Abstract:
Herbicides are chemicals used to kill or control unwanted plants and weeds. They could accumulate in soils at toxic levels to contaminate groundwater when they are leached. The in vitro abilities of seventeen fungi isolated from two agricultural soils to grow on paraquat dichloride and glyphosate was investigated. Analysis of physical parameters of the soil was also carried out. Each fungus was inoculated into the herbicides and incubated at 30ºC for 91 days. Dry weight of the mycelium was obtained and chemical analysis of the culture filtrates before inoculating and after incubation were determined. The soil parameters result showed that the soil supported the growth of fungi which help in degrading these herbicides. The results showed that on day 91th of incubation, species of Trichoderma and Diplodia showed abilities to degrade paraquat dichloride because they produced the greatest mycelia in the medium while Penicillium chrysogenum and Rhizopus sp had reduced degradation impact on the herbicide. Less than 50% of the herbicide (paraquat dichloride) residue was found in culture filtrate of Trichoderma sp. Trichoderma harzianum and Aspergillus sp were also able to utilize glyphosate as growth substrate while Penicillium sp degraded the herbicide minimally because the fungus did not produce any mycelium in the medium. More than 50% of glyphosate was degraded by T. harzianum. When the herbicides were combined, species of Trichoderma harzianum, Aspergillus and Curvularia grew best whereas species of Penicillium, Rhizopus and some Aspergillus were inhibited. The growth of Aspergillus sydowii, Penicillium sp, Stachybotrys sp, Aspergillus terreus was higher in control. Aspergillus sydowii produced largest amount of mycelium in the absence of herbicide (control) than other fungi while Aspergillus fumigatus, Rhizopus microsporus and Mucor sp produced reduced amount of mycelia in the absence of herbicide. This study showed that Trichoderma harzianum and Curvularia lunata could be useful in environment clean-up of soil contamination by these two herbicides.
