Effect of herbicide Glyphosate on the microorganisms in tea growing soil

Abstract

The In vitro and In vitro experiments were conducted at the Plant Pathology laboratory and experimental field of Bangladesh Tea Research Institute (BTRI) during 2008-2012. The study was conducted to find out the effect of glyphosate and its influence on microorganism proportions of soil in four dilutions. In laboratory experiment, recommended dilutions of glyphosate was made by mixing the required quantity formulated product into PDA before solidification. A zero concentration was prepared for control. Soils were collected from 5 different marks of tea field areas. In field experiment, initially soil nutrient status of the experimental area was determined with the consideration of pH, percent Organic carbon and Nitrogen, Phosphorus, Potassium, Calcium and Magnesium in PPM. The herbicide glyphosate was applied @ 3.7 liter ha‾1. Soil was collected from the top 0 to 9 cm layers three times at one month interval. Herbicide was applied before flowering and after full ground coverage was obtained. In both cases, for mycofloral analysis serial dilution (10-3, 10-4, 10-5 and 10-6) were same. Colony forming unit g-1 of soil was counted after 4-7 days. Results revealed that the pH of soil was moderately acidic with value of 4.8 ± 0.0254, having only 1.03 ± 0.0483% organic carbon, 0.12 ± 0.0042% total nitrogen, 140.95 ± 0.0275 ppm available phosphorus, 45.45 ± 0.0052 ppm potassium, 97.40 ± 0.0134 ppm calcium and 49.40 ± 0.0037 ppm magnesium. Trichoderma sp was dominated for all the time of observations, accounting more than 20% of total colony count. Glyphosate treated sample only Penicillium and Aspergillus sp were recorded contributed only up to 10% in 10-3 dilution. In 10-4 dilution with control, Phomopsis, Ustulina, Sclerotium, Trichoderma, Rhizoctonia, Penicillium and Aspergillus sp were recorded. Among these seven organisms Trichoderma was dominated for all the time of observations, accounting more than 20% of total colony count. All other organisms were contributing up to 20% identical colony count after two months of herbicide spray. Glyphosate treated sample with same concentration, Sclerotium, Rhizoctonia, Penicillium and Aspergillus sp were recorded contributed only up to 10% while it was up to 20% colony count for the same organisms in 10-5 and 10-6 dilutions from two months of herbicide spraying. Therefore, it was indicated that the glyphosate has toxic effect on Phomopsis and Ustulina as soil mycoflora. In contrast to the fungal suppression, Sclerotium, Trichoderma, Rhizoctonia Penicillium and Aspergillus sp showed enhancement at higher concentration of herbicide.