Effects of uniconazole on Tagetes erecta growth and physiological characteristics under saline alkali stress

We used potted marigold plants (Tagetes erecta) to explore the effects of uniconazole on marigold growth and physiological characteristics under saline-alkali stress. We first determined appropriate concentrations for inducing saline-alkali stress (NaCl ꞉ NaHCO₃ = 1 ꞉ 1, 75 mmol·L⁻¹), then conducted testing with these concentrations. Seven treatment groups, including CK (deionized water sprayed on the leaves), T₁ (saline-alkali stress + 0 mg·L⁻¹ uniconazole solution), T₂ (saline-alkali stress + 25 mg·L⁻¹ uniconazole solution), T₃ (saline-alkali stress + 50 mg·L⁻¹ uniconazole solution), T₄ (saline-alkali stress + 75 mg·L⁻¹ uniconazole solution), T₅ (saline-alkali stress + 100 mg·L⁻¹ uniconazole solution), and T₆ (saline-alkali stress + 125 mg·L⁻¹ uniconazole solution) were established, and growth and physiological indicators were measured. The results were analyzed by correlation and principal component analyses, revealing that during the growth process, aboveground and underground marigold tissues were inhibited upon reaching day 12 of saline-alkali stress via the application of 75 mg·L⁻¹ of exogenous spray. Uniconazole significantly alleviated the attenuation in the aboveground and underground biomass of marigold under saline-alkali stress. Chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll a + b (Chl a + b), and chlorophyll a/b (Chl a/b) all showed downward trends, while malondialdehyde (MDA) content, relative conductivity (REC), peroxidase activity, proline (Pro) content, and soluble sugar (SS) showed upward trends by day 12 of saline-alkali stress. Superoxide dismutase activity first increased, then decreased. The correlation of 10 indicators indicates that Chl a has a significant positive correlation with Chl b, Chl a + b, Chl a/b (P < 0.01) and a significant negative correlation with MDA and REC (P < 0.01). The comprehensive ranking of different concentrations of uniconazole on marigold impact on saline alkali stress was as follows: T₄ > T₃ > T₅ > T₆ > T₂ > T₁. In conclusion, exogenous uniconazole can alleviate the negative impacts of saline-alkali stress on marigold seedlings, enhance their resistance, increase their root activity, and alleviate the inhibition of saline-alkali stress on their growth. 75 mg·L⁻¹ (T₄) exerted the most potent effect.