The Analysis of the Process in Spikelet Number Determination with Special Reference to Nitrogen Nutrition in Rice

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The relationship between spikelet number per unit area (spikelet density, SD) and spikelet number components (SNCs) was analyzed. The spikelet density was the product of five SNCs: panicle number per unit area (PN), the number of differentiated primary rachis-branches per panicle, the number of differentiated secondary rachis-branches per differentiated primary rachis-branch (SB), the number of differentiated spikelets per differentiated secondary rachisbranch, and spikelet degeneration percentage. The relationship between SNCs and shoot nitrogen (N) or dry weight (DW) was also researched. By using multiple regression analysis, the PN and the SB were the most and the next most contributory factors to the SD, respectively. The PN and the SB had the highest correlation with N amount at the early spikelet differentiation stage (ESD) and the increment of N concentration from panicle initiation (PI) to ESD, respectively. It is concluded that the SD can be expressed by three parameters by using multiple regression analysis, which the parameters were N amount at the ESD, the increment of N concentration from PI to the ESD, and the DW , per differentiated spikelet at heading.