Mutant library resources for legume crops and the emerging new screening technologies

The Leguminosae constitutes the second largest family of plants in the world. In the face of global climate change and reduction of cultivated land area, legumes have been attached more importance to feed the future in light of their nutritional values and environmental benefits. However, the yields of legume crops have thus far been far below their theoretical potentials. Despite that hybrid breeding and gene editing technologies have hold great promises to the improvement of crops, they are generally difficult to apply in legumes because of the anatomical constraints for making hybrids in these species and the low transformation efficiency impeding gene modifications. Mutation technologies, as an alternative, can speed up breeding and facilitate functional genomic studies in legume species, yet mutant screening technique remains a major challenge in this field. In this review, we detail the currently available mutant library resources in major legume crops following a brief introduction of the methods of mutation induction. We then revisit the current mainstream technologies for mutant screening, with focus on the new emerging next-generation sequencing-based approaches. Overall, this review provides a collection of information that dedicates to assisting legume researchers and breeders to more easily find and better utilize mutant resources for the improvement of these crops.