GRAIN YIELD AND ASSOCIATED PHOTOSYNTHESIS CHARACTERISTICS DURING DRYLAND WINTER WHEAT CULTIVAR REPLACEMENT SINCE 1940 ON THE LOESS PLATEAU AS AFFECTED BY SEEDING RATE

摘要

An experiment was conducted to verify how the grain yield and associated photosynthesis characteristics of wheat respond to seeding rate with cultivar replacement. Seven wheat cultivars released from 1940 to 2004 that were once widely grown on the Loess Plateau were grown in ?eld experiments during the 2011-2012 growing season at the Changwu experiment station in China using three seeding rates (100, 250, and 350 seeds m-2), using a randomized complete block with a split-plot design and three blocks. The grain yield increased linearly with cultivar development in all seeding rate treatments, with annual genetic gains ranging from 0.65% to 1.29%. The cultivars released after the 1980s were less sensitive to seeding rate and had better population regulation. The improvements in the harvest index and thousand grain weights of the modern cultivars were significantly and positively correlated with the grain yield. The photosynthetic rate of the flag leaf and the leaf area index at anthesis consistently increased with cultivar replacement, contributing more to the thousand-grain weight and resulting in grain yield increases. Diffuse non-interceptance at anthesis resulted in opposite, stable trends with time. One reason to adapt modern cultivars for modern cultivation is their lower sensitivity to seeding rate. Thus, larger sinks for the grains and the optimization of plant types for light interception should be given greater consideration in dryland wheat breeding on the Loess Plateau.