TOLERANCE AND UTILIZATION PATTERN OF PADDY FIELD BACTERIAL ISOLATES TO COMBINATION HERBICIDE FORMULATION —2,4— D AND ANILOFOS (ONESHOT)J. PRABHA, R. GOWRISANKAR, R. PALANIAPPAN AND S. RAMESHAbstract A paddy field exposed to herbicide formulation consisting of combination of 2 chemicals viz., (2, 4-D and anilofos—Oneshot) was screened for its heterotrophic and herbicide resistant bacterial population. The heterotrophic bacterial population was in the order of 10'CUG.g-1. Herbicide (combination-2, 4-D (32%) and anilofos (24%) resistant bacterial population was 103 CFG.g-'. Herbicide (combination —2, 4-D (32%) and anilofQs (25%) resistant bacterial population was 103 CFU.gl. resistant bacterial population was primarily composed of Gram negative organisms with the predominance of Pseudomonas sp..(50%) followed by Vibrio sp. (30%). Bacteria belonging to the genera of Bacillus and Enterobacter were also recorded in the field soil samples. All the 20 field bacterial isolates exhibited resistance to the herbicide (2, 4-D and anilofos - Oneshot) even at 200 ppm (Al). All these bacterial isolates were further subjected to qualitative plate assay for herbicide utilization potency. Mineral Salt medium was supplemented with the chosen herbicide (2, 4-D and anilofos — Oneshot) at 100 ppm concentration (Al) either as sole carbon or nitrogen source. Most of the field bacterial isolates (85%) were incapable of utilizing the test chemical as the sole carbon source. On the other hand, all except Vibrio sp. SKP 16 were able to utilize the test chemical as the sole nitrogen source. Comparing this data with that of earlier investigations carried out in this laboratory with mono herbicide formulations, a distinct difference in the utilization pattern of 2, 4-D and anilofos is recorded. It could be concluded that herbicides in combination invoke differential metabolic response in the bacterium that may have serious implications on the fate of the chemical molecule.
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