Abstract: 【Objective】To investigate the interactions between genotype, nitrogen application rate and planting density on the regulation of wheat lodging resistance and grain yield, and to identify the optimal combination of nitrogen-density that matches the biological characteristics of varieties, and to provide theoretical basis and technical support for stable and abundant winter wheat yield and resistant strain cultivation. 【Method】A split-split plot field experiment was conducted in Jiaozuo, Henan Province, China, for two consecutive years from 2020 to 2022, in which two wheat varieties, Xinhua 818 and Xinmai 26, which differ in resistance to overturning, were selected as the main plots; The nitrogen fertilizer application rates were used as split-plots, and five levels were set: no N application (N0), 180 kg·hm^-2 (N1), 240 kg·hm^-2 (N2), 300 kg·hm^-2 (N3) and 360 kg·hm^-2 (N4); the planting densities were used as split-split plots, and three levels were set: 2.25 million plants/hm^-2 (D1), 3.75 million plants/hm^-2 (D2) and 5.25 million plants/hm^-2 (D3). The study focused on analyzing the effects of the three-factor combination of variety, nitrogen application and planting density on the anatomical structure of wheat culms, field lodging rate and yield. 【Result】The results showed that nitrogen application rate and planting density significantly regulated the vascular bundle structure of both wheat varieties, and the number and area of big vascular bundles and the ratio of number and area of big and small vascular bundles were significantly and positively correlated with culm wall thickness and culm breaking strength, while the area of small vascular bundles was significantly and negatively correlated with culm wall thickness. Compared with Xinmai 26, Xinhua 818 had more number of big vascular bundles and larger area than Xinmai 26, while the number of small vascular bundles was equal and the area was smaller. This may be the anatomical basis for the superiority of Xinhua 818 over Xinmai 26 in terms of lodging resistance. Under the same planting density, the number and area of big vascular bundles of both wheat varieties showed a trend of increasing and then decreasing with the increase of nitrogen application rate, with the largest number and area of big vascular bundles in N3 treatment, and the average increase of number and area of big vascular bundles of Xinhua 818 and Xinmai 26 under N3 treatment compared with the minimum treatment were 14.61%, 15.80% and 16.18%, 20.10% respectively, and the number and area of small vascular bundles showed similar changes. Under the same level of nitrogen application rate, the number and area of big vascular bundles of both varieties were the largest in the low density D1 treatment. Compared with the minimum value of high density D3, the average increase in the number and area of big vascular bundles of Xinhua 818 and Xinmai 26 under D1 treatment were 6.14%, 5.20% and 8.95%, 11.42%, respectively.【Conclusion】Nitrogen density control combination D1N2 with 240 kg·hm^-2 and planting density of 2.25 million plants/hm² can optimize the vascular bundle structure, coordinate the development of big and small vascular bundles, increase the number and area of big vascular bundles, increase the number and area ratio of two types of vascular bundles, enhance the thickness of the culm wall between the basal nodes, and improve the breaking strength of the plant, which can achieve the simultaneous improvement of the lodging and yield of winter wheat. It can be used as a suitable nitrogen-density combination pattern for high-yielding and efficient cultivation of winter wheat in high-yielding irrigation areas in northern Henan.

Key words: winter wheat, nitrogen application rate, plant density, vascular bundle, lodging resistance