Characterizing Water Use Efficiency (WUE) and Water Deficit Responses in Apple (Malus X domestica and Malus sieversii)

Reduced availability of water for agricultural use has been forecast for much of the planet, due in part to global warming which has contributed to numerous cycles of drought worldwide and due in part to greater urban demand for water in large metropolitan areas.  Strategic improvement of water use efficiency (WUE) and drought tolerance in perennial crops, like fruit trees, could reduce water use without compromising yield or quality. We studied water use in apple trees using ‘Royal Gala’, a relatively water use efficient cultivar, as a standard. To examine whether or not genes useful for improving WUE are represented in a wild relative genetically related to M. X domestica, we surveyed  Malus sieversii for traits associated with WUE and drought tolerance utilizing material collected from xeric sites in Kazakhstan. One such collection has been maintained at Geneva, NY and surveyed for various phenotypes, as well as simple sequence repeats (SSRs). These data suggest that most of the diversity in this population is contained within a subpopulation of 34 individuals. Our results indicate considerable diversity in this group with respect to WUE and transpiration, while other traits, such as leaf number and size, as well as stomatal size and density show little or no differences. These results imply that genetic diversity has resulted in changes in the biochemistry, uptake and/or transport of water, carbon or oxygen that have allowed these trees to survive in water-limited environments.