Abstract: In order to provide basis for high-yielding cultivation of spring wheat in semi-arid region, a field experiment was carried out in Dingxi of Gansu Province, Northwest China in 2010 to study the effects of different sowing dates (March 8, March 18, March 28, and April 7) on the growth and development and yield formation of spring wheat. With the delay of sowing date, the days from sowing to heading stage shortened, resulting in an evident shortening of the whole growth period. Before late May, the earlier the sowing, the larger the leaf area index (LAI) was; after late May, the later the sowing, the larger the LAI. Early sowing made the peak of LAI advanced, while late sowing postponed the peak of LAI. Before late June, the earlier the sowing, the higher the chlorophyll content was; after late June, the earlier the sowing, the faster the decline of chlorophyll content. The population growth rate and net assimilation rate after heading stage had significant differences among different sowing dates, being the highest when the sowing date was March 18 and the lowest when the sowing date was April 7. Whatever the sowing date, the dry matter accumulation of wheat plants increased rapidly at jointing stage. Early sowing made the dry matter accumulation before jointing stage slower. With the delay of sowing date, the dates with the peak values of dry matter accumulation rate advanced, those with the peak values of grain filling rate postponed, and the
1000-kernel weight decreased after an initial increase. Sowing date had significant effects on the grain parameters at three grain filling phases. The grain yield differed significantly with sowing dates, being the highest when the sowing date was March 8.

Key words: Tricholoma matsutake, entophytic bacteria, community structure, PCR-DGGE, growth-promoting bacteria.