Nitrogen nutrition diagnosis and estimation of seed cotton yield based on critical nitrogen concentration for drip irrigation cotton in Southern Xinjiang, China.

The stability and adaptability of the critical nitrogen concentration in drip-irrigated cotton fields in Southern Xinjiang were investigated by measuring the nitrogen uptake (Nuptake), nitrogen nutrition index (NNI), and accumulated nitrogen deficit (Nand). A two-year field study was conducted using five nitrogen levels (0, 75, 150, 300, and 450 kg·hm-2), with cotton cultivars 'Xinluzhong55' and 'Xinluzhong78' as the test materials. We analyzed the effects of nitrogen addition on plant dry matter (PDM) and critical nitrogen concentration dilution curves (PNCc). The Nuptake, NNI, and Nand models as well as a model of the relationships between NNI, Nand, and the relative seed cotton yield (RY) were established based on the PNCc for both cultivars. The results showed that the PNCc, maximum nitrogen concentration (PNCmax), and minimum nitrogen concentration (PNCmin) dilution models in drip-irrigated cotton showed power function relationships with plant dry matter (PDM), with determination coefficients (R2) of 0.905 and 0.960, 0.919 and 0.950, 0.934 and 0.969 for Xinluzhong55 and Xinluzhong78, respectively. Model validation with independent experimental data showed that the critical nitrogen concentrations in cotton grown under drip-irrigated conditions were simulated satisfactorily. The Xinluzhong55 and Xinluzhong78 1:1 line R2, root mean square error (RMSE) and relative estimation error (RE) of the simulated and observed critical nitrogen concentrations were 0.987, 0.051 g·kg-1, 1.95% and 0.984, 0.044 g·kg-1, 1.91%, respectively, showing good stability and adaptability between the two years. According to the Nuptake, NNI, and Nand model, we concluded that 300 kg·hm-2 was the optimum level of nitrogen application in drip-irrigated cotton in Southern Xinjiang. Based on the fitting results of nitrogen level and seed cotton yield, the theoretical appropriate nitrogen applications for Xinluzhong55 and Xinluzhong78 were 322.7 and 336.4 kg·hm-2, respectively. The R2 of NNI, Nand and RY in different growth stages were greater than 0.900, the NNI, Nand and RY estimation model of seed cotton yield based on 1:1 lines of R2, RMSE, and RE were 0.899-0.989, 0.05-0.13, and 4.1%-9.9% and 0.902-0.981, 0.04-0.12, and 5.1%-9.5%, all of which were highly significant. These results could provide new directions for the evaluation and diagnosis of optimum nitrogen application levels and nitrogen status, as well as the estimation of seed cotton yield in drip-irrigated cotton in Southern Xinjiang.

Association mapping and favourable QTL alleles for fibre quality traits in Upland cotton (Gossypium hirsutum L.).

Improving cotton fibre quality is a major breeding goal for Upland cotton in China.To investigate the genetic mechanisms of fibre quality, a diverse panel of 403 Upland cotton accessions was grown, and the fibre quality traits were measured in six different environments. Genotyping was performed with genomewide simple sequence repeats. A total of 201 markers were polymorphic and generated 394 allele loci, and 403 accessions were arranged into two subgroups using Structure software. Of the marker loci, 18.94% showed significant linkage disequilibrium (P < 0.05). A mixed linear model in association mapping showed that 51 associations were significant between 39 polymorphic loci and five fibre quality traits, according to best linear unbiased prediction, and in at least three of six environments. Of the 39 associated marker loci, 12 were coincident with previous studies. There were 41 typical accessions identified as containing favourable allele loci related to fibre quality traits. The identified favourable QTL alleles and typical accessions for fibre quality are excellent genetic resources for future cotton breeding in China.