Effect of Progressive Drought On Yield, Root Carbohydrates and Amino Acids Composition of Different Alfalfa Accessions.

Water deficit is a major environmental factor limiting crop production in arid and semi-arid regions of the world. The effect of water deficit cycles on shoot and root biomass yield, root carbohydrates and amino acids of different alfalfa accessions (Medicago sativa L.) varying in water use efficiency and yield potential, were studied near Las Cruces, NM in 2006 and 2007. Shoot biomass of well-watered or baseline (100 % irrigation) and water deficit or stress 1 & 2 in successive growth cycles (50 % irrigation) was harvested from non-stressed and visibly wilting plants, respectively. Root biomass yield was collected at the end of 2007. Water deficit reduced shoot biomass yield between 65 to 80 % regardless of alfalfa accessions compared to well-watered alfalfa in both years. Wilson had highest shoot and root biomass, while Falcata and MFC 192 had lowest shoot and root biomass in either year, indicating that drought tolerance may be conferred to plants with extensive deep root system. Accumulation of different levels of storage carbohydrates and amino acids in roots is associated with osmotic adjustment and positive turgor maintenance that helps in drought survival. Identification of alfalfa accessions with high water use efficiency, good root architecture and extensivity, high root carbohydrate and amino acid reserves also helps to select and breed alfalfa suitable for environments with limited water availability. Results from root carbohydrate and amino acid analysis will be presented to reveal any osmoprotective role under drought.