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.
Highlights
Barbary fig, Opuntia ficus-indica, is a cactus species native to Mexico introduced in Brazil at the end of the 19th century
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
Respirometry, density of bacterial population and morphologic and genetic variability of bacteria were evaluated with molecular techniques, using BOX-polymerase chain reactions (PCR) in a completely randomized statistical design
Summary
Opuntia ficus-indica, is a cactus species native to Mexico introduced in Brazil at the end of the 19th century. Under the edaphoclimatic conditions of the semi-arid region in Brazil, this cactus assumes a relevant role within livestock farming, due to its high resistance against drought and high temperatures, allied to its adaptability to low fertility soils. Its high efficiency in the use of water contributes to increase economic feasibility of intermediate and small farm producers of low incomes within the Brazilian semi-arid region (Santos et al, 2013; Ramos et al, 2014). Brazil has the largest Barbary fig planted area in the world, over the last few years, the incidence of the cochineal insect (Dactylopius opuntiae Cockerell) has threated the viability of the main variety of Barbary fig within, where this insect has become the leading pest of this cactus plant (Santos et al, 2013). The compounds used for this purpose are constituted by a great number of molecules with different modes of action and toxicity, and its impact over non-target organisms within the agricultural ecosystem of the Barbary fig was not yet been evaluated
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