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Genetic variation in nitrogen-use efficiency and its associated traits in dryland winter wheat (Triticum aestivum L.) cultivars released from the 1940s to the 2010s in Shaanxi Province, China.

BACKGROUND
Improving the nitrogen-use efficiency (NUE) of wheat can help mitigate the problems of poor soil fertility under dryland conditions. We conducted field experiments using three nitrogen fertilization levels (0, 120, and 180 kg ha-1 ) applied to eight dryland wheat cultivars to assess nitrogen-use efficiency and its associated traits.


RESULTS
The grain yield (GY) significantly increased with the improvement in variety, mainly due to a substantial increase in 1000-grain weight and harvest index. Modern wheat varieties have stabilized at an optimal plant height and exhibited improved performance in terms of NUE, partial N productivity, N harvest index, and grain protein content compared with older varieties. The NUE of wheat gradually increased with variety replacement. The net photosynthesis rate of the flag leaves in the filling stage improved with the year of cultivar release; Increasing SPAD values of flag leaves in the flowering and filling stages were observed over time, with the flag leaves of modern varieties showing a high chlorophyll content in the filling stage. Additionally, the principal component analysis showed that the SPAD value, grain number per unit area, transpiration rate, leaf area, and grain protein content positively contributed to the clustering of the N180 and modern cultivars (the 2000s-2010s).


CONCLUSION
Overall, high levels of N application did not significantly improve the NUE of wheat. However, modern wheat varieties can optimize N distribution, increase flag leaf photosynthetic capacity, and improve photosynthesis ability, thus enhancing NUE to achieve high yields under a suitable level of N supply. This article is protected by copyright. All rights reserved.