Distribution of Photosynthate in Rice Plant : 2. Changes in the ratio of ear to shoot at maturity caused by shading treatments at different growth stages.

Abstract

Shading treatments at different growth stages, reduced the dry weight of rice plants at maturity. Shading treatment during the period from the neck node initiation stage to the late spikelet initiation stage, reduced the dry weight of shoot at maturity, but not that of ear. Shading treatment during the period from the late spikelet initiation stage to the ear emergence, reduced the dry weight of ear at maturity, but not that of shoot. Shading treatment during ripening period, reduced the dry weights of ear and shoot at maturity. The dry weight reduction resulting from shading treatment was greater in extents in the case of ear than in the case of shoot at maturity. Therefore, the ratio of ear to shoot at maturity was greater for the treatment shaded during the period from the neck node intiation stage to the late spikelet initiation stage than for the control. And the ratio of ear to shoot at maturity was greater for the control than treatments shaded during the period from the late spikelet initiation stage to the ear emergence and ripening period respectively. In this experiment, the ratio of ear to shoot at maturity had no definite relation either with the ratio of the dry weight increased after the ear emergence to that at the ear emergence, or the ratio of the number of spikelets to the dry weight at the ear emergence, However, in all the treatments excepting those shaded during the period from the late spikelet initiation stage to the ear emergence, the ratio of ear to shoot at maturity was positively correlated with the ratio of the dry weight increased after the ear emergence to that at the ear emergence. And, in all the treatments excepting those shaded after the ear emergence, the ratio of ear to shoot at maturity was positivily correlated with the ratio of the number of spkelets to the dry weight at the ear emergence. In the treatments shaded during the period from the late spikelet initiation stage to the eer emergenece or ripening period, no definite relation was found between the dry weight increased after the ear emergence and the number of spikelets. From these facts, it could be said that the ratio of ear to shoot at maturity was first determined by the ratio of the number of spikelets to the dry weight at the ear emergenece, and then by the ratio of the dry weight increased after the ear emergence to the munber of spikelets.