Physiological traits associated with recent advances in yield of Chinese wheat

China represents around 20% of world population and this proportion will remain similar in the coming decades, whereas an improvement in diet will increase the consumption of wheat. Although wheat grain yields have been increasing in the last three decades, the challenges of feeding nearly 1.4 billion people will be significant in the next few decades. To satisfy this demand, it is paramount to study what agronomical and physiological traits may contribute to higher yield potential in wheat. Towards this goal, wheats from Henan Province, which is one of the wheat baskets of China, have been studied in this thesis. The objectives of this study were to identify the combination of agronomical, morphological and physiological traits that have contributed to the substantial improvements in yield potential of recently released Chinese winter wheats and to test phenotypical approaches that may help to speed further breeding advances in Chinese wheats. The yield potential of modern Chinese genotypes has grown as a result of an increase in harvest index (HI), grain number per unit area, and total above-ground biomass, whereas thousand kernel weight has been less affected. By contrast, most of the high yield genotypes are moderately adapted to stress conditions and highly susceptible to yellow rust strains in high-yielding Mediterranean conditions, indicating that stress adaptation has not been a priority in recent Chinese breeding for yield potential conditions. The stress adapted “ ideotype” consists of taller plants with a higher green aerial biomass, particularly during the reproductive stage, together with a better water status, the capacity to take up water during grain filling and a higher nitrogen use efficiency that is related to a more efficient uptake and utilization of N fertilizer. Moreover, the net photosynthesis (Pn) and stomatal conductance (gs) in flag leaves do not appear to be related to increases in yield potential, while total CO2 fixed by the whole ear appears to have a clear role in the yield increase. Studies of carbon (? 13C) and oxygen (? 18O) isotope composition have suggested that higher water use efficiency is involved in raising yield potential. However, such an increase was not achieved through a decrease in gs. By contrast, the high yield potential genotypes have higher nitrogen use efficiency (NUE), N remobilization capacity and uptake capacity during grain filling. These improvements were achieved by optimizing the ear N source/sink balance, which is mainly the result of N released from Rubisco degradation during grain filling. Besides detecting the physiological traits contributing to raising yield potential, testing for effective phenotyping tools to assess stress tolerance is important in breeding. This is the case for biotic stresses, such as yellow rust, where the use of low cost phenotyping approaches may help to select rust tolerance in the breeding pipeline. The use of conventional (i.e. red/blue/green, RBG) images provided an affordable approach to detect genotypic tolerance to yellow rust. Some colour characteristics, including hue, green fraction, greener fraction, a, and u have proved to be more efficient than other more conventional phenotyping approaches.