Physiological Basis for Improving Yield and Water Use Efficiency of Wheat in the Southern High Plains.

Soil water deficit is a primary factor limiting wheat yields in the US Southern High Plains, and improving crop water uptake and water use efficiency (WUE) has been the major focus in the region. Selection of cultivars with more drought resistance is an important management strategy for improving yield and WUE under water-limited conditions. Two newly released Texas AgriLife Research cultivars, TAM 111 and TAM 112, are widely grown in the High Plains and are consistently among the highest yielding cultivars under water-limited conditions across the region. However, the underlying physiological mechanisms for improved yield and WUE in these cultivars are not well understood. The objective of this study is to investigate the physiological determinations of yield and WUE in these two widely grown wheat cultivars. The two cultivars along with two cultivars released earlier (TAM 105 and TAM 110) were grown under two soil water regimes (dryland and irrigated) during the 2009-10 season at Bushland, TX. Field measurements include profile soil water content, canopy temperature depression (CTD), gas exchange, biomass at anthesis and maturity, and yield components.  In both dryland and irrigated plots, TAM 111 and TAM 112 yield 10% more than TAM 110 and 20% more than TAM 105.  The higher yield in newer cultivars is a result of more seeds per spike and heavier seeds. Compared to TAM 105, TAM 111 and TAM 112 consistently have higher spike and stem dry weight at anthesis, indicating the newer cultivars have larger sink size.  In addition, remobilization of carbon reserves from stems contributes to yield under dryland conditions.  The initial gas exchange and CTD data showed that TAM 111 and TAM 112 may have different mechanisms to respond drought stress.