Effect the different levels of zinc element in efficiency of Rhizobium leguminosarum bv. Viciae atmosphere nitrogen fixing isolated from Vicia faba and some plant characteristics inoculums with its laboratory and formerly

Environmental pollutants like heavy metals at low concentrations are required for various metabolic activities of microbes including Rhizobia and legume crops on one hand, the excessive metal concentrations on the other hand cause undeniable damage to Rhizobia, legumes and their symbiosis. This study deals with the effect of different levels of zinc element in the efficiency and growth of Rhizobium leguminosarum bv viciae that infect Vicia faba laborator. Symbiotic characteristics of these bacteria and some characteristic of Vicia faba plants were studied by treating them with zinc element under normal conditions. Four isolates of R. leguminosarum bv viciae have been isolated and identified from root nodules of Vicia faba plants. These plants were gathered from different agricultural locations in Baghdad and Diyla provinces. Symbols have been given for each isolate (AN-1,AN-2 AN-3 and AN-4).The viable bacterial count have been measured (Cfu) in the laboratory under the effect of three concentrations of zinc element(0.1, 0.2, 0.3 g/L) through incubation for 48, 72 hours from the beginning of bacterial growth. The results showed significant decrease (P≤0.05) in viable bacterial count for all zinc concentrations that are used compared with control groups. Increasing zinc concentrations leads to decrease. Also, there were differences between isolates since AN-3, AN-4 isolates were the more sensitive for zinc element than other isolates. Vicia faba plants were infected with (AN-1, AN-2, AN-3 and AN-4) isolates. These plants were cultured in soil treated with (0.13, 0.2, 0.52 g /3Kg) concentrations of zinc under normal conditions. Some characteristic of Vicia faba plants were studied; such as the measurement of the length of shoot and root net, measurement of the dry and wet weight of the plants, number of root nodules, percentage of nitrogen and the content of protein in plants. Also the results showed a significant decrease of (P≤0.05) for most plan characteristics that are under study, and an apparent decrease in the nodulation process of the plants in comparision with the control groups. The most negatively affected isolates were (AN-3, AN-4) and then (AN-1, AN-2).