Maximum Transpiration Rate to Improve Crop Water Use for Water Limited Environments.

Simulation studies have shown that in most years in the U.S. water deficits develop that result in yield loss.  It was hypothesized that yields might be increased by having crop plants that express a maximum transpiration rate so that under high vapor pressure deficit conditions crop water loss is restricted to the maximum rate.  A phenotypic expression of this trait would be partial stomata closure during midday when vapor pressure deficit is high.  While the negative aspect of this trait would be a loss in CO2 accumulation during periods of decreased stomatal conductance, water conservation early in the growing season as a result of this trait would save soil water to support crop physiological activity during grain fill.  In fact, simulation studies showed that in many environments yields would be increased as a result of this trait.  Germplasm expressing the maximum-transpiration trait has now been identified in most major grain crops.  The trait has been tracked to limiting plant hydraulic conductance, which is associated with differences in the aquaporin populations of the maximum-transpiration germplasm.