Evaluation of osmotic regulation, total phenol, protein and antioxidant enzymes in four fennel populations under saline treatments using vermicompost

Fennel is a medicinal plant; all of its parts were being used by humans in different ways. This plant is relatively sensitive to salinity. A factorial experiment as a randomized complete block design with three replications at the greenhouse level was executed to investigate the effect of vermicompost on the increase of salinity tolerance in four fennel populations (Mashhad, Urmia, Shiraz, and Bushehr) in the vegetative stage of the plant, emphasizing the evaluation of some osmotic and antioxidant protection indicators. Experimental treatments were designed with four levels of salinity (0, 40, 80, and 120 mM of NaCl) and two levels of vermicompost (0 and 5% v/v). After harvesting, the roots were separated from the stem to analyze the biochemical variables. Salt stress caused a decrease in the total soluble sugar and starch content in the shoot and an increase of those in the root of the studied populations. In addition, under stress conditions, the proline content of shoot and root, total free amino acid, total phenol, and activity of guaiacol peroxidase and catalase were increased in fennel populations, while total soluble protein and anthocyanin content were decreased. Vermicompost treatment increased the content of soluble carbohydrates, soluble protein, free amino acids, proline, total phenol, and anthocyanin, and decreased the activity of guaiacol peroxidase in the shoot, as well as the starch content in the roots of fennel populations under non-stressed and stressed conditions. Despite observing the complexity in the changes of the analyzed indicators which were dependent on the type of population and the dose of stress, our results showed that the application of vermicompost with a concentration of 5% can improve the osmotic and antioxidant protection in the studied populations of fennel under salinity stress.