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Intensive agriculture has resulted in an indiscriminate use of pesticides, which demands in-depth analysis of their impact on indigenous rhizospheric microbial community structure and function. Hence, the objective of the present work was to study the impact of two chemical pesticides (chlorpyrifos and cypermethrin) and one biological pesticide (azadirachtin) at two dosages on the microbial community structure using cultivation-dependent approach and on rhizospheric bacterial communities involved in nitrogen cycle in Vigna radiata rhizosphere through cultivation-independent technique of real-time PCR. Cultivation-dependent study highlighted the adverse effects of both chemical pesticide and biopesticide on rhizospheric bacterial and fungal communities at different plant growth stages. Also, an adverse effect on number of genes and transcripts of nifH (nitrogen fixation); amoA (nitrification); and narG, nirK, and nirS (denitrification) was observed. The results from the present study highlighted two points, firstly that nontarget effects of pesticides are significantly detrimental to soil microflora, and despite being of biological origin, azadirachtin exerted negative impact on rhizospheric microbial community of V. radiata behaving similar to chemical pesticides. Hence, such nontarget effects of chemical pesticide and biopesticide in plants' rhizosphere, which bring out the larger picture in terms of their ecotoxicological effect, demand a proper risk assessment before application of pesticides as agricultural amendments.

With increasing application of pesticides in agriculture, their non-target effects on soil microbial communities are critical to soil health maintenance. The present study aimed to evaluate the effects of chemical pesticides (chlorpyrifos and cypermethrin) and a biological pesticide (azadirachtin) on growth parameters and the rhizospheric bacterial community of Vigna radiata. Qualitative and quantitative analysis by PCR-denaturing gradient gel electrophoresis (DGGE) and q-PCR, respectively, of the 16S rRNA gene and transcript were performed to study the impact of these pesticides on the resident and active rhizospheric bacterial community. While plant parameters were not affected significantly by the pesticides, a shift in the bacterial community structure was observed with an adverse effect on the abundance of 16S rRNA gene and transcripts. Chlorpyrifos showed almost complete degradation toward the end of the experiment. These non-target impacts on soil ecosystems and the fact that the effects of the biopesticide mimic those of chemical pesticides raise serious concerns regarding their application in agriculture., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Highlights: [•] Monitoring of non-target effects of bioinoculants in Cajanus cajan's rhizosphere. [•] Individual as well as combination of bioinoculants employed. [•] Cultivation-dependent and -independent approaches to target microorganisms. [•] Increased abundance of PGPR observed in treated plants. [•] Non-target effects evident by ARISA profiles of treated and control plants. [Copyright &y& Elsevier]

To study the effects of two chemical pesticides (chlorpyrifos and endosulfan), and a bio-pesticide (azadirachtin) on bacterial diversity in rhizospheric soil, a randomized pot experiment was conducted on mung bean ( Vigna radiata) with recommended and higher doses of pesticides. Denaturing gradient gel electrophoresis was used to analyze such effects on both resident and active bacterial communities across two time points. It was observed that higher doses of azadirachtin mimicked the effects of chlorpyrifos on bacterial diversity. Both azadirachtin and chlorpyrifos showed a dose- and time-dependent effect, which was observable only at the RNA level. Endosulfan treatments showed dissimilar profiles compared to control. Most of the bands showed high sequence similarities to known bacterial groups, including many nitrogen-fixing, phosphate-solubilizing, and plant-growth-promoting bacteria. This study indicates that pesticides display non-target effects on active microbial populations that serve important ecosystem functions, thereby emphasizing the need to critically investigate and validate the use of bio-pesticides in agriculture before accepting them as safe alternatives to chemical pesticides. [ABSTRACT FROM AUTHOR]