Effects of spikelet removal on dark respiration and dry-matter production in rice

The reduction of the dark respiration at the ripening stage may increase the dry-matter production and yield in rice. The effects of spikelet removal on dark respiration and dry-matter production were examined under 4 levels of shading. The spikelets were removed to reduce the number of grains to zero, 1/3 or 2/3 of the intact plants. Control plants were left intact. The rate of gross photosynthesis (Pg) and panicle dry weight increased as light intensity increased and was higher in the plants with a larger number of grains. The dark respiration of the panicle was mainly related to the dry-matter increase of the panicles regardless of the number of grains. The rate of translocation from the leaf blade and stem to the panicle increased as the number of grains increased, but the dark respiration of the leaf blade and stem did not change. Thus the dark respiration per dry-matter translocated to the panicle was small in the plants with a large number of grains. The increase in Pg and decrease in the ratio of the dark respiration in the leaf blade and stem to Pg were responsible for the higher panicle dry weight in the plant with a large number of grains. It was concluded that in the plant with a large number of grains, the high Pg and the low consumption of carbohydrates in the leaf blade and stem contributed to the improvement of the growth efficiency and yield.