Cuticular wax variants in a population of switchgrass (Panicum virgatum L.)

Leaf cuticular waxes are known to influence both biotic and abiotic stress tolerances of plants. The objective of this work was to characterize the wax phenotypic diversity present in a population of 1849 switchgrass plants. We identified 92 visually distinct variant plants that possessed altered leaf glaucousness relative to the common standard type (ST), which exhibited a bluish-white (glaucous) leaf color. The variants could be grouped into three classes: 1) non-glaucous types (NG) that possessed a shiny green leaf surface, 2) reduced glaucous types (RG) that appeared less glaucous than ST, and 3) highly glaucous types (HG) that exhibited more intense bluish white color than ST. Analyses of total cuticular wax content averaged over each of three NG (mean 304.79 +/- 15.16 mu g/dm(2)), RG (mean 533.33 +/- 21.62 mu g/dm(2)) and HG types (mean 1228.23 +/- 45.74 mu g/dm(2)) showed significant differences (P < 0.001) from three selected STs (mean 810.92 +/- 30.57 mu g/dm(2)). Analysis of wax composition among these selected types revealed that the C-33 beta-diketones were the most abundant wax compounds in all but NG types. Field emission scanning electron microscopy showed that abaxial leaf surfaces exhibited predominantly rod-shaped crystals, and adaxial surfaces exhibited predominantly plate-shaped wax crystals on all lines, except for NG that lacked wax crystals on the abaxial leaf surface. As a target for crop improvement, this study reveals that a large amount of variation for cuticle waxes exists within this switchgrass germplasm.