Progress in Genetic Engineering of Cowpea for Insect Pest and Virus Resistance

Cowpea [Vigna unguiculata (L.) Walp.] is an important staple legume, grown in many parts of the world for human and animal consumption. However, its production is severely constrained by infestation of insect pest and viruses. Genetic resources in cowpea are very limited, and they lack sufficient level of resistance to pathogens, especially the most damaging insect pests and viruses. Breeding insect pest and virus resistance have met with limited success. Biotechnological intervention for improving host plant resistance has been the most attractive for sustainable management of Maruca pod borer, storage pest bruchid species, and cowpea infecting Begomoviruses. In this review, we describe the major insect pests and viral diseases of cowpea, and the molecular basis of transgenic resistance. We highlight the recent successes in developing transgenic cowpea for both insect pest and virus resistance. Evaluation of Bt cowpea through multi-location field trials in sub-Saharan African countries with observed high insect mortality brings in renewed expectations among poor farmers in enhancing cowpea yield and income through better insect pest management. RNA silencing technology has been successfully implemented in developing cowpea resistant to MYMIV (Mungbean yellow mosaic virus), CPSMV (Cowpea severe mosaic virus), and CABMV (Cowpea aphid-borne mosaic virus). We also discuss the opportunities lie in precision genome editing and RNAi to confer cowpea molecular immunity against viruses and insect pests.