Screening Of Upland Cotton Germplasm Resources Tolerant To Low Nitrogen And Evaluation Of Their Nitrogen Efficiency At Seedling Stage

Cotton is an important economic crop in China.At present,the increasing of cotton yield mainly depends on the input of nitrogen fertilizer,which leads to a series of problems such as low nitrogen fertilizer utilization rate,increasing production cost and some environmental pollution.The effective way to solve this problem is to explor the potential of cotton and to cultivate cotton varieties with high nitrogen efficiency.In this study,103 cotton varieties(lines)from 419 core collection were selected as test materials.The seedlings were planted by vermiculite culture and nutrient solution irrigation.Two levels of low nitrogen(1 mmol/L)and normal nitrogen(5 mmol/L)were set up.Eleven traits were measured including shoot biomass,root biomass,root-shoot ratio,plant biomass,shoot nitrogen content,root nitrogen content,shoot nitrogen accumulation,root nitrogen accumulation,plant nitrogen accumulation,nitrogen use efficiency,and soil and chlorophyll content.The screening indexes of cotton genotype nitrogen efficiency were analyzed.Based on principal component analysis and cluster analysis,nitrogen nutrition at seedling stage was evaluated and some resources with nitrogen tolerance and high nitrogen efficiency were screened out.The main results are as follows:1.Under normal nitrogen and low nitrogen conditions,the coefficient of variation of nitrogen use efficiency and chlorophyll content were significantly smaller than other indicators,indicating that the effect of low nitrogen stress on them was limited.Therefore,the shoot biomass,root biomass plant biomass root-shoot ratio,shoot nitrogen content,root nitrogen content,shoot nitrogen accumlation,root nitrogen accumlation,and plant nitrogen accumulation were taken as important index for screening nitrogen efficiency of different cotton varieties.Then,the relative values of each index under different nitrogen supply levels were described and analyzed.Combined with factor analysis,the shoot biomass,root biomass,plant biomass,shoot nitrogen accumulation and plant nitrogen accumulation accounted for a larger proportion of the main components.Therefore,the above five indicators can be used as the main screening index for nitrogen efficiency of different germplasm resources.2.The correlation analysis of five selected indexes showed that except for the significant positive correlation between root biomass and the shoot nitrogen accumulation,and the other indicators were extremely significant positive correlation.The correlation coefficient between relative shoot biomass and relative shoot nitrogen accumulation was 0.932,and the correlation coefficient between relative shoot biomass and plant nitrogen accumulation was 0.909,which reached extremely significant level,indicating that the dry matter accumulation of cotton could be increased by increasing nitrogen accumulation,and then the yield could be increased.3.Factor analysis was carried out on the basis of the low nitrogen tolerance coefficients of 11 indexes,and comprehensive indexes were selected according to the principle that the cumulative contribution rate was more than 85%.The 11 indices were transformed into three independent comprehensive indices by principal component analysis.The D value was obtained by membership function method.According to cluster analysis,the varieties could be divided into four groups when Euclidean distance was 5.0.The first group had the strongest resistance to low nitrogen,with 15 varieties accounting for 14.6%;the second group had 29 varieties,accounting for 28.2%;the third group had poor resistance to low nitrogen,with 45 varieties accounting for 43.7%;the fourth group had the worst resistance to low nitrogen,with 14 varieties accounting for 14.0%.Among them,15 varieties with the strongest tolerance to low nitrogen were Wan 231,Lu 890,FH682,Liao 7334-7728,Xinluzao 36,Zhong85271,Luyuan 343,Wanzao 686,Bu3363,E 4396,Tu71-113,thinner floc H10,Lambright GL-N,ZhongR2058 and 208 H-1.4.Based on scatter plotting of nitrogen efficiency comprehensive values of different cotton varieties under normal nitrogen supply and low nitrogen supply,four genotypes can be classified: low nitrogen and low efficiency normal nitrogen high efficient type(type I),low nitrogen and high efficiency normal nitrogen efficient type(type II),low nitrogen and low efficiency normal nitrogen low efficient type(type III)and low nitrogen and high efficiency normal nitrogen low efficient type(type IV).Among them,19.6% were type I,36.27% were type II,23.53% were type III and 20.59% were type IV.Fifteen varieties with the strongest tolerance to low nitrogen and 14 varieties with the worst tolerance to low nitrogen were selected by cluster analysis.In this study,Wanzao 686,Wan231,Tu71-113 and Xixu H10 were further identified as low nitrogen tolerant and high nitrogen efficiency varieties,while six varieties with low nitrogen sensitivity and low nitrogen efficiency were selected including Shann 689,Xuzhou 1818,GP81,Liaoyanglvrong cotton,Rendong 67-86 and Huazhong 91-23.In conclusion,five main indexes for evaluating nitrogen efficiency of different germplasm resources were screened out in this study,including shoot biomass,root biomass,plant biomass,shoot nitrogen accumlation and plant nitrogen biomass;Relative shoot biomass was positively correlated with relative shoot nitrogen accumulation and relative plant nitrogen accumulation,which indicated that increasing nitrogen accumulation could increase biomass accumulation of cotton;Four cultivars with low nitrogen tolerance and high nitrogen efficiency and six cultivars with low nitrogen sensitivity and low nitrogen efficiency were screened out,which could be used for the analysis of nitrogen efficiency mechanism and breeding in the future.