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

Carbon isotope discrimination (CID) is a potentially valuable physiological technique for screening water use efficiency (WUE) of wheat because of the high heritability of the trait. To determine WUE through CID on Pacific Northwest (PNW) adapted wheat cultivars, 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, 2010 and 2011), WA, were screened. All genotypes were planted in alpha lattice design with three replications. Flag leaves were sampled at Zadok growth stage 45 and 53. Samples were dried at 80^oC for 48 hrs, finely ground and analyzed by mass spectrometry. High heritabilities and significant correlations (P<0.05) between CID values from different environments were found in soft spring (H²=0.89; r = 0.67) and soft (H² = 0.77; r = 0.55) and hard winter wheat (H² = 0.88; r = 0.73). No significant correlation was found between CID values of hard spring wheat. CID values were examined for correlations with multiple agronomical and phenological traits, including yield, test weight, protein, plant height and heading date. For the spring wheat, low CID (higher WUE) was significantly correlated (P<0.05) with higher yield (r = 0.51 to 0.70), test weight (r = 0.55 to 0.68) and protein (r = 0.47 to 0.49) in all rainfall regions. For the winter wheat, high CID (low WUE) was significantly correlated (P<0.05) with higher test weight (r = 0.48 to 0.64) and taller plants (r = 0.46 to 0.57), but was a poor indicator of yield in low rainfall environments. This indicates that, in the PNW wheat germplasm tested, low CID (high WUE) may be an important indicator of yield, test weight and protein in spring wheat but not in winter wheat.