Environmental Physiology of Sorghum. II. Epicuticular Wax Load and Cuticular Transpiration1

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Abstract
The effect of epicuticular wax (EW) load on the cuticular transpiration rate (Tc of sorghum [Sorghum bicolor (L.) Moench] leaves was studied. Leaves from bloom, bloomless, and sparse bloom isogenic lines and various bloom‐type hybrids were collected from field plots after anthesis in 1976, 1977, and 1981. Epicuticular wax was extracted with chloroform and quantified using a colorimetric method. The Tc of detached leaves were measured with a humidity sensor in a closed cuvette or calculated from the mass of water lost per unit time under standardized conditions. The Tc increased as EW decreased over the range of 0.1 to 0.03 g m−2 when data from all genotypes were pooled for analysis. However, among the normal (bloom) phenotypes there was no clear association between rates of water loss and EW. These data suggest that EW greater than about 0.067 g m−2 provide an effective barrier to water loss through cuticles of sorghum leaves under most conditions. Although the two methods of measuring Tc produced the same qualitative results, Tc rates calculated from the mass of water transpired under more “realistic” controlled conditions were higher and probably more directly related to rates of water loss under field conditions. Because of its speed and technical simplicity, the water loss method appears superior when large numbers of samples must be evaluated.