Abstract
Changes in the number and size of spikes, grains, endosperm cells and starch granules was examined in relation to the limited assimilates caused by shading treatments. Spring wheat canopy (Triticum aestivum L. cv. Haruyutaka) was covered with a 95% shading cloth so as to cause failure in the assimilation at the initial, early and late grain filling phases; initial shading, from two days before anthesis until seven days after anthesis; early shading, from seven days until 14 days after anthesis; and late shading, from 14 days until 21 days after anthesis. The grain yield decreased (11% as compared to no shading) due to a decrease in the number of grains (17%), especially decreasing (62%) at the third floret position in the initial shading, while a decrease of one grain weight at all floret positions resulted in 20% and 16% decreases in the grain yield in early and late shadings, respectively. The reduction of grain weight was not due to a decrease in the number of endosperm cells, but to a decrease in the size of large starch granules. Differences in the effects of shading on changes in sink characters could be explained in terms of the physiological process of grain formation.
