Assessing and Comparing Relationships Between Heat and Drought Tolerance: Analytical Approaches

Drought and heat tolerance are expected to become increasingly important considerations in agriculture and plant breeding.  Identifying promising sources of heat and drought tolerant genetic materials will be crucial to efforts to develop adaptable varieties that can perform when stressed.    However, heat stress exacerbates drought stress, and drought affects heat tolerance with consequent effects on identification and utilization of elite germplasm in breeding programs.  This is particularly important for common bean, not only because it is the most widely human consumed legume, but also because of its importance as a protein source in the developing world where heat and drought stresses are common.  Accordingly, we have been testing both new as well as conventional advanced technologies to assess their applicability to identifying the separate and combined effects of heat and drought on diverse bean genotypes.  Our goal is to develop a rapid and efficient phenotyping method for evaluating stress resistance in fields, greenhouses, and growth chambers.  The expectation is that other researchers may then use this method in their own germplasm evaluations; while such methods can never replace field evaluations, they can act as a supplement to field data by providing information on how varieties perform in conditions that are difficult to reliably replicate in the field.  A variety's field performance could be used to characterize its response to stress for the traits measured, and we could use that information to discover any trends among stress tolerant or stress susceptible varieties. For our experiments, we selected several advanced bean lines with known performance in the field. To date, our results show clear differences in the germplasm that we tested for traits measured under elevated temperatures.  These traits included photosynthetic rates, stomatal conductance, leaf temperature, and plant survival, and chlorophyll fluorescence traits such as photosystem II efficiency, non-photochemical quenching, and linear electron flow.  Additionally, a number of these traits showed clear correlations with each other.  From these results a simple, replicable screening method for heat stress tolerance emerges that researchers can readily adapt to the equipment on hand and from which they can infer a variety's drought tolerance.