Characteristics Of Yield Formation And Grain Quality Of Rice CSSSLs With High Nitrogen Utilization Efficiency Under Low Nitrogen Supply Level

Under field condition with low nitrogen supply level,114 rice Chromosome Single Segments Substitution Lines (CSSSL) were analyzed in 2012 and 2013. The source and sink relationship, dry matter production and distribution, nitrogen absorption and distribution, grain yield and yield components were determined. Based on nitrogen-use-efficiency by grain output (NUEg), the rice CSSSLs were clustered into 6 types (A, B, C, D, E, F) by the dynamic clustering method MinSSW (Minimum Sum of Squares within groups). The differences of the above traits among rice types with different NUEg and their relationship with NUEg were analyzed. Three CSSSL lines with typically higher NUEg and 3 with typically lower NUEg were chosen to analyze grain quality in 2014. These analysis clarified the major factors influencing the rice NUEg under the condition of low nitrogen supply level, the basic characteristics of higher-NUEg rice in terms of source and sink relationship, dry matter production and distribution, nitrogen absorption and distribution, grain yield and yield components, and the rice grain quality. This study aimed to provide fundamental information for effective utilization of nitrogen for high-yield cultivation and genetic improvement of NUEg in rice breeding. The results were as follows:1. There were significant differences in NUEg among different rice types. The type with highest NUEg was 2.23 times of the lowest one. The variation within different types was of great extent.2. Rice yield increased significantly along the increase of NUEg. Rice types with high NUEg showed significantly higher rice yield than those with low NUEg. The same trend was found in the theoretical yield and the actual harvest yield between typical rice lines with higher NUEg and lower NUEg. There was significant positive correlation between the NUEg and the grain yield (r=0.510**), as well as between the N uptake and the grain yield (r=0.657**). Direct path coefficient of the N uptake to the grain yield was 0.889, while that of the NUEg to the grain yield was 0.77. These results indicated that improvement of both N uptake and NUEg could lead to enhancement of grain yield level. Though the contribution effect of the N uptake to grain yield is larger than that of the NUEg, but it is smaller in low nitrogen supply condition compared with that in normal nitrogen supply condition.3. In terms of the yield components, the spikelet number per panicle, filled grain percentage and grain weight per panicle in CSSSLs with higher NUEg were high, whereas the panicle number per unit area did not show advantage. The NUEg was not significantly correlated with 1000-grain-weight.4. In terms of the source and sink relationship, rice types with higher NUEg showed lower LAI in maturity stage, bigger sink capacity and sink capacity per panicle and higher grain yield per unit leaf area. No significant correlation between LAI at heading stage and the NUEg was found in this study.5. In terms of the dry matter production and distribution, no significant difference was found in dry matter production (at both heading and maturity stage) and proportion of dry weight at heading stage among the different rice CSSSL groups. While rice CSSSL types with higher NUEg showed lower proportion of stem and leaf dry matter weight at both heading and maturity stage, higher proportion of panicle dry weight, higher ratio of dry matter translocation from stem and leaf during grain filling period. Consequentially, it displayed a higher economic coefficient.6. In terms of the nitrogen uptake and distribution, the whole plant N content (%)at heading stage (primarily in stem), at maturity stage (including stem, leaf and panicle) and the N uptake at maturity stage all decreased while NUEg improved. The nitrogen translocation rate from stem & sheath to panicle in rice lines with higher NUEg was higher than those with lower NUEg during grain filling period, which were characterized by higher nitrogen use efficiency (including nitrogen efficiency by plant biomass, nitrogen harvest index and NUEg).7. In terms of rice grain quality,(1) The rice types with higher NUEg displayed higher brown rice percentage (significant) and milled rice percentage than types with lower NUEg. No significant difference was found in head rice percentage between rice types with different NUEg at maturity stage.(2) Rice types with higher NUEg showed a tendency of higher chalky grain rate and chalkiness,slightly lower grain length-width ratio than those with lower NUEg, but did not reach significant level.(3) The grain protein concentration in the rice types with higher NUEg was significantly lower than those with lower NUEg. The accumulation of Cu, Fe, Mn, Zn, Ca, K, Mg and P in the brown rice of types with higher NUEg were higher than those in rice with lower NUEg, the differences ranged from 33.33%-47.63%. Among them, the differences of Zn, Ca, Cu, K, Mg and P were significant, Fe and Mn were close to be significant level. The accumulation of Cu, Fe, Mn, Zn, Ca, K in the milled rice of types with higher NUEg were higher than those in types with lower NUEg, the differences ranged from 36.43%-65.02%, and the accumulation of Zn, Ca, Cu, Fe and K were significantly different between 2 rice types, Mn was close to be significant. The accumulation of the analyzed elements in the brown and milled rice showed significant or very significant linear correlation with the grain yield except Mg. The content of Zn, Ca, Mg and P in the brown rice of types with higher NUEg were lower than those with lower NUEg, the difference ranged from 7.18%-9.81%. While P and Mg showed significant differences, Zn and Ca were close to be significant.In the milled rice, the content of Zn and Ca were lower in types with higher NUEg than those with lower NUEg, but it had not reached significant levels. The content of Cu and Zn in the milled rice showed significant linear correlation with the protein concentrations. The concentration of total amino acid in the milled rice of types with higher NUEg were lower than those with lower NUEg, with a difference of 9.13%. The essential amino acid did not show significant differences, with, isoleucine, leucine, phenylalanine and lysine showed a decreasing tendency, ranging from 9.67%-10.71%. The concentration of leucine and phenylalanine showed significant differences between the two rice types, isoleucine and lysine were close to be significantly different.