Screening Of Low-nitrogen Tolerant Germplasm Of Cucumber And Evaluation Of Its Low Nitrogen Tolerance Indexes

Cucumber（Cucumis sativus L.）is one of the main vegetable crops cultivated in China’s facilities,the production of one-sided pursuit of yield over-application of nitrogen fertilizer phenomenon is serious,excessive nitrogen application not only leads to reduced fertilizer utilization rate and fruit nitrate content exceeds the standard,but also causes environmental pollution and other issues.Under the background of strong advocacy of nitrogen reduction fertilizer,breeding cucumber varieties with strong low nitrogen tolerance provides an effective strategy to solve these problems.The rate of nitrogen uptake and the signal sensitivity of the nitrogen system are important nutritional characteristics that reflect the ability of plants to capture nitrogen.In this study,nitrogen nutrient characteristics such as nitrate nitrogen uptake rate and nitrogen system signal sensitivity of multiple cucumber germplasm materials were first identified.Then,the target germplasm obtained by the screening was evaluated by the low nitrogen tolerance index at the seedling stage.Finally,the field low nitrogen tolerance potential of the target germplasm was evaluated by field yield testing.The findings are as follows:1.In this study,using the ¹⁵N stable isotope tracer technique was first established to measure the nitrate uptake rate of cucumber germplasm.The nitrate uptake rate was then determined by measuring the relative abundance of ¹⁵N absorbed by the root system per unit time;germplasm 47 with a high nitrate uptake rate was screened.The average nitrate uptake rate of all cucumber germplasms was 20.20‰/min with a range of 3.30‰/min and50.27‰/min.The nitrate uptake rate of germplasm 47 was the highest at 50.27‰/min;however,germplasm 52 had the lowest nitrate absorption rate at 3.30‰/min.2.Using the cucumber hydroponic"root division"system established in the early stages of the research group to identify the nitrogen system signal sensitivity of multiple cucumber sequencing germplasms;germplasm 47 was more sensitive to the heterogeneous nutrient environment with uneven distribution of nitrate nitrogen.While the heterotrophic nutrient environment in which germplasm 23 was unevenly distributed against nitrate nitrogen was more sluggish,the ratio of the root length on the low nitrogen side to the root length on the high nitrogen side was 0.37,which was 0.23 lower than that of the control9930.The heterogeneous environment with uneven nitrogen distribution was more sluggish,and the ratio of the root length on the low nitrogen side to the root length on the high nitrogen side was 0.92,which was 0.32 higher than that of the control 9930.3.Using sequencing germplasm 9930 as control,the above-mentioned screened germplasm materials 47 and 23 were identified for their low-nitrogen tolerance at the seedling stage.The ability of low nitrogen tolerance at the seedling stage was preliminarily explored by evaluating its morphological and physiological indicators,and then further field yield measurement experiments were carried out,and the results showed that germplasm 47 and 23 were more tolerant of low nitrogen and low nitrogen tolerant germplasm in terms of single fruit weight and yield per plant.