Water Conservation and Stress Tolerance in the Phaseolus Genus.

Affecting over 60% of the dry bean production worldwide, drought is a worldwide constraint to bean (Phaseolus) production. Given the well-known caloric, nutritional and cultural significance of dry beans, understanding plant behavior that leads to drought avoidance or water conservation is a matter of priority. Improvements in bean drought resistance has been limited not only by focusing on just yield as a drought indicator, but also by the complexity of the traits involved and its poorly understood genetic basis.  There has been little to no research focusing on variations of stomatal conductance, transpiration or similar physiological responses as a way to improve water conservation and drought avoidance in beans. Our investigation aimed at exploring such physiological responses as a way to better direct integrative bean breeding efforts for drought tolerance. By selecting fifty genotypes from three different species of Phaseolus and growing them in pots in the field, we were able to see great variability in the response mechanism to the imposed drought treatment. Within these fifty are the parents of a multiparental inbred line (MAGIC) population created to recombine diversity within the Mesoamerican gene pool. In order to normalize for the expected variability in growth patterns, each of the genotypes of interest were grown in pots in companion with a reference genotype, Tio Canela, whose response to drought has been very well documented. Differences were seen in photosynthetic rates, stomatal conductance and biomass accumulation. The data collected allowed us to quantify and rank the physiological variation present in terms of soil water deficit stress response and tolerance of the different Phaseolus sp. and the 50 genotypes selected. A transpiration experiment carried alongside the stress tolerance experiment allowed us to evaluate if conservative water use in plants had a tradeoff with stress tolerance across the diversity of bean germplasm.