Molecular breeding of groundnut for enhanced productivity and food security in the semi-arid tropics: opportunities and challenges

About 94% of the world groundnut (Arachis hypogaea L.) production comes from the rainfed crop grown largely by resource-poor farmers. Several biotic and abiotic stresses limit groundnut productivity, together causing annual yield losses of over US $ 3.2 billion. The Arachis species harbor genes capable of improving both seed yield and quality in addition to imparting high levels of resistance to diseases and insect pests. Many of the wild Arachis species are not cross compatible with cultivated groundnut. However, efforts to overcome incompatibility in wide crosses have started to liberate resistance genes in interspecific progenies. But these progenies carry a lot of linkage drag. Marker-assisted backcross breeding should minimize the linkage drag as it greatly facilitates monitoring of introgressed chromosome segments carrying beneficial genes from wild Arachis to cultivated groundnut. Transgenic groundnuts with resistance or tolerance to biotic and abiotic stresses have been produced and are in various stages of characterization under containment and/or controlled field conditions. Once favorable genes are introduced into cultivated groundnut through wide crossing and/or genetic transformation techniques, these genes will become ideal candidates for marker-accelerated introgression. DNA marker based genetic linkage map should enable breeders to effectively pyramid genes for good seed quality and resistance to biotic and abiotic stresses into agronomically enhanced breeding populations in a much shorter time than would be possible by conventional techniques. To date 110 SSR markers detected genetic variation in a diverse array of 24 groundnut landraces. However, substantial efforts are still required to develop sufficient PCR-based markers, particularly SSRs and SNPs, for the construction of high-density genetic linkage map and for the routine application in the molecular breeding in groundnut. The use of automated technologies will become increasingly important for large-scale germplasm characterization and realistic scale marker-assisted selection in groundnut. An international legume genomics initiative has been formed between USA Universities and the International Agricultural Research Centers of the Eco-Regional Alliance on legumes to translate the benefits of the "consensus legume genome" for rapid impacts on the genetic improvement of tropical legumes