Integrated evaluation of salt tolerance in cigar tobacco (Nicotiana tabacum L.) varieties for sustainable cultivation in saline environments.

Soil salinity is a serious global threat to agricultural productivity, significantly damaging important crops like cigar tobacco (Nicotiana tabacum L.). Identifying salt-tolerant germplasm and understanding the associated physiological and cellular responses are crucial for sustainable crop improvements. In this study, an integrated screening method was used to assess the salt tolerance of fourteen cigar tobacco varieties under 200 mM NaCl stress. Morphological indicators were transformed into salt stress tolerance coefficients (SSTC), and principal component analysis (PCA), together with a membership function approach, was employed to calculate comprehensive evaluation values (D-values). Based on D-values ranking, QX200 and QX103 were identified as the most salt-tolerant and salt-sensitive varieties, respectively. Under salt stress, QX200 showed smaller reductions than QX103 in shoot length (18.46% vs. 38.74%), root length (12.79% vs. 44.05%), shoot fresh weight (42.99% vs. 61.10%), and total leaf area (20.26% vs. 51.78%). Comparative physiological, biochemical, ultrastructural, and molecular analyses further showed that QX200 maintained better cellular homeostasis through stronger antioxidant defense, osmotic adjustment, ion regulation, and lower oxidative damage. Regression analysis indicated that QX200 restricted the transmission of salt-stress responses, whereas QX103 exhibited stronger stress responses. These findings provide a physiological and cellular basis for salt tolerance in cigar tobacco and support breeding of salt-resilient cultivars.