84% respectively. Also, gene responsible for susceptibility to the storage insect pest were successfully transferred from field cowpea to the vegetable cowpea through cross-breeding techniques. A cross between two vegetable types namely; AE-36-C and AN16-D had the least susceptibility level of 24.32%. There was a significant difference in mean number of eggs laid per cowpea line with AD-36-WB recording the highest mean number of 134.75 eggs and AE-36-F recording the least mean number of 4.75 eggs. There was also a significant difference in the percentage adults emergence per cowpea line with AD-36WB having the highest percentage of 68.46% adults, and AE-36-C X AN-16-D having the least percentage of 24.32% adults. The result of the experiment also showed a significant difference in mean longevity of female adults reared from cowpea lines with those reared from AD-36WB X An-14-D, and AE-36-C having the highest mean longevity of 14 days each whereas those from AD-36WXAE-36-C had the least mean longevity of 5.6 days. Also, there was a significant difference in mean testa thickness of the seeds tested with AE-36-C having the highest mean testa thickness of 0.20mm, whereas AD-36-WB had the least mean testa thickness of 0.02mm. However, there was no correlation between either testa thickness or moisture content and levels of infestation by the storage insect pest. Again, there was a significant difference between mean weight loss of seeds tested after infestation by C. maculatus , with AD-36WB recording the highest mean weight loss of 0.38g, whereas AE-36-C and AE-36-F, had the least mean weight loss of 0.07g. There was a positive correlation between the weight loss of the adult C. maculatus and the weight (g) of the seeds from which the insect pest was reared (r = 0.03). Key words: Cowpea lines, cross-breeding, Callosobruchus maculatus , resistance, susceptibility
Highlights
Cowpea (Vigna unguiculata (L.) Walp) is an important legume in many developing countries (Adams and Baidoo 2008) and are grown mainly for its grains (Fatokun, 2002)
Percentage field infestation of cowpea lines by Callosobruchus maculatus Post harvest investigation showed that all the cowpea lines except AE-36-C X AN-16-D and AN-14-D were infested in the field by the insect pest
It means that increase in the resistance of field cowpeas to C. maculatus was reduced by cross-breeding them with vegetable cowpeas
Summary
Cowpea (Vigna unguiculata (L.) Walp) is an important legume in many developing countries (Adams and Baidoo 2008) and are grown mainly for its grains (Fatokun, 2002). Several attempts to preserve the seeds majorly through chemical means apart from being expensive sometimes result in the poisoning of cowpea and environmental toxicity (Olakojo et al, 2007) This suggests the need for alternative management method that would protect the crop and the environment (Oluwafemi et al 2013). It is in this direction that this research work was designed to (i) test crosses between vegetable and field cowpeas for resistance to the cowpea bruchid (Callosobruchus maculatus) to ascertain whether vegetable cowpeas have some resitance to this storage pests (ii). It is in this direction that this research work was designed to (i) test crosses between vegetable and field cowpeas for resistance to the cowpea bruchid (Callosobruchus maculatus) to ascertain whether vegetable cowpeas have some resitance to this storage pests (ii). find out whether the resistant traits (genes) can be transferred to the susceptible ones (field cowpeas) by cross breeding as a means of finding a lasting solution to the menacing activities of this storage pest of cowpeas. (iii) attempt to elucidate the nature of resistance through studying the effect of the cowpea lines on the longevity of the insect pest
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