Contrasting Phaseolus crop water use patterns and stomatal dynamics in response to terminal drought

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

Crop biotechnology for improving drought tolerance : targets, approaches, and outcomes

Human population growth and climate change threaten our food and water security. The increasing frequency of extreme drought events will cause major crop yield losses. To mitigate this threat to global food security, we need to rapidly select and/or develop new ‘climate‐ready’ crop varieties that can withstand and flourish under water deficit, enabling the sustained and sustainable production of higher yields to support human life on Earth. In this article, we identify the current targets for crop plant improvement under drought, working from the ground up, with modifications in rooting, shoot, stomatal, and photosynthetic systems, and finally nutrient transport and sink strength. We argue that by using a holistic approach to crop development, prudently incorporating the natural variation available in crop wild relatives and cultivars with cutting‐edge tools, such as molecular breeding and transgenics, we may be able to produce high‐yielding crops under a range of conditions to meet our needs in a changing world