Genetic Dissection Of Nitrogen Use Efficiency And Related Traits In Rice At Different Nitrogen Levels

In modern farming system, the excessive use of nitrogen fertilizers results in increasingly severe adverse effects to the environments, the problem of nitrogen uptake and use efficiency stepwise decreased is usually accompanied with the greater increased nitrogen application. Undoubtedly, improvement of grain nitrogen use efficiency is one of most important goal in modern rice breeding program. Therefore, selection for high nitrogen use efficiency with high grain yield for decreasing the cost of rice production and environmental pollution remains a big challenge in rice breeding.The objectives of this study were:1) to investigate the relationships between grain nitrogen use efficiency and grain yield and its component under two nitrogen levels, and mapped QTLs for these traits;2) to study the relationships between grain nitrogen use efficiency and rice tissue nitrogen concentration traits under two nitrogen conditions, and detect QTLs for these traits;3) to examine the relationships between grain nitrogen use efficiency and nitrogen accumulation and translocation traits under two nitrogen levels, and identify QTLs for these traits;4) to explore the relationships between nitrogen use efficiency and nitrogen deficiency tolerance traits under two nitrogen conditions, and investigate QTLs for these traits. The results of QTLs mapping will provide useful information for the improvement of nitrogen use efficiency and related traits with marker assistant selection. The2006experiment was conducted at Xusan villiage, Xiaogan City (30°56'N,113°54'E), while the2007experiment was carried out at Dajin town, Wuxue City (29°51'N,115°33'E). For low-nitrogen (LN), no artificial nitrogen fertilizer was applied. For normal nitrogen (NN),135kg N ha-1in2006and130kg N ha-1in2007were applied. The following results were obtained:1) Grain nitrogen use efficiency was significant positively correlated with grain yield, grain filling and the number of spikelets per panicle under both nitrogen conditions, suggested that grain nitrogen use efficiency may be improved though the improvement of grain yield, grain filling and the number of spikelets per panicle. For grain nitrogen use efficiency, two QTLs under LN and two QTLs under NN were identified in2006; four QTLs under LN and two QTLs under NN were detected in2007; all of these QTLs were located on chromosome1,2,6,7and11. For grain yield and its components, eighteen QTLs under LN and eighteen QTLs under NN were detected in2006and fifteen QTLs under LN and seventeen QTLs under NN were detected in2007, which were positioned on chromosome1,2,3,4,5,6,7,10and11. The close linkage genomic regions, including C86-C567on chromosome1, RM53-R1738on chromosome2and RZ471-C1023on chromosome7, were confirmed to affect most of grain nitrogen use efficiency, grain yield and yield component under both nitrogen conditions, and provided genetic basis of the relationship between grain nitrogen use efficiency, grain yield and yield component. All of these genomic regions would be very useful for improving nitrogen use efficiency in rice breeding though marker assisted selection.2) Grain nitrogen use efficiency was significant negatively correlated with nitrogen concentration traits at heading and maturity stage under both nitrogen conditions, suggested that grain nitrogen use efficiency may be improved though decreasing nitrogen concentration traits. Sixteen QTLs under LN and nineteen QTLs under NN in2006for rice tissue concentration were identified on chromosome1,2,4,6,7,8and10, and thirteen QTLs under LN and seventeen QTLs under NN in2007were identified on chromosome1,2,3,6,7,10and11. The close linkage genomic regions, including C86-C567on chromosome1, RM53-R1843on chromosome2, R2749-R1952a on chromosome6and RZ471-C1023on chromosome7, were confirmed to affect most of tissue nitrogen concentration traits and grain nitrogen use efficiency under both nitrogen conditions, and provided genetic basis of relationship between tissue nitrogen concentration traits and grain nitrogen use efficiency. This would be very useful for improving nitrogen use efficiency in rice breeding though marker assisted selection.3) Grain nitrogen use efficiency was significant negatively correlated with nitrogen accumulation traits at heading and maturity stage, however, positively correlated with nitrogen translocation traits under both nitrogen conditions, suggested that grain nitrogen use efficiency may be improved though decreasing nitrogen accumulations and increasing nitrogen translocation efficiency. For nitrogen accumulation traits, nine QTLs under LN and twelve QTLs under NN in2006, and ten QTLs under LN and eight QTLs under NN in2007were identified on chromosome1,2,3,4,5,6,7,9,10and11. For nitrogen translocation traits, nine QTLs under LN and eight QTLs under NN were detected in2006 and thirteen QTLs under LN and eight QTLs under NN were detected in2007, which were located on chromosome1,2,3,4,5,6,7,10,11and12. The close linkage genomic regions, including RZ5993-R1738on chromosome2, R1962-C1496on chromosome6, RZ471-C1023on chromosome7, G44-RG118and R3203-RM20a on chromosome11, were confirmed to affect most of all traits under both nitrogen conditions, and provided genetic basis of relationship between grain nitrogen use efficiency, nitrogen accumulation and nitrogen translocation traits.4) Nitrogen deficiency tolerance traits were the ratio of a trait value under LN to NN, including grain yield, biomass yield, grain nitrogen and biomass nitrogen. Nitrogen use efficiency traits were nitrogen response, grain yield response and physiological nitrogen-use efficiency. Nitrogen use efficiency traits significantly negatively correlated with nitrogen deficiency tolerance traits in the two testing years, except for the correlations between physiological nitrogen-use efficiency and relative biomass nitrogen. For nitrogen deficiency tolerance traits, seven and eight QTLs were identified in2006and2007, respectively. These QTLs were on chromosomes1,2,3,4,7,9,10and11. For nitrogen use efficiency traits, five and six QTLs were detected on chromosomes1,2,3,4,6,7,9,10and11in2006and2007, respectively. Four genomic regions, including G393-C922on chromosome1, RM232-C63on chromosome3, G235-G102on chromosome4and RG678-R1440on chromosome7, were found to contain QTLs for nitrogen deficiency tolerance and nitrogen use efficiency traits, provides partial explanation and genetic mechanism for the observed correlations between nitrogen deficiency tolerance and nitrogen use efficiency traits, and could be used as targets for improving nitrogen deficiency tolerance and nitrogen use efficiency traits in future breeding.