Studies on the Characteristics of Differentiation and Degeneration of Spikelets and Grain-filling in High-yielding Rice Cultivars with Large Panicles

本研究旨在阐明近年来中国、韩国、菲律宾等国育成的大穗型高产水稻品种（LP-HYC）的颖花分化、退化和籽粒灌浆特性。研究结果如下：1.分化小穗数、退化小穗数和退化小穗率在LP-HYCs间差异较大，但二次枝梗分化小穗的退化小穗数远大于一次枝梗分化小穗的退化小穗数。SB上退化小穗的大部分来源于残存PB上的退化SB。分蘖期追氮LP-HYCs能增加每穗分化颖花数和穗数，但在增加退化颖花率的同时降低了存活颖花数.抽穗前40- 20天施氮、磷、钾可增加LP-HYCs的颖花分化和减少颖花退化，从而增加颖花存活数。抽穗前15 d的强遮荫和高昼夜温度增加了退化小穗的比例。颖花退化率随抽穗期茎干重和分化颖花干重的增加而降低.抽穗期茎鞘贮藏碳水化合物和抽穗后同化碳水化合物对籽粒灌浆的贡献率因品种和栽培条件的不同而有较大差异。

This study was conducted to clarify the characteristics of the differentiation and degeneration of spikelets and the grain-filling in high-yielding rice cultivars with large panicles (LP-HYC) bred in China, Korea, the Philippines and other countries in recent years. The results were summarized as follows ;1. The number of differentiated and degenerated spikelets, and the percentage of degenerated spikelets varied considerably among LP-HYCs, but the number of degenerated spikelets was much larger in the differentiated spikelets on the secondary rachis-branch (SB) than those on the primary rachis-branch of panicle (PB). The major part of degenerated spikelets on SB was derived from the degenerated SBs on the surviving PB.2. Nitrogen top-dressing at tillering stage to LP-HYCs increased the number of differentiated spikelets per panicle as well as the panicle number, but greater increase in the percentage of degenerated spikelets at the same time decreased the number of surviving spikelets.3. Nitrogen, phosphorous and potassium application at 40-20days before heading increased the number of surviving spikelets due to the increase in differentiation and the decrease in degeneration of spikelets in LP-HYCs. The heavy shading and high-day and/or night temperature during 15 days before heading increased the percentage of degenerated spikelets. The percentage of degenerated spikelets decreased with the increase of shoot dry weight per stem (SDW) and SDW per differentiated spikelets at heading.4. Contribution ratio of the stored carbohydrate in the culm and leaf sheath at heading and the assimilated carbohydrate after heading to the grain-filling varied so much among cultivars belonging to LP-HYC and by the cultivated conditions.