Abstract
Developmental process of spike in winter type wheat Iwainodaichi sown early and its relationships with spike traits such as spikelet number, floret number, grain number, mean grain weight and grain weight per spike were compared with those in Iwainodaichi sown later and spring type wheat Chikugoizumi. Spikelet number per spike of Iwainodaichi was larger than that of Chikugoizumi, probably due to the longer duration from sowing to terminal spikelet formation, which determines the number of spikelets. Floret number per spikelet of Iwainodaichi tended to be smaller than that of Chikugoizumi perhaps due to the shorter duration from terminal spikelet formation to anthesis, which determines the number of florets. As a result, floret number per spike of Iwainodaichi was larger than that of Chikugoizumi. Grain number per spike of Iwainodaichi was larger in the plants sown in 1998 but smaller in the plants sown in 1999 than that of Chikugoizumi, since the ripening ratio of Iwainodaichi was smaller than that of Chikugoizumi sown in 1999. Grain number per spike was also smaller the earlier the sowing. Spike traits of Iwainodaichi sown early were different from those of Chikugoizumi and those of Iwainodaichi sown later, and some of those traits were related to the developmental process of spike. Grain weight per spike of Iwainodaichi sown early, however, was not different from that of Chikugoizumi or from that of Iwainodaichi sown later, since some of those spike traits were negatively correlated.
