The Complex Interactions of Common Bean ( Phaseolus vulgaris L.) with Viruses, Vectors and Beneficial Organisms in the Context of Sub-Saharan Africa

Common bean ( Phaseolus vulgaris L.), the world’s most widely grown legume crop, is not only of great commercial importance but is also a vital smallholder crop in low-to-medium-income countries. In sub-Saharan Africa common bean provides consumers with a major proportion of their dietary protein and micronutrients. However, productivity is constrained by viruses, particularly those vectored by aphids and whiteflies, and problems are further compounded by seed-borne transmission. We describe common bean’s major viral threats including the aphid-transmitted RNA viruses bean common mosaic virus and bean common mosaic necrosis virus, and the whitefly-transmitted begomoviruses bean golden mosaic virus and bean golden yellow mosaic virus and discuss how high-throughput sequencing is revealing emerging threats. We discuss how recent work on indirect and direct viral ‘manipulation’ of vector behaviour is influencing modelling of viral epidemics. Viral extended phenotypes also modify legume interactions with beneficial organisms including root-associated microbes, pollinators and the natural enemies of vectors. While problems with common bean tissue culture have constrained transgenic and gene editing approaches to crop protection, topical application of double-stranded RNA molecules could provide a practical protection system compatible with the wide diversity of common bean lines grown in sub-Saharan Africa.