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  1. Vol. 33 No. 1, p. 178-186
     
    Received: Dec 23, 1991
    Published: Jan, 1993


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doi:10.2135/cropsci1993.0011183X003300010032x

Gas Exchange, Carbon Isotope Discrimination, and Productivity in Winter Wheat

  1. Jack A. Morgan ,
  2. Daniel R. LeCain,
  3. Thomas N. McCaig and
  4. James S. Quick
  1. R es. Stn. Branch, Agric. Canada, Swift Current, SK S9H 3X2, Canada
    Q uick, Agronomy Dep., Colorado State Univ., Ft. Collins, CO 80525

Abstract

Abstract

Leaf gas exchange theory indicates that carbon isotope discrimination (∆) is negatively associated with CER/g3 (leaf CO2 exchange rate/conductance). Discovery of genetic variation for ∆ in wheat (Triticum aestivum L.) and other species has generated interest in using carbon isotope discrimination in plant breeding. However, the hypothesized negative association between CER/g3 and & has sometimes not been observed in field-grown crops. In the present study, CER/g3, & of peduncle tissue, plant productivity and yield were examined in eight winter wheat genotypes under both irrigated and nonirrigated field conditions. Water stress- and genotype-induced variations in CER/g3 were more consistently correlated with variations in gs than with CER. However, low CER in ‘Bezostaya’ wheat resulted in a consistently low genotypic ranking for CER/g3. In 1988, values of CER/g3 increased with water stress, while ∆ values dropped from 18.17 to 17.48‰. These results imply a negative relationship between CER/g3 and ∆, consistent with leaf gas exchange theory; however, ∆ was both positively (1988; r = 0.83** [P ≤ 0.01]) and negatively (1989; r = -0.79* [P ≤ 0.05]) associated with CER/g3 in irrigated plots. Positive correlations were obtained between ∆ and both biomass productivity (1988, r = 0.54*; 1989, r = 0.45 [P = 0.08]) and grain yield (1988, r = 0.66*; 1989, r = 0.55*) when data were averaged across genotypes and irrigation treatments. Consistently low ∆ values were obtained for ‘Sturdy’, an early-released, drought-susceptible cultivar with low productivity. These results suggest that genotypic rankings for peduncle ∆ must be carefully interpreted, as low ∆ can be associated with low yield and stress susceptibility in wheat.

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