Leaf Epicuticular Wax Deposition Study and Mapping Waxy QTL for Wheat Drought Lines.

Leaf Epicuticular Wax Deposition Study and Mapping Waxy QTL for Wheat Drought Lines Suheb Mohammed, Trevis Huggins, Francis Beecher, Christopher Chick, Ashima Paudel, and Dirk B. Hays Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843 Growing wheat in environments with little rainfall is a challenging task. Epicuticular wax is one of several physiological traits important during drought tolerance due to its relationship with decreased water loss from the leaf’s surface. The deposition of long chain n-alkanes on the leaf surface is a complex process. We hypothesized that since wax deposition likely increases in rate from flower initiation through the grain filling stage an overlap should exist between QTL’s for drought tolerance and wax deposition. To test our hypothesis an Australian cultivar, Halberd, with high levels of waxy on the flag leaves was crossed with the US cultivar, Len with limited leaf wax to develop a population of 183 recombinant inbred lines to map drought tolerance associated QTL’s. An underground drip irrigation system was utilized. RIL’s segregating for wax were grown at 3 locations College Station (39.6 inches), Uvalde (23 inches), and Chilicothe (36 inches) Texas. Drought was imposed by decreasing water application from stem initiation through grain formation in a block of 2 replications of each RIL versus a separate control block of 2 replications that received continued watering to maturation. Leaf wax samples were collected at 10DAP in field. In a separate study, leaf samples from the parental lines grown in the greenhouse were collected at 5DAP, 10DAP, 15DAP, 20DAP, 25DAP, and 30DAP determine the variation in wax deposition during development. Day/night temperature was maintained at 25 ?C for drought and control. Heat treated plants at 10DAP, were shifted to a high temperature greenhouse where day/night temperature was maintained at 25/35 ?C. Leaf temperature and stomatal conductance was measured and leaf wax samples were collected between mid-day 12 and 2 PM. Wax samples were extracted using chloroform and analyzed through GC/MS or a colorimetric assay. We expect leaf temperature and stomatal conductance to significantly correlate with leaf wax deposition from 5DAP to 30DAP respectively. Composite interval mapping Hal*Len RIL’s, which segregates for wax deposition and yield stability will allow us to identify QTLs regulating wax deposition and their overlap with yield stability under drought stress.