Comparison of Assimilation Rates in Leaves at Various Nodes in Canopies of Three Spring Wheat Cultivars with Different Plant Forms

This study was conducted to reveal the ideotype of wheat (Triticum aestivum L.) canopy structure for high yield and biornass productivity. The assimilation rate and nitrogen contents of the flag, second, third and lower leaves and the ear of the main stem were measured in three spring cultivars with different plant forms (figures), Haruyutaka, Norin 61 and Selpek, under field conditions. The assimilation rate was evaluated based on the amount of water-soluble carbohydrate accumulated during the day (WSC/day). Surface area indexes of the ear and flag leaf in Haruyutaka and Selpek were larger than those in Norin 61. In Haruyutaka and Selpek, the amount of WSC/day was larger in the flag leaf than in the second or third leaf, which had a sufficiently high nitrogen content. On the contrary, in Norin 61, the amount of WSC/day in the flag leaf was similar to that in the second and third leaves during the grain-filling period. The amount of WSC/day in the flag leaf during the last half of the grain-filling period was much higher in Selpek than in Haruyutaka and Norin 61. This may be one of the reasons why Selpek had a heavier total dry weight than Haruyutaka and Norin 61 in 1993 and 1995