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 condi tions. Two sets of 22 genotypes were used. One was developed for semi-humid environments (TA-genotypes) and was cultivated in 22 trials around the Med iterranean basin with a mean yield across genotypes and environments of 492 5 kg/ha. The other set was developed for drier conditions (CA-genotypes) an d was cultivated in 15 trials, with a mean yield of 3501 kg/ha. Morphophysi ological traits for each set were evaluated in 2 trials with contrasting wa ter regimes conducted in north-eastern Spain: Lleida-rainfed (LR) and Lleid a-irrigation (LI). Two kinds of traits were evaluated: developmental traits , including early vigour, plant height, and phenology (days from planting t o heading and to maturity); and traits related to photosynthetic performanc e 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 th e mean yield of the same genotypes across all the sites where they were cul tivated. Yield measured at either of the 2 environments at Lleida was a muc h poorer predictor of genotype differences in mean yield than most of the t raits. Nevertheless, the kind of environment where the morphophysiological traits were evaluated affected the performance of these traits as yield pre dictors. The combination of significant traits measured in the better envir onment (LI) explained 71% and 55% of genotype variability in yield within T A- and CA-genotypes, respectively, but only 56% and 27% when they were eval uated at LR. On the other hand, growing conditions of the yield trials was the main factor determining the best combination of traits. For TA- genotyp es, larger yields were associated with shorter plants and higher carbon iso tope discrimination (Delta) of grains, and to a lesser extent with higher e arly vigour and lower canopy temperature, whereas phenological traits made no contribution to explaining genotype differences in yield. For the CA-gen otypes, higher yields were related to an earlier heading date or alternativ ely to a higher chlorophyll content during grain filling. A higher Delta in mature kernels also seems to be a positive trait.