Analysis of the Number of Spikelets per Panicle on the Main Stems, Primary and Secondary Tillers of Different Rice Genotypes Grown under the Conventional and Nitrogen-Free Basal Dressing Accompanied with Sparse Planting Density Practices

Abstract

The number and development of spikelets on a panicle directly affect the grain yield. In this study, we examined the differences among various rice cultivars in the number of spikelets per panicle (NSP^-1) on the main stems (MS), primary tillers (PT) and secondary tillers (ST), and in the numbers of spikelets on the primary and secondary rachis branches. The difference among cultivars in the responses of these characteristics to the practice of nitrogen-free basal dressing accompanied with sparse planting density (BNo) was also elucidated. The results showed that NSP^-1 varied with the tiller position on a plant, and it was highest on MS followed by PT and ST in this order in all cultivars. NSP^-1 on all MS, PT and ST also varied with the cultivar, and was larger in the cultivars of the panicle-weight type than in those of the panicle-number type. The difference between MS and ST in NSP^-1 was larger in the cultivars of the panicle-weight type than in those of the panicle-number type.NSP^-1 was larger in BNo than in the conventional cultivation (CONT) in most cultivars. The difference between BNo and CONT in NSP^-1 varied with the tiller position on a plant and with the earliness of the cultivar, but did not clearly vary with the plant type of the cultivar. It was larger in the panicle on ST than on MS or PT, and was larger in the late-maturing cultivars than in the early- and medium-maturing ones. The larger NSP^-1 on MS or PT compared with ST, in the cultivars of the panicle-weight type compared with those of the panicle-number type, and in BNo compared with CONT was mainly attributed to the increased number of spikelets on secondary rachis branches.