The Role of Leaf Epicuticular Wax in Improved Adaptation to Drought Stress.

Water deficiency is the primary reason for decreasing wheat (Triticum aestivum) yields globally, causing a nearly 50-90% yield reduction on at least 60 million hectare of land in developing countries (Reynolds et al., 2004). Previous studies have identified associations in genomic regions for cooler canopies, heat susceptible index, and grain yield components in winter wheat. This project aim is to define the role that leaf epicuticular wax (EW) plays as a drought adaptive trait in terms of yield stability. A spring wheat Len/Halberd recombinant inbred line population was used to test this question. The RIL population exhibits significant segregation for leaf EW, canopy temperature (CT), awns, and height yet has been selected to be uniform for flowering time (5-8 days difference. An alpha lattice design with 180 recombinants and 2 replications was used with two independent treatments at each location (water deficit and control conditions) at each of 5 environments over 3 years. The inheritance of leaf EW was low (12%) due to a high environmental influence. The RILs grown under water deficit produced significantly higher EW content (17 to 28%) compared to control. The leaf EW load significantly correlated with plot yield (32%), drought susceptibility index (DSI) (-30%), and leaf CT (-31%) under water deficit conditions. In addition, EW and CT correlated with higher yield stability using DSI and across environments using Eberhart stability during water deficit. Significant co-localized and stable QTLs for DSI of yield components, leaf EW, leaf CT, and yield components were identified on chromosomes 2B, 3B, 4A, 5B, 5A, 6A, 6B, 7A, and 7B. Colorimetric leaf EW QTL explaining a phenotype variation from 9 to 17% were identified across genome.  This study explains the inter relationship between leaf EW and cooler canopies in improving yield potential and stability under water deficit conditions in wheat. The co localized loci identified serve as potential target regions to screen for water deficiency tolerant lines in wheat germplasm and marker-assisted selection.