Agronomic and physiological traits associated with breeding advances of wheat under high-productive Mediterranean conditions. The case of Chile

Wheat yields in Chile have increased significantly during the last four decades as a consequence of plant improvement and better crop husbandry. Central Chile is characterised by high-yield Mediterranean conditions, where precipitation received by the crop in most years does not represent a major limitation to productivity. This study assesses the changes in agronomic and physiological traits of spring cultivars released in the country between 1920 and 2000. A total of 95 spring bread wheat accessions, representing 20 old and 75 modern cultivars (released before and after 1960, respectively) were tested in a humid Mediterranean-type climate, with irrigation. Modern genotypes exhibited higher grain yield, harvest index, number of grains per ear and sedimentation values and lower height, test weight, wet gluten content and hardness index. No differences were found for days to heading, and ear length, whereas kernel weight decreased with the Green Revolution. Principal component (PC) analysis using ten agronomic traits clearly separated modern from old cultivars. Grain yield, a trait not included in PC analysis, was highly correlated with the first PC (r= 0.80, P < 0.0001), where modern cultivars presented lower plant height, higher harvest index and better grain quality, as indicated by the higher sedimentation values and lower hardness index values. The year of release of cultivars was related negatively to plant height and positively to harvest index, number of grains per ear and sedimentation value. In a further study, changes in photosynthetic and transpirative traits were investigated in a subset of 14 genotypes covering the same 80-year range. Differences in grain yield across genotypes were related positively to stomatal conductance and transpiration rates of the flag leaves during grain filling and negatively to oxygen isotope composition and (to a lesser extent) carbon isotope composition in kernels. The results suggest that the higher grain yield of modern varieties is related to higher stomatal conductance and transpiration. (C) 2013 Elsevier B.V. All rights reserved.