Biodegradation potentials of soil-borne fungal cultures grown on haloxyfop R methyl ester herbicide medium

Abstract

The heterotrophic and haloxyfop-R methyl ester utilizing fungal counts associated with two top soil samples was determined. Five (5) fungal isolates; Aspergillus niger, Candida sp., Trichoderma sp., Fusarium sp., and Alternaria sp. Were cultured from the soil samples using serial dilution as well as pour plate techniques. These isolates were sub-cultured and screened for their ability to use haloxyfop-R methyl ester as sole source of metabolic energy as well as using the turbidimeteric method. Two of the screened fungal isolates which exhibited maximal optical density (OD) difference values; A. niger and Fusarium sp. Were selected and utilized for the subsequent degradation/shake flask experiment. Growth profile parameters which included; pH, OD, dissolved CO2 and weighed dry fungal biomass were determined during the growth profiling test at a 96 hour interval for 16 days using appropriate methods and equipment. Mean soil pH values were 5.08 ± 0.02 and 4.62 ± 0.02 for samples A and B. The mean total heterotrophic fungal count was 8.7×10³ cfu/g ± 1.5 for A and 1.6 × 10⁴ cfu/g ±1.0 for B. The mean pH value observed for A. niger in the course of the growth profile test ranged from 6.0 ± 8.7 to 7.3 ± 8.0 and 7.3 ± 5.8. The mean OD values observed for A. niger and Fusarium sp. In the course of the shake flask experiment varied from 0.66 ± 7.1 to 1.96 ± 4.5 and 1.62 ± 5.4 to1.99 ± 3.6 respectively. With reference to the detection of mean dissolved CO2 values, utilized as an indirect indicator of herbicide mineralization, the axenic cultured A. niger was the most effective amongst the growth profile fungal cultures.