关键词: 不结球白菜, 盐胁迫, 碱胁迫, 四倍化, 综合评价, 产量校正, 种质筛选

Abstract:

【Objective】This study aimed to clarify the differences in salt-alkali tolerance between diploid and tetraploid non-heading Chinese cabbage with the same genetic background across different salt types and developmental stages, to determine the effects of tetraploidization and its dependence on genetic background, and to identify elite materials combining stress tolerance, yield performance, and breeding potential, thereby providing a basis for germplasm evaluation and ploidy improvement in non-heading Chinese cabbage. 【Method】Fifteen pairs of diploid and tetraploid (2X/4X) non-heading Chinese cabbage with corresponding genetic backgrounds were used as experimental materials. NaCl and NaHCO₃ stresses were applied at the germination and seedling stages, respectively, and NaCl drip-irrigation stress was imposed throughout the whole growth period under field conditions. Concentration gradients of NaCl and NaHCO₃ were established at the germination stage; 450 mmol·L^-1 NaCl and 80 mmol·L^-1 NaHCO₃ were applied at the seedling stage; and 200 mmol·L^-1 NaCl was supplied by drip-irrigation in the field, with soil EC_1:5 monitored to characterize salinity intensity. Germination, morphological, physiological, photosynthetic, and yield-related traits were measured. Salt-tolerance coefficients (STCs) were calculated, and a comprehensive salt-tolerance index (D-value) was obtained using principal component analysis combined with the membership function method. The MGIDI index, Fernandez four-quadrant method, paired t-tests, correlation analysis, and regression analysis were further used to evaluate material tolerance, yield performance, and ploidy effects. 【Result】Salt-alkali tolerance in non-heading Chinese cabbage showed clear salt-type differences and developmental-stage specificity. At the germination stage, NaHCO₃ stress caused stronger overall inhibition than NaCl stress. Treatment with 250 mmol·L^-1 NaCl effectively enlarged differences among materials; under NaHCO₃ stress, 40 mmol·L^-1 was sufficient to reveal material differentiation, whereas 60 mmol·L^-1 produced greater overall dispersion and a wider D-value distribution, making it more suitable for comprehensive evaluation at the germination stage. At the seedling stage, responses to NaCl and NaHCO₃ were not fully consistent, and some materials with advantages at the germination stage showed reduced tolerance at the seedling stage, indicating that germination-stage results can not directly substitute for evaluations at the seedling stage or throughout the whole growth period under field conditions. In the field evaluation, D-value rankings were largely consistent with MGIDI rankings (Spearman ρ=-0.775, P=4.87×10^-7), demonstrating good robustness of the multi-trait D-value evaluation. However, Fernandez yield correction showed that most materials with high D-values did not fall into the high-yield and stress-tolerant Group A, suggesting that high comprehensive tolerance does not necessarily indicate high yield under salt stress. The ploidy effect was strongly condition-dependent. Only under NaHCO₃ stress at the germination stage did 4X materials show significantly higher D values than 2X materials (ΔD=0.149±0.164, P=0.004), whereas no significant difference between 4X and 2X was observed under the other four conditions. Pooled analysis across the five conditions showed a significant negative correlation between ΔD and diploid tolerance D_2X (r=-0.601, P=1.15×10^-8), suggesting that the gain from tetraploidization tended to occur in genetic backgrounds with weaker diploid tolerance. After field yield correction, LXRC 2X, PPQ 4X, and L060 2X combined favorable comprehensive salt tolerance with good potential yield and stress yield. 【Conclusion】Salt-alkali tolerance in non-heading Chinese cabbage is jointly regulated by salt type, developmental stage, and genetic background, and tetraploidization does not consistently improve tolerance. A stepwise evaluation strategy integrating preliminary screening at the germination stage, rescreening at the seedling stage, and validation throughout the whole growth period under field conditions, together with yield correction, can improve both screening efficiency and the accuracy of breeding-oriented selection.

Key words: non-heading Chinese cabbage (Brassica rapa ssp. chinensis), salt stress, alkali stress, tetraploidization, comprehensive evaluation, yield correction, germplasm screening