Symbiotic Effect of Trichoderma atroviride on Growth Characteristics and Yield of two Cultivars of Rapeseed (Brassica napus L.) in a Contaminated Soil Treated with Copper Nitrate

IntroductionAccumulation of heavy metals in agricultural soils can be a threat to crop production due to plant toxicity. In the recent years, hyperaccumulator plants are cultivated to cleaning up the soils which contaminated with pollutants especially heavy metals. However, the biomass of these plants is low and metal specific. Many studies have shown that microorganisms can be used to significantly reduce the toxicity of heavy metals. Therefore, the present study aimed to determine the role of Trichoderma atroviride on the growth characteristics of tow cultivars of rapeseed in different levels on copper.
Materials and MethodsIn this study, a pot experiment was conducted in factorial arrangement based completely randomized design with three replicates. Treatment were T. atroviride fungi at two levels of inoculated and non-inoculated plants, four levels of copper nitrate including 0, 50, 100 and 150 mg l-1 and two cultivars of rapeseed consist of Hayola 401 and Sarigol. Trichoderma atroviride was prepared from Mycology Lab of Sari Agricultural Science and Natural Resource University. PDA medium (potato extract, dextrose and agar) was kept for a week at 25˚C to propagation of fungal strain. The used medium was previously sterilized in autoclave for 30 minutes. So, this fungus propagated in Wheat's bran for five days. Healthy and uniform seeds of rapeseeds were separated from rogues and infertile ones. Seeds disinfected in hypochlorite sodium 0.5% for five minute and then washed with distilled water three times. After preparing fungus spore suspension of 108 CFU per ml water, 50 g wheat' bran mixed to the soil of each pot. Twenty sterilized seeds sown in 2 cm of soil depth in 25×30 cm pot with 10 kg capacity. Copper nitrate was used to pollute treated soil. During this experiment did not used any pesticides and herbicides and all weed controlled manually. Some growth and yield related parameters such as plant height, number of secondary branches, pod number and length of primary and secondary branches, were determined. All statistical analysis were performed using SAS software (version 9.1) and mean comparisons were made by the least significant difference (LSD) test.
Results and DiscussionResults showed that increasing copper content in growth medium markedly decreased pod number in main branches in Hayola 401 while in Sarigol the maximum pod number was recorded at the 50 mg l-1 of copper nitrate. The presence of the Trichoderma, however, increased pod number in branches. Sarigol resulted more pod numbers in branches than Hayola 401 (2.5 times vs. 64%). Also, the maximum pod numbers in branches (about 1.3 fold as compared to the uninoculated control) were observed in Trichoderma inoculated plants which received 100 mg/L of copper nitrate. The maximum plant height in Hayola 401 and Sarigol (0 and 100 mg l-1 of copper nitrate, respectively) recorded when those plants inoculated with Trichoderma. The presence of the Trichoderma in the growth medium significantly improved the pod length of in main branches in Hayola 401 rather than Sarigol.
ConclusionsMany researches showed that rapeseed is a hyperaccumulatore plant for heavy metals such as copper, cadmium, nickel, zinc and lead. On the other hand, many researchers confirmed that soil beneficial microorganisms such as Trichoderma spp. could improve the growth and yield attributes of plant especially in polluted soil. In conclusion, inoculation of rapeseed plants with Trichoderma could enhance the growth characteristics of rapeseed particularly under high levels of copper in the soil. Sarigol, however, respond better than Hayola 401 in terms of yield and yield components. Since, important aspect of bioremediation is inhibition of pollutants passes through a food chain, thus, coexistence of beneficial microorganisms that capable to transform contaminants into nontoxic products are very important.