Study On The Grain Filling Characteristics Of Dry Land Winter Wheat Varieties In The Process Of Replacement In Different Years

With the replacement of cultivars, agronomic traits and yield potential of wheat have different degrees of changes. The increase of production levels resulting from variety alternative has been shown in several studies. Nowadays there’s a ton of researches focus on the response of yield to ambient conditions in Grain Filling Stage. And confirmed the final yield was influenced by seedtime, water and fertilizer conditions and other ecological factors,such as temperature and drought directly or indirectly. Grain filling stage is the most important stage for grain weight accumulation. Because the grain filling process is variant in different grain and ear positions, the final grain weight has prominent difference in different part of panicle, and leading to a low and unstable yield. It is therefore necessary for the development of high yield potential wheat to validate the association between filling characteristics and yield potential in replacement process.In this study, field experiments with two different water treatments were conducted using the Northwest representative wheat cultivars developed between 1940 and 2010. The filling characteristics of different winter wheat varieties and their influence on the yield were explored, the variation of filling characteristic of strong particles and sick particles, the regulatory pathway of grain filling rate and stability were analyzed. It will provide a reference for comprehending the physiological mechanism of increasing grain yield and analyzing the improvement potential and breeding efficiency of wheat varieties. The main results obtained are as follows:1. The thousand seed weight increased gradually with cultivar replacement, coupled with the increase of filling rate and filling duration. There are differences in grain weight accumulation and filling characteristics between different varieties and grain position,(1)Compared with water varieties, dryland winter wheat varieties were less affected by water condition and had no obvious differences in grain weight between two water levels. And modern dryland varieties maintained a higher filling rate and filling duration under drought conditions. In addition, the filling rate of dryland cultivars under drought condition is higherthan water condition, that’s perhaps the reason why dryland varieties remained high weight under drought condition.(2) With the variety replacement, grain weight and the average filling rate of superior and inferior grains of dryland wheat varieties increased gradually,whereas the filling days increased unsteadily. The theoretical maximum grain weight of superior grain under drought condition increased apparently relative to the reduction in inferior grains. This may be caused by the amounts of dry matter accumulation in the period of rapid growth. A sharp decline in the filling intensity was presented in inferior grains among this period, resulting in a reduction of grain weight accumulation. As a consequence of this,drought stress promoted the accumulation of superior indirectly by inhibiting the development of inferior grains. The improvement of filling rate, especially the liner and mature period, will contribute to the accumulation of grain weight.2. The yield potential was improved in different extent with the cultivars replacement. In the present study, thousand seed weight and yield of dryland winter wheat varieties under both water treatments showed a trend of increasing. And the substantial increase in production was accompanied by the improvement of grain weight accumulation. Our research also indicated that it presented a positive correlation between the grain weight and filling rate in dryland winter wheat under drought condition. Except for the highly significant positive correlation with filling rate, grain weight also had a strong correlation with filling days under water treatment. Thus it can be seen that the grain weight of the whole spike not only affected by the filling rate but also was related closely with the filling duration under different external environment. Moreover, the grain weight of superior and inferior grain was positively correlated with the filling rate, respectively. And inferior grain weight was significant positive correlated with grain filling rate in the liner period. In conclusion, it is crucial for yield improvement of dryland winter wheat to increase the filling rate at various filling stages.3. This study showed the growth process of winter wheat was accelerated and the grain filling duration was shortened under drought stress condition, but the modern varieties were influenced lighter compared to earlier varieties. The average filling rate of early varieties under drought stress decreased slightly, whereas the average filling rate of modern varieties,Changwu134 and changhan58, were increased. In addition, the grain weight accumulation and filling rate of wheat grains decreased rapidly in the middle and late stage of grain filling under drought condition, and the reduction of inferior grains was more significant. This shows that the soil moisture condition is one of the most important limiting factors in the middle and late stage of grain filling. Because of the sensitivity of inferior grains, water deficit affected the whole spike grain weight accumulation to some extent. Moreover, the declining range of yield in modern cultivars was more significant than earlier varieties. As aconsequence, although the replacement of cultivars improved the yield potential of wheat greatly, the yield of modern varieties was more susceptible to moisture conditions and became more unstable.4. Compare with modern varieties, the earlier cultivars had a weaker storage capacity and less dry matter accumulation, followed by the weakening of grain weight increase,resulting in a lower yield. Therefore, it is also crucial for yield improvement to coordinate the source-sink relations of dry matter accumulation and nutrients transfer organs. In addition,the difference of the sink capacity was significant among varieties. Because of a characteristic of less number of spikes, lighter grain weight, the earlier cultivars has a lower storage capacity, as a consequence of limiting the accumulation of grain weight and the play of grain weight advantages. But the storage capacity of modern cultivars had been optimized,especially the sink capacity of superior was increased greatly, which led to a significant increase of yield. In the case of the influence of yield components to the yield, the number of productive ear had a large contribution to production and played an active role in production improvement under drought condition. Owing to the instability of the number of productive ear per unit area of dryland wheat, we should give priority to the number of productive ear in the selection of breeding traits.