Integrating root architecture and physiological approaches for improving drought tolerance in common bean (Phaseolus vulgaris L.)

Grain legumes including common bean are mostly grown in rainfed production systems and invariably suffer from water stress at critical growth stages leading to significant yield reductions. Drought is one of the most importantstress limiting common bean productivity. The yield has been the primary breeding objective and has been improved by either targeting yield per se as well as yield components. However, yield is a highly complex trait with low heritability and screening for drought resilience based on yieldand/or secondary traits is increasingly appreciated as better approach. Drought tolerance breeding is relatively complex on account of quantitative inheritance and greater environmental influence therefore, it is imperative to identify less complex traits related to the drought that will improve upon selection for drought tolerance and separate these traits into major components that may help further understanding of the genetic basis. In most of the grain legumes breeders have concentrated on above-ground components. However, increasing experimental evidences have reinforced the premise that the hidden half of the plant including its structural and functional attributes and associated microbiome can be an effective tool for improving stress resilience. However, an improved understanding of the relationship between below and above-ground traits will contribute to improved productivity under drought stress. Among the above ground traits that have emerged as most effective surrogates are canopy temperature depression, leaf water status, stay green trait, phostosynthetic efficiency, membrane stability, limited transpiration and reproductive success and have contributed to our mechanistic understanding of plant response to stress. This paper discusses some of the aspects of root architecture and physiological traits to highlight mechanistic and applied perspectives from a plant breeding standpoint in common bean.