Effect of Two Species of VA Mycorrhiza on Reduction of Cadmium Toxicity in Tomato Plant Under Different Levels of Phosphorus

Recent use of wastewater, some chemical fertilizers, and pesticides at agricultural farms have caused problems such as accumulation of heavy metals in soil and agricultural products. One way to solve this problem is to use biologic methods. In a greenhouse experiment, tomato (C.V..Soltan) was inoculated with two species of VA mycorrhiza (Glomus verciform and Glomus etunicatum) or left uninoculated as control plants in sterilized sand. The plants were then treated with three levels of phosphorus (5,20,40 mg P/kg), and three levels of Cadmium (0.02,1,5 mgCd/L). A factorial RB design was used with four replications. Statistical analysis indicated that the percentage of root length colonized (RLC) was increased significantly but Cd concentrations of root, shoot, and fruit was decreased significantly (P<0.01) with phosphorus. Percentage of (RLC) was decreased significantly and Cd concentration of fruit, root, and shoot increased with increasing cadmium (P<0.01). The main effect of Fungus not only had positive significant effect on percentage of(RLC) and Cd concentration of root, but also had negatively significant effect on Cadmium concentration of fruit and shoot (P<0.01). The effectof (fungus * Cadmium) was significant on percentage of (RLC), (P<0.01) and Cadmium concentration of fruit and shoot (P<0.01). The effect of (Fungus * P) was significant on percentage of (RLC), (P<0.01). The effect of (Cd * P) was significant on Cadmium concentration of fruit and shoot (P<0.01). Correlation analysis between measured parameters indicated that percentage of (RLC) had negative correlation with cadmium concentration of fruit and shoot (P<0.05). Also positive correlation was observed between Cd concentration of fruit with Cd concentration of shoot and root (P<0.01). Cadmium concentration of root positively correlated with Cd concentration of shoot (P<0.01). Considering these results, VA mycorrhiza inocolum may be used on polluted soils to reduce toxicity of heavy metals in plants. Second level of phosphorus, which is 20kg P/ha less than the recommended rate for tomato, can be recommended without any reduction in the quality of fruit or mycorhizal activity in tomato roots, but after farm testing.