High concentrations of leaf epicuticular waxes are thought to enhance water stress resistance in plants because of a reduction in leaf temperature and also reduced water vapor loss from the leaves. However, even though this phenomenon has been studied for some time, much remains to be understood about the relationship between leaf wax load and leaf responses under varied environmental conditions. In this study, we report the effects of leaf epicuticular wax load on leaf temperature (LT), stomatal conductance (g), transpiration (E), and total water potential (Psi) in four isogenic lines of sorghum (obtained from the sorghum research program at Purdue University, West Laffayette, Indiana), which varied with respect to epicuticular wax load. For this research, plants were grown in the field in northeastern Mexico (Ciudad Victoria, Tamaulipas), under both irrigated and non-irrigated conditions and sampled at 42, 58, 73, and 89 days after planting. Our results showed that LT was not affected by the amount of leaf epicuticular waxes and on average the LT was about 4 C higher under drought conditions than under irrigation. We found that g, E, and Psi were significantly correlated with leaf epicuticular wax load, but the degree of significance depended on sampling date. In general, we found that the isogenic lines with the greatest amounts of leaf epicuticular waxes showed the greatest reductions in g and E under non-irrigated conditions and also had the highest values for Psi. Under irrigated conditions, the effects of the leaf epicuticular waxes on the parameters measured were much reduced. In summary, we conclude from this study that under non-irrigated conditions, high epicuticular wax loads reduce water loss and hence allow the leaves to maintain a higher water potential.

Key words: epicuticular leaf wax, Sorghum bicolor, stomatal conductance, transpiration, water stress