TITLE:
Evidence of Fungicides Degradation by Rhizobia
AUTHORS:
Hassan Moawad, Wafaa M. Abd El-Rahim, Haitham Shawky, Aziz M. Higazy, Zakaria Y. Daw
KEYWORDS:
Fungicides, Rhizobia, Biodegradation, HPLC Analyses
JOURNAL NAME:
Agricultural Sciences,
Vol.5 No.7,
June
24,
2014
ABSTRACT: Fungicides
which are not easily degradable have the greatest adverse effects on soil
microbes. These pesticides negatively affect the growth and multiplication of
fungi and bacteria and consequently cause the disturbance of the natural soil microbial
balance. In this study two fungicide tolerant isolates of rhizobia; clover
isolate (TA1) and peanut isolate (8) were assessed in their capacity to degrade
Vitavax and Rizolex. The performance of these isolates in fungicides
degradation was tested using the colorimetric assay for Rizolex and the HPLC
analysis for Vitavax to detect the degradation products. Using HPLC analyses,
the control sample showed specific peak indicating the Vitavax presence in the
medium. The specific peak did not change in the control samples throughout the
experiment.With the strainTA1 the specific peak of the Vitavax fungicides
started to reduce as the incubation time goes on. The Vitavax fungicide did not
degrade completely after 240 hours of incubation with rhizobial isolate. The
Rizolex used in this study contained blend of Thiram (active ingredient of
Rizolex) and Tolcofs methyl fungicides in 1:1 ratio. The biodegradation of
Rizolex in the liquid media showed the formation of two new intermediates which
were released into the medium indicating the degradation of the tested
fungicide by peanut rhizobial isolate No. 8 in 48 hrs of incubation 45% of this
compound was degraded. This work shows that the selection of fungicides
tolerant rhizobial strains is important to protect the rhizobial inoculants
from the toxic effect of the pesticides.