Abstract
To examine the possibility of breeding high-yielding cultivars with high nitrogen use efficiency for dry matter accumulation (NUEd) and to provide simple criteria for the selecting and breeding high-yielding cultivars with high NUEd as well as useful information for the mapping of quantitative trait loci (QTL) controlling NUEd, we cultured recombinant inbred lines (RILs) of rice hydroponically in 2000 and 2001. RILs with a higher grain yield tended to show greater total dry matter accumulation (TDMA) and higher harvest index (HI), while increasing TDMA resulted in a decrease in HI. The contribution ratio of the TDMA to grain yield (2000 : 67.3%, 2001 : 68.2%) was higher than that of HI in both 2000 and 2001. Even at the same high-yielding level, there was a significant difference in the TDMA and HI values. In both years, the contribution ratios of NUEd and total nitrogen absorption (NTA) to TDMA were about 62.0 and 38.0%, respectively. The contribution ratio of the NUEd to grain yield was higher than those of the NTA and HI in both 2000 (41.6%) and 2001 (42.9%). These results suggested that the high-yielding rice plants generally displayed high TDMA and HI values. Further increase in rice grain yield should be based on the further increase in TDMA than in HI, and to increase TDMA leading to a high grain yield, the emphasis also should be put on improving NUEd in RILs.
