A Rapid Colorimetric Method for Epicuticular Wax Contest of Sorghum Leaves¹

Abstract

Epicuticular wax deposition on sorghum [ (Sorghum bicolor ) L. Moench] leaf blades imparts drought resistance. Screening of a large number of sorghum genotypes for increased leaf epicuticular wax content, utilizing the available gravimetric method, is impractical. A more rapid colorimetric method was developed and evaluated against the current gravimetric method. The colorimetric method is based on the color change produced due to the reaction of wax with acidic K 2 Cr 2 O 7 reagent. Wax content determined by the colorimetric method was highly correlated (r = 0.984) with that determined by the gravimetric method. Leaf epicuticular wax content in 11 fieldgrown grain sorghum cultivars did not vary between growth stage #4 (tip of flag leaf showing) and #7 (soft dough), at which stages comparable wax readings were obtained among the four top leaf blades. A CK 60 ‘bloomless’ (bmbm) genotype had only half of the epicuticular wax content of the CK 60 ‘normal’ (BmBm) genotype. Ten cultivars, all of the BmBm genotype, significantly differed in epiculticular wax content, ranging from 1.14 to 1.99 (SE = 0.006) mg/dm 2 of leaf.