| In order to illustrate the genotype differences and control approaches of nitrogen uptake and its utilization efficiency in different types of rice, 92 rice cultivars or hybrid combinations with wide genetic backgrounds collected from both domestic and abroad, and a population of recombinant inbred lines (RILs) which was derived from Zhenshan 97 × Minghui 63, parents of Shanyou 63, an elite Indica hybrid rice in China, were solution cultured in 1999 and in 2000, respectively. To investigate the differences of nitrogen uptake and its use efficiency in different types of rice, 92 rice cultivars or hybrid combinations were grouped into 6 types: conventional Japonica, CJ; conventional Indica, CI; wide compatible varieties, W; hybrid Japonica, HJ; trilinear Indica hybrids, THI; and bilinear hybrids, BH. The relationship of nitrogen uptake and use efficiency with root traits, plant height, growth duration, grain yield and sink property were analyzed, using both 92 rice cultivars or hybrid combinations and RILs. The putative QTLs (quantitative loci) controlling nitrogen uptake and use efficiency were identified, using molecular mark technique. Results showed as follows:1. The range of nitrogen content (NC) in rice plant for 92 cultivars or hybrid combinations was 1.216%-1.787%, and variation coefficient (cv) for NC was 6.491. NC at maturity in THI and BH plant body was higher than that in the rest of rice types. Rice cultivars with higher plant height and longer growth duration had higher NC. High-yielding cultivars had higher NC but NC showed no significant difference in cultivars with lower yield. Compared with NC at heading stage, NC at maturity decreased but cultivars with larger sink had larger decreased extent in NC.2. Abundant variation of nitrogen uptake was observed in tested cultivars and CV for nitrogen accumulation (NA) at heading and at maturity was 26.67 and 23.62,respectively, while ratio of maximum NA to minimum NA at heading and at maturity was 4.49 and 3.88, respectively. Of 6 types of rice, NA in BH ranked the highest, followed by THI, HJ, CI, CJ and W. Average NA at heading and at maturity of hybrids was 35.57% and 25. 82% higher than that of conventional cultivars, but NA after heading in hybrids was slightly less than that in conventional cultivars, and this result implied that hybrids as a whole presented their superior nitrogen uptake before heading rather than after heading. There existed significant positive correlation between NA and the number, length, absorption area of adventitious roots. Cultivars with higher plant height, longer growth duration had larger NA. As yield and sink increased, the nitrogen requirement of rice cultivars increased, and the slope became sharper when yield and sink was higher.3. The difference of nitrogen distribution percentage in various parts of rice plant was observed but the changing patterns varied with organs. In cultivars with higher plant height, more nitrogen distributed in leaf, stalk and sheath than in root and panicle. As growth duration increased, nitrogen distributed in panicle increased and that in stalk and sheath decreased, while nitrogen distribution in root green leaf remained stable. Effect of grain yield and sink on nitrogen distribution was not significant.4. In this study, wide compatible varieties (W) had highest nitrogen use efficiency for biomass production (NUEp) while NUEp in THI and BH was relatively lower. NUEp at maturity in all rice types was higher than that at heading, but the extent of the increment varied with types. NUEp positively correlated with root activity per unit of root fresh weight. NUEp of cultivars with high plant height was lower than that with low plant height. As sink increased, NUEp decreased. NUEp was not significantly correlated with growth duration and yield.5. Nitrogen use efficiency for grain output (NUEg) was rather abundant in this study and ratio of maximum NUEg to the minimum reached 3.89. Of 6 rice types, CI and THI had higher NUEg, followed by BH, while W had lowest NUEg.
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