Screening of Spring and Winter Wheat for Water Use Efficiency by Carbon Isotope Discrimination Analysis.

Breeding for drought tolerance through selection for yield is complicated due to the higher influence of environmental factors. An alternative is to select for individual physiological traits that are less influenced by the environment. Carbon isotope discrimination (CID) is a potentially valuable physiological technique for indirect selection of water use efficiency (WUE) of wheat because of the high heritability of CID values. To determine the relationship between CID and wheat variety performance under terminal drought stress conditions in the Pacific Northwest (PNW), Washington State University’s soft and hard spring wheat variety trials located at Pullman (>50 cm annual rainfall, n=40, 2009) and Connell (<30cm rainfall, n=48, 2010), WA, and soft and hard winter wheat variety trials located at Lind (<30cm rainfall, n=90 in 2010 and 2011), WA, were screened. All genotypes were planted in an alpha lattice design with three replications. Flag leaves were sampled when boots started to swell or ¼ of inflorescence started to be visible. Leaf samples were dried at 80^oC for 48 hrs, finely ground and analyzed by mass spectrometry. The agronomy and phenological traits including yield, test weight, protein, plant height and heading measured in all rainfall regions (<30cm to >50cm rainfall) on spring and winter wheat, were used to correlate with CID. The CID values have shown good correlations with yield, test weight, protein and plant height. So far low CID values (high WUE) have been correlated with yield and test weight in spring wheat but not in winter wheat.