Abstract: 【Objective】 The objective of this study was to explore the genetic difference of the nitrogen use efficiency (NUE) of different wheat lines from the middle and lower reaches of Yangtze River and screen out the lines with high NUE, which would provide useful germplasm for wheat high NUE breeding and lay a foundation for uncovering the underlying molecular mechanism. Meanwhile, correlation analysis between NUE and the related traits at different developmental stages of wheat would provide evidences for evaluating the high NUE wheat lines.【Method】The experiment was performed with 118 wheat cultivars mainly from the Yangtze River region in the field conditions by setting low (62.55 pure N kg·hm^-2) and normal (187.5 pure N kg·hm^-2) nitrogen inputs. The genetic variations and correlation analysis were further analyzed by characterizing the traits of dry above-ground mass, tiller number, chlorophyll content at the seedling stage; the dry above-ground mass, plant nitrogen concentration and accumulation at flowering stage; the chlorophyll content at the grain-filling stage; the yield, straw weight, kernel and straw nitrogen concentration and accumulation, spike number, spike length, kernel number per spike, and thousand kernel weight at harvesting stage with individual lines. Finally, classification of the wheat lines according to the respective NUE of each line was undertaken.【Result】The results showed significant genetic variations for most of the tested characters among different wheat lines. Correlation analysis indicated a positive correlation between yield and aboveground dry mass, straw weight, harvest index, spike number of the plant at harvesting stage, dry mass of the plant at the flowering stage as well as the nitrogen accumulation in the kernel and straw of the plant. Meanwhile, except the nitrogen harvest index, a negative correlation was observed between the plant physiological use efficiency and plant straw weight, spike number, kernel and straw nitrogen concentration and accumulation. In addition, according to the yield of the 118 wheat lines under the both nitrogen conditions, the selected wheat lines were categorized into four classes: Efficient-efficient (EE, yield higher than the mean yield of all the lines under both conditions), Inefficient-inefficient (II, yield lower than the mean yield of all the lines under both conditions), and Inefficient-efficient (IE, yield higher than the mean yield of all the lines only under high nitrogen conditions), Efficient-inefficient (EI, yield higher than the mean yield of all the lines only under low nitrogen conditions). The EE type of wheat lines was more sensitive to the nitrogen application. The EI type of wheat lines had significant higher chlorophyll content than the other lines at grain-filling stage, which indicated the critical role of stay-green character of the plant for nitrogen utilization under the low nitrogen conditions.【Conclusion】The selected wheat lines showed significant genotypic variations for their nitrogen use efficiencies under the two nitrogen input conditions. Meanwhile, the different types of wheat lines responded distinctively to the nitrogen application. Among them, the IE type of wheat lines was the most sensitive one to nitrogen application, and suitable for high nitrogen content field, whereas the EE and EI types were more tolerant to the nitrogen starvation, and could be the elite germplasm for high NUE wheat breeding. According to the correlation analysis of yield with different traits, it was found that except the routine characters such as the above-ground dry mass and plant nitrogen accumulation, the spike number could also be used as a trait to evaluate the high nitrogen use efficiency in wheat.

Key words: Wheat, the middle and lower reaches of Yangtze River, nitrogen use efficiency, genotypic variation, correlation analysis