The Influence of Leaf Epicuticular Wax On Stomatal Conductance, Canopy Temperature, and Chlorophyll Content in Long-Term High Temperature Stressed Spring Wheat (Triticum aestivum).

Leaf epicuticular wax (EW) acts as a barrier between leaf tissue and the surrounding environment. EW protects the leaf from fungal attacks, moisture loss from stomates as well as excess heat, and radiation. Preliminary tests have identified the influence of EW in decreasing heat susceptible index (HSI), leaf canopy temperature (CT), and improving total wheat (Triticum aestivum) yields. Most cultivars show the presence of leaf EW, but its role in improving high temperature stress tolerance during reproductive stages has yet to be defined. This study seeks to provide insight to the behavior of flag leaf EW during different reproductive stages of spring wheat cultivars. Seven spring wheat cultivars were studied in the green house exposed to high temperature treatment (21⁰C-night and 38⁰С-day) during 2013. Leaf EW discs and physiological data (stomatal conductance-SC, chlorophyll fluorescence (CF), leaf CT) were collected every 3 days after head initiation to 15 days after pollination (DAP). Results showed a significant increase in EW load on the flag leaf surface from head initiation to 15 DAP. CF remained constant from 10 DAP to 15 DAP, suggesting that chlorophyll content was not much significantly decreased. SC was significantly lower at 10 DAP compared to 3 DAP and 15 DAP. The cultivar ‘Seri M82’ ‘Len’ and ‘Halberd’ exhibited high levels of leaf EW and low adaxial SC under high temperature treatment. Leaf adaxial surface had significantly higher SC compared to abaxial surface. Leaf epicuticular wax of Seri M82 showed a strong or significant correlation with CT (-49%), leaf temperature depression (43%), SC-abaxial (-27%), and CF (71%). Leaf EW significantly influences SC, CF, and leaf CT during reproductive stages.