AUTHOR=Boukar Ousmane , Abberton Michael , Oyatomi Olaniyi , Togola Abou , Tripathi Leena , Fatokun Christian 

TITLE=Introgression Breeding in Cowpea [Vigna unguiculata (L.) Walp.]

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.567425

DOI=10.3389/fpls.2020.567425

ISSN=1664-462X

ABSTRACT=ABSTRACT
The narrow base of genetic diversity characteristic of cowpea can be attributed to its being self-pollinating, evolving from narrow wild germplasm and exhibiting very limited gene flow between wild and cultivated types. Backcrossing to introduce simply inherited desirable traits and utilization of improved breeding lines and varieties as parents in crossing pro-grams further encouraged narrowing of cowpea varieties’ genetic base. In most cowpea breeding programs genes for some resistance and market traits were pyramided into lines characterised by good levels of acceptance to farmers and consumers. Besides predisposing widely distributed improved varieties to genetic vulnerability, narrow base of genetic variation may be contributing to the plateauing in cowpea grain yield which compromises genetic gains in varieties being developed. Cross compatible wild relatives have not been used in variety development because breeders shy away from them due to their tiny seed sizes, unattractive seed coat colour and texture, pod shattering and susceptibility to viruses. A number of wild cowpea relatives, both within and outside section Catiang of Vigna species, have been evaluated by researchers for their reactions to cowpea insect pests and diseases. Vigna vexillata lines tested were resistant to the legume pod borer (Maruca vitrata), the cowpea weevil (Callosobruchus maculatus) and Striga gesnerioides but are cross incompatible with cultivated cowpea. Some lines among the cross compatible wild relative V. unguiculata ssp. dekindtiana were found to be resistant to aphid in the seedling stage while others showed good levels of drought and heat tolerance. Molecular markers are being generated for use to tag quantitative trait loci (QTL) with effects on some desirable attributes in cowpea. Modern breeding tools, including transgenics, can be applied for the improvement of cowpea bypassing the natural barriers of traditional breeding. Transgenic cowpea with Bt gene cry1Ab and showing resistance to M. vitrata has been released in Nigeria. Genome editing, an emerging powerful tool, can also be used for developing improved cowpea varieties with durable resistance to pests and diseases.