Abstract

Changes on soil microbial activity may be triggered by different management approaches and the study of the effects of such changes on xenobiotics, of non-target populations, may represent a valuable strategy to evaluate their environmental risk potential. The objective of the present study was to evaluate the effect of Phytosanitary control measures over microbial activity and genetic variability of bacteria in soil cultivated under the forage cactus Opuntia ficus-indica. The experiment was performed at Caetés region in Pernambuco, Brazil. Three days after the application of the xenobiotics (water (control); detergent + sodium hypochlorite; Neem oil; Methomyl and Thiamethoxam + Lambda-cyhalotrin), soil samples (0-20 cm) were collected and transported to laboratory. Respirometry, density of bacterial population and morphologic and genetic variability of bacteria were evaluated with molecular techniques, using BOX-PCR in a completely randomized statistical design. Regarding to respirometry, the amount of CO₂ released from the soil samples was greater within the plots where the insecticide Thiamethoxam + Lambda-cyhalotrin was applied, when compared with control. Soil treatments with only water and water + sodium hypochlorite showed the highest population densities (0.96 and 0.94 × 10² CFU.g^-1, respectively). Concerning to morphological characteristics (color), there was prevalence of white color colonies, with a little visual phenotypic variability. However, the use of molecular techniques revealed high genetic variability among the white colored colonies evaluated, demonstrating the importance of more detailed studies on the effects of xenobiotics on soil microbiota prior to its use of recommendation.

Key words: Respirometry, microbiological indicators, BOX-PCR, ecotoxicology, pesticides.