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Aims: This study aimed at demonstrating the ability of a mold species, isolated from a rice farm agricultural soil, chronically treated with glyphosate herbicide, to degrade glyphosate and to compare different evaluation methods of biodegradation.
Study Design: A completely randomized design of a factorial experiment was used.
Place and Duration of Study: The study was conducted at the Department of Microbiology, University of Calabar, Nigeria between February and April.
Methodology: Molds were isolated from nine rice agricultural soil samples using potato dextrose agar. The molds were screened for glyphosate degradation using different media to determine their requirement for supplementation or not at all. A completely randomized design of a factorial experiment involving 3 factors at 3 levels each, with three replications, was adopted for glyphosate degradation studies. Degradation was monitored by dehydrogenase activity, carbon dioxide evolution, pH changes, fungal dry weight and residual glyphosate determination. A comparative evaluation of the different methods was made using multivariate statistics.
Results: The mold, identified as Trichoderma asperellum strain JK-28, was incapable of using glyphosate as sole sources of phosphorus and nitrogen and so required nutrient supplementation. Largest significant correlation between dependent variables (P < .001; r = - 779) occurred between dehydrogenase activity and fungal dry weight while the lowest was between residual glyphosate and fungal dry weight. Residual glyphosate and pH had negative correlations with other dependent variables. Principal component analysis extracted only one component with a cumulative variance of 70%. Multivariate analysis of variance (three-way MANOVA) of data, interpreted from the Pillai’s Trace test, was significant at P <.001 for the main, two- and three-way interactions.
Conclusion: Trichoderma asperellum strain JK-28 could degrade glyphosate using it as sole carbon source but with nutrient supplementation. Residual glyphosate determination is recommended as most reliable method for evaluating organic pollutant biodegradation.
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