Effects of Non-Structural Carbohydrates on Spikelet Differentiation in Rice

Abstract

Spikelet number per unit area is a strong determinant of rice yield, and spikelet differentiation must be promoted to increase spikelet number. Nitrogen has been considered to be the most critical factor in promoting spikelet differentiation and the role of non-structural carbohydrates (NSCs) in spikelet differentiation is unclear. To reveal the relation between NSCs and the number of differentiated spikelets, we conducted a field experiment in Matsue, Shimane, Japan, using two japonica cultivars Koshihikari and Nipponbare. The NSC content was changed by shading and thinning during the early reproductive stage. These treatments did not change the amount of nitrogen per hill in the leaves and stems. The number of differentiated spikelets, which was defined as the sum of the numbers of surviving spikelets and vestiges of degenerated spikelets, was not influenced by NSC content in rice plants; neither was the number of primary rachis-branches, which is considered to determine spikelet number per panicle. The ratio of dry matter allocation to leaves and the rest of the plants was changed, but the morphological characteristics such as tiller number and plant length were not influenced by the treatments. It is concluded that the differentiation of spikelets was not influenced by the NSC content within the range examined in the present experiment. The role of NSC in the mechanism of spikelet differentiation is discussed.

Keywords

• Dry matter production
• Nitrogen
• Non-structural carbohydrate
• Rice
• Shading
• Spikelet differentiation
• Spikelet number
• Thinning