Identification Of Physiological And Morphological Traits Governing High Water Use Efficiency In Alfalfa

To sustain high production of alfalfa (Medicago sativa) with limited water resource in many areas, cultivars with improved water use efficiency (WUE) are urgently needed. We recently conducted greenhouse experiments and identified an alfalfa collection, River side (RS) that is naturized to the environment in the Grand River National Grassland in South Dakota, with a greater water use efficiency (WUE) under drought than other ten alfalfa accessions. To understand the mechanisms that may contribute to the higher WUE in RS, we examined physiological and morphological traits in comparison with Alfagraze (AF), a commercial variety with lower WUE under drought under greenhouse conditions. RS showed a greater reduction of water loss through transpiration despite more stomata per unit area under drought. Both RS and AF showed a reduction of stomatal aperture under drought compared to respective well-watered plants but stomatal aperture in RS was smaller compared to AF regardless of irrigation status. Leaves of RS showed a more rapid accumulation of abscisic acid (ABA), at 14 days versus at 28 days in AF under drought. RS also closed stomata more rapidly when treated with 10 mu M ABA. In addition, leaves of RS showed denser but shorter leaf hairs under drought. A correlation analysis points to a greater stomatal sensitivity to ABA in RS as a key factor contributing to its greater WUE under drought.