Relationship between Apical Dome Diameter at Panicle Initiation and the Size of Panicle Components in Rice Grown under Different Nitrogen Conditions during the Vegetative Stage

Abstract

SummaryA pot experiment was conducted to analyze the relationship between the size of each apical dome (AD) and the numbers of differentiated primary rachis-branches (PBs) and spikelets. Two rice cultivars were used : one was a heavy-panicle type ‘Akenohoshi’ and the other was a many-tillering type ‘Nipponbare’. Rice plants were applied nitrogen (N) at various rates (75-600mg N pot–1 week–1) during the vegetative stage. The base diameter and the height of ADs were measured at the panicle initiation (PI) stage. At heading, the numbers of differentiated PBs, secondary rachis-branches (SBs), and spikelets were counted. The N treatment increased shoot N concentration in both cultivars. The N treatment increased the base diameter of AD in Akenohoshi at the PI stage, but not in Nipponbare. The ADs in Akenohoshi had a base diameter about 6.2% larger on average than that in Nipponbare. The N treatment did not affect AD height. In Akenohoshi, the plants with a larger AD base diameter differentiated more PBs per panicle and then differentiated more SBs and spikelets than did those plants with a smaller AD diameter. However, in Nipponbare, the N treatments did not affect the number of differentiated PBs per panicle. These results suggest that the AD size at the PI stage, which is enlarged by higher N nutrition in the vegetative stage, is a determinant of the number of differentiated PBs and spikelets and that a larger AD size is responsible for a higher number of PBs and spikelets in Akenohoshi.