Transgenic Strategies for Improved Drought Tolerance in Legumes of Semi-Arid Tropics

Water deficit is the most prominent abiotic stress that severely limits crop yields, thereby reducing opportunities to improve livelihoods of poor farmers in the semi-arid tropics (SAT) where most of the legumes, including groundnut and chickpea, are grown. Sustained long-term efforts in developing these legume crops with better drought tolerance through conventional breeding have been met with only limited success mainly because of an insufficient understanding of the underlying physiological mechanisms and lack of sufficient polymorphism for drought tolerance-related traits. Exhaustive efforts are being made at the International Crop Research Institute for Semi-Arid Tropics (ICRISAT) to improve crop productivity of the SAT crops by comprehensively addressing the constraints caused by water limitations. The transgenic approach has been used to speed up the process of molecular introgression of putatively beneficial genes for rapidly developing stress-tolerant legumes. Nevertheless, the task of generating transgenic cultivars requires success in the transformation process and proper incorporation of stress tolerance into plants. Hence, evaluation of the transgenic plants under stress conditions and understanding the physiological effect of the inserted genes at the whole plant level is critical. This review focuses on the recent progress achieved in using transgenic technology to improve drought tolerance, which includes evaluation of drought-stress response and protocols developed for testing transgenic plants under near-field conditions. A trait-based approach was considered, in which yield was dissected into components