Comparative performance of the stable isotope signatures of carbon, nitrogen and oxygen in assessing early vigour and grain yield in durum wheat

The present paper studied the performance of the stable isotope signatures of carbon (δ¹³C), nitrogen (δ¹⁵N) and oxygen (δ¹⁸O) in plants when used to assess early vigour and grain yield (GY) in durum wheat growing under mild and moderate Mediterranean stress conditions. A collection of 114 recombinant inbred lines was grown under rainfed (RF) and supplementary irrigation (IR) conditions. Broad sense heritabilities (H²) for GY and harvest index (HI) were higher under RF conditions than under IR. Broad sense heritabilities for δ¹³C were always above 0·60, regardless of the plant part studied, with similar values for IR and RF trials. Some of the largest genetic correlations with GY were those shown by the δ¹³C content of the flag leaf blade and mature grains. Under both water treatments, mature grains showed the highest negative correlations between δ¹³C and GY across genotypes. Flag leaf δ¹³C was negatively correlated with GY only under RF conditions. The δ¹³C in seedlings was negatively correlated, under IR conditions only, with GY but also with early vigour. The sources of variation in early vigour were studied by stepwise analysis using the stable isotope signatures measured in seedlings. The δ¹³C was able to explain almost 0·20 of this variation under RF, but up to 0·30 under IR. In addition, nitrogen concentration in seedlings accounted for another 0·05 of variation, increasing the amount explained to 0·35. The sources of variation in GY were also studied through stable isotope signatures and biomass of different plant parts: δ¹³C was always the first parameter to appear in the models for both water conditions, explaining c. 0·20 of the variation. The second parameter (δ¹⁵N or N concentration of grain, or biomass at maturity) depended on the water conditions and the plant tissue being analysed. Oxygen isotope composition (δ¹⁸O) was only able to explain a small amount of the variation in GY. In this regard, despite the known and previously described value of δ¹³C as a tool in breeding, δ¹⁵N is confirmed as an additional tool in the present study. Oxygen isotope composition does not seem to offer any potential, at least under the conditions of the present study.