Abstract
Pattern of floret differentiation at each spikelet position of developing spikes of nine wheat cultivars was investigated in three successive growing seasons, from 1999 to 2002 in Yamaguchi. The results obtained by early sowing were compared with those obtained by standard sowing. These cultivars had different degrees of winter habit and were raised in different districts. This experiment was done to determine the change in spikelet number caused by early sowing in these cultivars. The florets differentiated earlier at the center than at the base or tip of the developing spike in standard sowing in all cultivars. In early sowing, they also differentiated earlier at the center of the spikelet in spring habit and strong winter habit cultivars. On the other hand Iwainodaichi and Airakomugi, the mild winter habit cultivars bred in Kyushu and Kanto districts differentiated florets earlier at the tip than at the center or base of spikelets in early sowing. The spikelet numbers per spike were larger in early sowing than in standard sowing in Iwainodaichi and Airakomugi in all three seasons, while they were smaller in early sowing than in standard sowing. Nevertheless, in Iwainodaichi and Airakomugi, the kernel number was smaller at the tip than at the center of the spikelet in early sowing, even though the florets differentiated earlier at the tip than at the center of the spikelets.
