Abstract
It has been generally believed that the crop ideotype canopy has an erect small leaves to allow the photosynthetically active radiation (PAR) to penetrate deeply. In wheat, this might be not always applied to high-yielding varieties. We investigated the morphology and the PAR distribution in canopy (400 plants m-2) for three varieties with different canopy structures at early and late sowing times (April 13 and May 10, respectively). These three varieties, semi-dwarf early Norin 61 bred in Kyushu Japan, semi-dwarf early Haruyutaka bred in Hokkaido Japan, and tall late Selpek bred in Germany, differ from each other in canopy structure. Surface areas of ears and lower leaves were larger in early sowing than in late sowing for the three varieties, while those of flag leaves were larger in late sowing. Surface area of ears was larger for long-awned Haruyutaka than for short-awned Norin 61 and awnless Selpek, so that PAR penetration under the ears was lower for Haruyutaka. Surface area of flag leaves was larger for Haruyutaka and Selpek than for Norin 61, so that PAR penetration under flag leaves was lower for these varieties. However Haruyutaka and Selpek yielded their biomass higher than Norin 61. PAR penetration under lower leaves was higher in late sowing, and was especially high for Norin 61 and Selpek. On the other hand, there were significant negative relations between surface areas and PAR penetrations within layers of ears, flag leaves and lower leaves. Regression analysis showed that the horizontal flag leaf intercepted the PAR more effectively than the erect lower leaves. Culm surface areas seemed to intercept 27% of PAR within the flag leaf layer and 51% of PAR within the lower leaf layer.
