Evolution of the breeding system in cowpea (Vignaunguiculata (L.)Walp.) and its implications in the improvement techniques
1977
Ladeinde, T.A.O., Department of Agricultural Biology, University of Ibadan, Ibadan (Nigeria)
Cowpea, Vigna unguiculata (L.) Walp. is believed to have originated in Africa with its centre of diversity in India. The wild types have large coloured, bilaterally symmetrical, sweetly scented flowers with well developed nectary suggesting that the plant must have been originally adapted for cross pollination by large insects e.g. bees. These wild types, however, evolved into the present cultivated inbreeding types by becoming cleistogamous i.e. fertilization takes place before the flowers open. Other outcrossing characteristics still retained in the inbreeding cultivated types include the production of sticky pollen grains with reticulate design on the exine and the presence of various forms of male sterile genes in the population with a broad genetic base and increased variability. Adapted characteristics were selected for and preserved under specific environmental conditions as the plant evolved into inbreeding types. However, the ability to maintain a small percentage of outcrossing in the cultivated varieties has a tremendous evolutionary advantage since variability could be maintained and the plant could adjust to local environmental changes. It is proposed that this evolutionary scheme be adapted for breeding improved varieties by using population improvement techniques for the base population, selecting under specific environmental conditions with emphasis initially on polygenic traits and introducing simply inherited traits later by back-crossing and further selections. The present limitations to this scheme are also discussed.
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