Evolution Characteristics Of Grain Yield And Photosynthesis In Wheat Cultivars Form Different Eras

Field experiment were conducted using thirty-two winter wheat (Triticum aestivum ) cultivars released from 1950s to 1990s to investigate evaluation characteristics of grain yield and responses to nitrogen supply. Analyze the physiological mechanisms that lead to the differences in yield and photosynthetic capacity between the newer and older cultivars. Two nitrogen levels of 0 and 225 kg/hm~2 were implemented. The main results were as follows:There were significant differences in grain yield and yield components among thirty-two cultivars. The grain yield of the 1990s'cultivars were higher than those of old cultivars (1950s,1960s,1970s). Under lower nitrogen condition, 1000 kernels weight of wheat cultivars were higher than those of nitrogen application. Moreover, the 1990s'cultivars had higher NYE,NHI,NAE and NRE than old cultivars (1950s,1960s,1970s), but NPE was lower. The correlation analysis showed that grain yield were significantly positively correlated with NYE,NHI,NAE and NRE under nitrogen supply, which indicated wheat grain yield and nitrogen utilization efficiency were synchronously improved during wheat improvement process.There were significant differences in flag leaf photosynthetic characteristics in wheat cultivars form different eras. The results showed that chlorophyll content, net photosynthetic rate(P_n), PSII maximum photochemical efficiency (F_v/F_m), actual photochemical efficiency, photochemical quenching coefficient (qP), and the non-photochemical quenching coefficient (NPQ) for 1990s' cultivars were higher than those of old cultivars (1950s and 1970s) during grain filling. Furthermore, the diurnal changes of photosynthetic parameters for all cultivars were same, but photosynthetic and fluorescence parameters were higher for 1990s' cultivars than that for 1950s' and 1970's cultivars. For 1990s' cultivars, the activities of SOD and CAT and soluable protein content in flag leaves declined more slowly during late grain filling as compared with that for 1950s' and 1970's cultivars, while MDA content showed adverse trend. The results indicate that improved photosynthetic capacity and postponed senescenceprogress are key physiological reason for grain yield enhancement during wheat cultivars improvement.There were significant differences in the transport and accumulate of carbon in different wheat cultivars for different eras. The ability of pre-anthesis stored assimilate and post-anthesis assimilation for 1990s' cultivars were higher than those of old cultivars (1950s and 1970s) during grain filling. The 1990s'cultivars had higher total amount of pre-anthesis stored assimilate and post-anthesis assimilation than old cultivars (1950s,1960s,1970s). At the same time , the ability translocation of pre-anthesis stored nitrogen and post-anthesis assimilation nitrogen for 1990s' cultivars were higher than those of old cultivars (1950s and 1970s) during grain filling. The amount of nitrogen accumulation for 1990s' cultivars were higher than those of old cultivars (1950s and 1970s) during pre-anthesis. The 1990s'cultivars had higher nitrogen accumulation in leaf, and had lower nitrogen accumulation in else vegetative parts at anthesis. The 1990s' cultivars had higher nitrogen distribution in grain, and had lower nitrogen distribution in else vegetative parts at mature. The results indicate that the ability of accumulate and assimilate and distribute for 1990s'cultivars had higher than old cultivars (1950s,1960s,1970s), it was make for the form of grain yield. That is key physiological reason for grain yield enhancement during wheat cultivars improvement.In summary, the 1990s'cultivars could maintain Pn of leaves at different positions longer than the older cultivars during wheat improvement process. The post-anthesis decline of Pn in the older cultivars was associated with a reduction in the chlorophyll content and the soluble protein content. The newer cultivars and the older ones have different diurnal photochemical efficiency. A midday depression in photosynthetic rate occurred in all cultivars, which might be caused by serious photoinhibition. Then the newer cultivars have improved photosynthetic capacity:higher photosynthetic rate, larger green leaf area and longer leaf longevity. The newer cultivars not only could establish larger source and sink than the old ones, but also have the ability to optimally partition assimilations into grain.