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Terminal drought stress affects more than half of the areas planted with common bean (Phaseolus vulgaris), the main food legume globally, generating severe yield losses. Phenotyping water deficit responses and water use are central strategies to develop improved terminal drought resilience. The exploration and exploitation of genetic diversity in breeding programs are gaining importance, with a particular interest in related species with great adaptation to biotic and abiotic factors. This is the case with tepary beans (Phaseolus acutifolius), a bean that evolved and was domesticated in arid conditions and is considered well adapted to drought and heat stress. Under greenhouse conditions, using one genotype of tepary beans (resistant to drought) and two of common beans (one resistant and one susceptible to terminal drought), we evaluated phenotypic differences in traits such as water use efficiency (WUE), transpiration efficiency, rate of photosynthesis, photosynthetic efficiency, stomatal density, stomatal index, stomatal size, and the threshold for transpiration decline under well-watered and terminal drought conditions. Our results indicate two different water use strategies in drought-resistant genotypes: one observed in common bean aimed at conserving soil water by closing stomata early, inhibiting stomatal development, and limiting growth; and the other observed in tepary bean, where prolonged stomatal opening and higher carbon fixation, combined with no changes in stomata distribution, lead to higher biomass accumulation. Strategies that contribute to drought adaptation combined with other traits, such as greater mobilization of photoassimilates to the formation of reproductive structures, confer bean drought resistance and are useful targets in breeding programs. [ABSTRACT FROM AUTHOR]

Drought substantially limits seed yield of common bean (Phaseolus vulgaris L.) in the tropics. Understanding the interaction of drought on yield and the nutrient concentration of the seed is vital in order to supply nutrition to the millions of consumers who rely on common bean as a staple crop. Nevertheless, the impact of drought on common bean for both yield and nutrient concentration has not yet been concurrently investigated in a field environment. Using 10 bred lines developed by CIAT and its partners for their improved adaptation to drought and phosphorus deficiency, this study characterised the impact of drought on yield and nutrient concentration for leaf and seed tissue of common bean grown in the field. Drought significantly reduced leaf area (by ~50%), harvest index (by ~60%), yield (by ~70%), seed weight (by ~25%) and enriched carbon isotope abundance (δ13C) in the seed. Within the soluble leaf fraction, drought significantly decreased the concentration of mineral nutrients and amino acids, whereas no negative effect on the concentration of nutrients and amino acids was detected within the seed. Genotypic variation in nutrient concentration in both the leaf and seed tissue was identified and should be explored further to identify traits that may confer tolerance to abiotic stress. [ABSTRACT FROM AUTHOR]