Photosynthetic and developmental traits associated with genotypic differences in durum wheat yield across the Mediterranean basin.

The relationships between various morphophysiological traits and yield were studied in durum wheat (Triticum durum Desf.) grown in Mediterranean conditions. Two sets of 22 genotypes were used. One was developed for semi-humid environments (TA-genotypes) and was cultivated in 22 trials around the Mediterranean basin with a mean yield across genotypes and environments of 4925 kg/ha. The other set was developed for drier conditions (CA-genotypes) and was cultivated in 15 trials, with a mean yield of 3501 kg/ha. Morphophysiological traits for each set were evaluated in 2 trials with contrasting water regimes conducted in north-eastern Spain: Lleida-rainfed (LR) and Lleida-irrigation (LI). Two kinds of traits were evaluated: developmental traits, including early vigour, plant height, and phenology (days from planting to heading and to maturity); and traits related to photosynthetic performance such as canopy temperature and chlorophyll content of the flag leaf, both measured during grain filling, and carbon isotope discrimination of mature grains. All the traits, measured in both Lleida trials, were related to the mean yield of the same genotypes across all the sites where they were cultivated. Yield measured at either of the 2 environments at Lleida was a much poorer predictor of genotype differences in mean yield than most of the traits. Nevertheless, the kind of environment where the morphophysiological traits were evaluated affected the performance of these traits as yield predictors. The combination of significant traits measured in the better environment (LI) explained 71% and 55% of genotype variability in yield within TA- and CA-genotypes, respectively, but only 56% and 27% when they were evaluated at LR. On the other hand, growing conditions of the yield trials was the main factor determining the best combination of traits. For TA-genotypes, larger yields were associated with shorter plants and higher carbon isotope discrimination (Δ) of grains, and to a lesser extent with higher early vigour and lower canopy temperature, whereas phenological traits made no contribution to explaining genotype differences in yield. For the CA-genotypes, higher yields were related to an earlier heading date or alternatively to a higher chlorophyll content during grain filling. A higher Δ in mature kernels also seems to be a positive trait.