Influence of removal of lower leaves and detaching of tillers on kernel weight of Hokkaido-bred wheat cultivar 'Haruyutaka' grown in a warm area of Western Japan.

摘要

In the Hokkaido-bred wheat cv. Haruyutaka grown in a warm district of western Japan, crop growth rate (CGR) during ripening period and kernel weight were low. The low CGR was caused by a low net assimilation rate (NAR), although the mean green surface area index (GAI) was high. Hypothesizing that an overluxuriant canopy of cv. Haruyutaka caused the low NAR, we released the canopy from the overluxuriant condition by removing the lower leaves or detaching tillers. We removed the lower leaves except for the flag and second leaves at the flag leaf expanding stage, or detached all tillers as the tillers emerged. The removal of lower leaves increased the kernel weight of cv. Haruyutaka in some seasons, when this defoliation increased NAR and CGR during ripening period. In addition, it increased the water-soluble carbohydrate (WSC) content of culms from anthesis to the milk ripe stage in cv. Haruyutaka, suggesting that the increased WSC was translocated to the grain at the maturation stage. Detaching of tillers decreased the number of ears and kernels, although it increased the 1000-grain weight. These results suggest that the removal of lower leaves could increase kernel weight by releasing the canopy from an overluxuriant condition, thus increasing grain weight, although it largely decreases the source:sink ratio in cv. Haruyutaka.