Carbon isotope discrimination and indirect selection for transpiration efficiency at flowering in lentil (Lens culinaris Medikus), spring bread wheat (Triticum aestivum L.) durum wheat (T. turgidum L.), and canola (Brassica napus L.)

Summary Carbon isotope discrimination has been proposed to indirectly select for transpiration efficiency in several C₃ species. To determine the effectiveness of carbon isotope discrimination to indirectly select for transpiration efficiency at flowering we measured: (i) variability for carbon isotope discrimination, (ii) the magnitude of the genotype-by-water regime interaction for carbon isotope discrimination, and (iii) the magnitude of the correlation between carbon isotope discrimination and both transpiration efficiency and dry matter at flowering. Ten lentil (Lens culinaris Medikus) genotypes, ten wheat genotypes (eight spring wheat (Triticum aestivum L.) and two durum wheat (Triticum turgidum L.)), and ten canola (Brassica napus L.) genotypes were grown in a greenhouse at 80, 50 and 30% field capacity. Above ground dry matter was harvested at 80% flowering and dry matter at flowering, water used, and carbon isotope discrimination determined. Genotype variation for carbon isotope discrimination was observed in lentil, spring wheat and canola at each water regime, and when averaged over the three water regimes. The largest range in carbon isotope discrimination among lentil and spring wheat genotypes was observed using the wet regime; whereas, the dry regime provided the largest range for CID in canola genotypes. In all species the genotype-by-water regime interaction for carbon isotope discrimination was nonsignificant. The correlation between carbon isotope discrimination and dry matter at flowering was inconsistent across water regimes and years. In addition, in all three crops, no correlation was observed between carbon isotope discrimination and transpiration efficiency at any of the water regimes, and when averaged over water regimes and years. These results suggests that under the conditions reported here, carbon isotope discrimination cannot be used effectively to indirectly select for transpiration efficiency in lentil, spring wheat, and canola.Abbreviations CID carbon isotope discrimination - DMF dry matter at flowering