Application of Symbiotic Fungi to Reduce the Phytotoxic Effect of Chromium in Lettuce (Lactuca sativa L.) in hydroponic condition

Chromium (Cr) is a toxic metal usually found in many regions and countries, because of excessive discharge of Cr-containing effluents resulting from industrial and agricultural activities. In higher plants, Cr is not essential to plant growth. Exposure to Cr may cause tissue necrosis and limit chlorophyll production. In particular, it is usually involved in electron transfer and induce production of reactive oxygen species (ROS) e.g., hydroxyl radicals and superoxide radicals, resulting in oxidative stresses and damages to plant cells and tissues. Symbiosis fungi significantly accelerate plant growth by improving water and nutrient uptake, early flowering, seed production and greater photosynthetic rate. These fungi change the production of secondary metabolites and enhance adaptation and tolerance to biotic and abiotic stresses. this study aimed to investigate the role of mycorrhizal and endophytic fungi (Glomus intradises and P. indica) as possible tools to reduce the phytotoxicity of Cr.

In order to evaluate the effect of different concentrations of Cr (0, 3 and 15 mg L-1), and symbiotic fungi on growth and physiological properties of lettuce (Lactuca sativa cv. Little Jem), an experiment was carried out as factorial split plot based on Completely randomized design with four replications as soilless system at research greenhouse of University of Mohaghegh Ardabili, in 2021. In this experiment Cr and nitrogen content, root colonization, root and shoot dry weight, leaf number, stem and leaf dry and fresh weight, chlorophyll and carotenoid content, stomatal conductance, electrolyte leakage, ascorbate peroxidase and catalase activities, hydrogen peroxide and were measured.

The results showed that with increasing the concentration of Cr in the symbiotic colonization percentage, nitrogen content, dry weight of roots and shoots, chlorophyll and carotenoid content, stomata conductance and soluble protein decreased. While the content of electrolyte leakage, hydrogen peroxide and ascorbate peroxidase and catalase activity increased. Plants inoculated with symbiotic fungi P. indica and G. intradises were able to reduce the negative effects of Cr toxicity by reducing chromium uptake and increasing nitrogen uptake, root symbiotic percentage, chlorophyll content and activity of ascorbate peroxidase, catalase and hydrogen peroxide.

In general, it is concluded that with increasing the concentration of Cr in the nutrient solution, lettuce growth decreased and the use of symbiotic fungi could improve the morphological characteristics and yield of lettuce under Cr stressKeywords: Mycorrhiza , Soilless system, Chromium, Lettuce