Do epicuticular waxes contribute to drought tolerance in sorghum (Sorghum bicolor L. Moench)? (with 3 tables & 3 figures)

High concentrations of leaf epicuticular waxes (LEW) are thought to enhance drought tolerance in plants because of a reduction in leaf temperature and reduced water vapor loss from 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 LEW load on leaf temperature, stomatal conductance, transpiration, and total water potential 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. Plants were grown in the field in northeastern Mexico near Ciudad Victoria, Tamaulipas, under both well-watered and water-stressed conditions and sampled at 42, 58, 73, and 89 days after planting. Leaf temperature was not affected by the amount of LEW and on average the leaf temperature was about 4 C higher under drought conditions than under irrigation. No correlation was found between the amount of LEW and stomatal conductance or transpiration. It was also found that soil water potential as controlled by watering regime did not correlate with LEW concentration. We conclude that higher LEW loads on the genotypes tested did not result in water conservation and did not appear to confer adaptive value to plants under drought conditions.