| Corn nitrogen use efficiency decreased remarkally with over-input nitrogen which induced many problems such as rising production costs and environmental pollution,the purpose of this study was to improved corn nitrogen use efficiency based on evaluation nitrogen use efficiency of different genotypes of maize inbred lines and hybrids and clarifying the physiological phenotypes of high nitrogen use efficiency(NUE). This study also provide a basis for selecting high NUE inbred lines and hybrids. The main conclusions were as follows:1. There were significant differences on nitrogen use efficiency of different corn genotypes.Based on the cluster analysis was performed for N partial factor productivity(PFPN), nitrogen harvest index(NHI) and yield. 52 maize inbred lines under traditional nitrogen input were divided into 24 high efficiency type and 28 low efficiency type; 108 hybrids were divided into 14 high efficiency type, 81 intermediate type and 13 low efficiency type under traditional nitrogen input;In high nitrogen, they were divided into 6 high efficiency type, 83 intermediate type and 19 low efficient type; 4 corn hybrids under two N treatments were divided into 2 high efficient type and 2 low efficient type..2. Through the evaluation of combining ability of nitrogen use efficiency and quality, nitrogen efficiency and quality of BL12, BL49, BL48, Zhong106 and Qi205 five maize inbred lines were better, and had greater nitrogen use efficiency and quality breeding potential. Crosses Y82(BL12× 178) and Y99(BL48×Ye 478) are high quality and efficient hybrids. With the treatment of low and high nitrogen, N efficiency was increased 11.95% and 28.69% compared with control, respectively. Grain yield were 13756.88, 13572.90 and 16460.13, 16269.55 kg/hm2, and were increased 3648.00 and 1458.27 kg/hm2 compared with control, respectively.3. The percentage of high NUE cross combinations with at least one parent was nitrogen efficiency of inbred lines under the treatment of conventional nitrogen and high yield nitrogen were 92.86% and 83.33%, respectively. But the percentage of both the parents were N inefficient type inbred lines were 7.14% and 16.67%, respectively. The results showed that the nitrogen efficiency of maize hybrid breeding to select at least one nitrogen efficiency of parents in equipping, with a higher chance of high NUE maize hybrid combinations.4. The essence of NUE physiological properties of different genotypes maize was the unit of source(photosynthesis), sink(photosynthesis products and transformations) and flow(kernel). In the canopy photosynthetic capacity, greater leaf area index, chlorophyll SPAD value, net photosynthetic rate and longer duration of photosynthesis were important guarantee for high photosynthetic capacity of kemel stage, and have good effects in photosynthetic performance of function leaves in stable late development. They were important factors to shape difference of grain yield of high and low N efficiency corn. In the point of grain yield and its components, the differences between high and low N efficiency were manifested in the grain number and weight per ear. It showed that the volume directly affected the grain yield, thus affected the NUE.In the respect of dry matter and nitrogen accumulation and transportation, about 60-90% grain yield of different nitrogen efficiency genotypes came from synthesis of dry matter after silking stage. The differences were determined together by stem dry matter before spinning period and synthesis of dry matter after silking stage.The essence was shown by the differences of economic index. The improvement of grain yield and NUE should not only focus on the shift in vegetative matters to seeds, but also insure the absorbing nitrogen ability after silking, to improve the ability of accumulating and transportation of matters.5. The root was the most major organs of crop nitrogen uptake, control and affect the growth of the whole plant under varies conditions. Nitrogen uptake depends on two aspects, one was the size of the root, another was the root absorption. Under the treatment of low or high nitrogen, root length(and<0.20mm), surface area and tips of maize genotypes with high N efficiency have a significantly higher level than low N efficiency, and the root activity of nitrogen efficient performance of inbred lines were significantly higher of 42.20% and 103.22% than the nitrogen-inefficient inbred, respectively. The results indicated that long roots, high proportion of fine roots and high absorptive capacity of root were the precondition and guarantee of high N absorption.6. Starting with the physiological property of source, sink and flow harmoniously of high N efficiency maize, nitrogen efficiency of different genotypes maize were evaluated. The chlorophyll SPAD value was used as source indicator, grain number per panicle and weight per thousand grains were used as sink indicator, and harvest index was used as flow indicator, to provide basis for selecting and evaluating nitrogen efficiency type of different genotypes maize, screening high-yielding and high N efficiency hybrids and systematical comparison of physiological properties of different corn truly and quickly, and also to provide the basis for improving varieties and high yield and high efficiency cultivation. |
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