Comparative performance of delta C-13, delta O-18 and delta N-15 for phenotyping durum wheat adaptation to a dryland environment

Grain yield and the natural abundance of the stable isotope compositions of carbon (delta C-13), oxygen (delta O-18) and nitrogen (delta N-15) of mature kernels were measured during 3 consecutive years in 10 durum wheat genotypes (five landraces and five modern cultivars) subjected to different water and N availabilities in a Mediterranean location and encompassing a total of 12 trials. Water limitation was the main environmental factor affecting yield, delta C-13 and delta O-18, whereas N fertilisation had a major effect on delta N-15. The genotypic effect was significant for yield, yield components, delta C-13, delta O-18 and delta N-15. Landraces exhibited a higher delta C-13 and delta N-15 than cultivars. Phenotypic correlations of delta C-13 and delta O-18 with grain yield were negative, suggesting that genotypes able to sustain a higher water use and stomatal conductance were the most productive and best adapted; delta N-15 was also negatively correlated with grain yield regardless of the growing conditions. delta C-13 was the best isotopic trait in terms of genetic correlation with yield and heritability, whereas delta O-18 was the worst of the three isotopic abundances. The physiological basis for the different performance of the three isotopes explaining the genotypic variability in yield is discussed.