EPICUTICULAR WAX LOAD OF NEAR-ISOGENIC BARLEY LINES DIFFERING IN GLAUCOUSNESS

Scanning electron microscopy observations of epicuticular waxes on flag leaves (blades and sheaths) and ears were carried out on a pair of near-isogenic lines of two-row barley (Hordeum vulgare L.), derived from cv. Troubadour, differing in their degree of glaucousness (wax bloom). Plants were grown under irrigated and rainfed mediterranean conditions. Wax bloom in flag leaves consisted mainly of thin wax deposits over the blade, and tubes over the sheath. Wax bloom in the blade was denser and more uniformly arranged on the adaxial than on the abaxial side. In the ears, tubular waxes predominated, forming dense patches on awns and lemmas, and becoming sparse on inner bracts such as the palea. Wax bloom increased under rainfed conditions in both lines. There were marked differences between the lines in the extent of deposition of crystallized epicuticular waxes in the leaf sheath and the ear, whereas differences in the leaf blade were less evident. Wax bloom was almost absent on the sheaths and ear of the non-glaucous line. These results suggest separate genetic control of epicuticular wax deposition on different parts of barley plants. The role of wax bloom in two related ecophysiological parameters, canopy reflectance and cuticular conductance to water diffusion, was also studied. Reflectance by the canopy in the 400 to 700 nm wavelengths was over 50% higher in the glaucous than in the non-glaucous line under rainfed conditions. Under irrigated conditions, flag leaf blades of the non-glaucous line showed the highest epidermal conductance. Ears showed no clear differences in epidermal conductance between lines or growth conditions.