Diversity of the Rachis-Branching System in a Panicle in Japónica Rice

Recently, rice varieties having large panicles with many spikelets are expected to produce high yield. However, the ripening, growth pattern, priority to photoassimilate partitioning and final grain weight in each spikelet vary with the position of the spikelet in a panicle. Therefore, not only the panicle size but also rachis-branching system in a panicle is an important factor determining the yield. In this report, we performed principal component analysis to characterize the rachis-branching system in 65 japónica varieties. In the principal component analysis, the proportions of variability explained were 49.6 and 22.2% for the first two attribute components. The first principal component was assumed as the factor of size in number, and the second principal component was assumed as the factor of shape of panicle. The distribution of the scores for each variety in the scatter diagram showed a large diversity in panicle characteristics in japónica varieties. A small number of varieties had scores distributed in the first quadrant of the scatter diagram. These varieties would be high-yielding because the number of spikelets is high in the panicle having a relatively large number of primary rachis-branches compared with the secondary rachis-branches. Some clusters in the scatter diagram were related with their origins