Genetic engineering approaches for drought tolerance in grain legumes: progress and prospects

Inadequate water resources and the ensuing climate change over the recent years are posing major challenges for food production. Drought in various forms is responsible for major losses to global crop production, affecting millions of resource-poor farmers in the semi-arid tropics. While developing drought-tolerant cultivars could alleviate such economical strains, genetic improvement of grain legumes is difficult to achieve through conventional means due to their highly self-pollinating characteristics and conserved genomes with very little variability. To generate additional genetic diversity, we attempted to enhance drought tolerance in chickpea and peanut through genetic engineering approaches. Independent transgenic events with high transpiration efficiencies (TE) and desirable root and shoot traits were selected for further evaluation under a series of environments under glasshouse and confined field trials to comprehensively study the component traits of drought, and understand the stress adaptive mechanisms. Relationship between TE and its surrogate traits were explored, besides studying the role of biochemical changes in the anti-oxidative machinery under water-limiting conditions. Evaluations were based on water capture, effective use of captured water for producing biomass via photosynthesis, and converting assimilates into harvestable yield. Accordingly, critical assessment of drought tolerance and yield under contained field conditions proved the effectiveness of several events that showed substantial yield improvement under drought stress, without any accompanying yield penalty under irrigation. Details of various strategies to develop drought tolerant transgenc plants, and the results and scope of our own studies will be discussed.