Water Stress and Genotypic Effects on Epicuticular Wax Production of Alfalfa and Crested Wheatgrass in Relation to Yield and Excised Leaf Water Loss Rate

Epicuticular wax production has been found to be associated with higher seed yield of drought-stressed crops. The present study was conducted to determine the relationship between epicuticular wax and forage yield in two range plant species. A line-source sprinkler system under an automated rainout shelter imposed an irrigation water gradient on 30 clones of alfalfa (Medicago sativa L.) from two source populations and 30 clones of crested wheatgrass (Agropyron desertorum [Fisch. ex Link] Schult.). Leaf epicuticular wax was determined gravimetrically at three contrasting water levels. Epicuticular wax production increased for all clones as water application declined in all three harvests for alfalfa and in the first harvest for crested wheatgrass. At the low water level, clones of creeping-rooted Spredor 2 alfalfa produced more epicuticular wax per unit leaf area than noncreeping-rooted NC-83-1 clones. Within the three water levels, epicuticular wax production and yield were not correlated in alfalfa for any harvest. Yield and epicuticular wax were negatively correlated at the medium and low water levels for crested wheatgrass at Harvest 1 and positively correlated at the high water level for Harvest 2 (aftermath). No consistent relationship was found between epicuticular wax production and cuticular transpiration as estimated by water loss rate of excised leaves of alfalfa and crested wheatgrass.