Characteristics for the Efficiency of Spikelet Production and the Ripening in High-Yielding Japonica-Indica Hybrid and Semidwarf Indica Rice Varieties.

Abstract

Three high-yielding japonica-indica hybrid (JIH) and semidwarf indica (SDI) rice varieties, and ten japonica (J) rice varieties, including different plant types, were cultivated under sparse (30×30 cm) and dense (20×20 cm) conditions to clarify the characteristics for the efficiency of spikelet production and the ripening in these high-yielding rice varieties in comparison with japonica rice varieties. 1) Brown rice yields in JIH and SDI were generally higher than those in J in both planting densities, because the number of spikelets per m2 of JIH and SDI, which mainly depended on the number of spikelets per panicle, especially those on the secondary rachis-branch, were greater than those of J. 2) The number of spikelets per m2 for the same level of leaf area index, top dry weight or top nitrogen content at heading stage was greater in JIH and SDI bearing bigger panicles than in J bearing smaller ones. 3) The number of spikelets per m2 of JIH and SDI, or that of J showed significant negative correlation with the percentage of ripened grains. Although the decline of percentage of ripened grains in each varieties was due to the increase of spikelets on the secondary rachis-branch, the percentage of ripened grans in JIH and SDI was higher than that in J at the same level of the spikelets number. 4) From the results mentioned above, it was suggested the high-yielding character in JIH and SDI was based on the greater spikelets per m2 due to the higher number of spikelets per panicle, and the less decline of percentage of ripened grains at this greater spikelets, in spite of the increase of the spikelets on the secondary rachis-branch, as compared with J.