Chemical profiles of cuticular waxes on various organs of Sorghum bicolor and their antifungal activities

Sorghum bicolor is widely cultivated in arid and semi-arid areas. This paper reports the chemical profiles of cuticular waxes on adaxial and abaxial sides of common leaf, flag leaf, sheath and stem from six sorghum cultivars and the variations of leaf cuticular waxes at seedling, jointing and filling stages. Then, the bioassay of leaf and sheath wax were evaluated against Penicillium sp and Alternaria alternata. The six sorghum cultivars had similar wax profiles. In total, eight wax compounds were identified, including fatty acids, aldehydes, primary alcohols, alkanes, secondary alcohols, ketones, sterols and minor triterpenoids. Leaf wax coverage increased from 2.2 to 3.1 μg/cm² at seedling stages to 6.5-14.0 μg/cm² at jointing and filling stages, respectively. The relative abundance of primary alcohols decreased from 51 to 62% at seedling stage to 17-33% at jointing stage whereas alkanes increased from 5-9% to 19-33%. Leaf was dominated with alkanes (28.4%) and aldehydes (28.4%), sheath with acids (42.8%), and stem with aldehydes (80.8%). Epicuticular wax of leaf and sheath contained higher proportions of alkanes whereas the intracuticular waxes contained higher proportions of sterols. The leaf wax improved the growth of Penicillium but reduced that of A. alternaria, whereas sheath wax reduced the growth of Penicillium but unchanged A. alternaria. The detailed sorghum wax profiles improve our understanding of the physiological roles of these waxes and their diversified potential usages in industries.

Keywords: Antifungal effect; Crops; Epicuticular wax; Intracuticular wax; Sorghum.