The Effect of Humic Acid Use on Reducing Salt Stress in Purple Basil (Ocimum basilicum L.)

Salt stress is a significant environmental stressor limiting plant development, yield potential and overall plant performance worldwide. Humic acid, a biostimulant agent, encourages plant growth and boosts stress tolerance to against the adverse impacts of salt stress. The current research intends to examine the activity of humic acid application in alleviating the detrimental influence of saltinity in purple basil (Ocimum basilicum L. cv. midnight). To achieve this goal, a completely randomised factorial experiment with three replications was designed. Two different humic acid doses (0 and 1000 mg L-1) and three varying salt treatments (0, 75 and 150 mM NaCl) were administered to the plants. Purple basil plants growth traits (plant height, leaf length, leaf fresh and dry weights), chlorophyll fluorescence (Fv/Fm), electrolyte leakage and photosynthetic pigment (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) levels were identified. Plant height, leaf length, fresh leaf weight, dry leaf weight, chlorophyll fluorescence (Fv/Fm), chlorophyll a and total chlorophyll level declined in salt stressed plants subjected in relative to the control group. Humic acid treatment helped with the elimination of the harmful influence of salinity on these parameters (except leaf length, chlorophyll a and total chlorophyll at 150 mM NaCl concentration). However, chlorophyll b and total carotenoid content in salt-treated plants showed no significant difference at 75 mM NaCl, whereas they decreased considerably at 150 mM NaCl. While the influence of humic acid treatment on chlorophyll b and total carotenoid content was statistically insignificant (p>0.05) at 75 mM NaCl, it was found to have decreasing effect at 150 mM NaCl. Furthermore, electrolyte leakage increased linearly with increasing salinity, while humic acid application only showed an ameliorating effect at 75 mM NaCl concentration. The results of this study showed that humic acid was successful in removing the impact of salt stress in purple basil at 75 mM NaCl.