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Graphical abstract Highlights • Skermanella and Serratia spp. were isolated from diseased Sesamia inferens. • LC 50 of Skermanella sp. for Sesamia inferens and Cnaphalocrosis medinalis is low. • Skermanella sp. is pathogenic to Sesamia inferens and Cnaphalocrosis medinalis. Abstract Insect pests in the rice agroecosystem, particularly the leaf folder, Cnaphalocrosis medinalis (Guenee) and stem borer, Sesamia inferens (Walker), cause significant yield losses. These pests are generally managed by farmers by application of insecticides and a few biocontrol agents. As a component of integrated pest management, biocontrol agents play a dynamic role in pest control. Although diverse microbial communities are available in the rice ecosystem, bacterial genera such as Bacillus and Pseudomonas spp. are broadly used as biocontrol agents. Therefore, an attempt was made to identify other effective entomopathogenic bacteria to manage the above mentioned pests. In this study, the two entomopathogenic bacteria isolated from diseased pink stem borer ( S. inferens Walker) larvae collected from rice fields were identified as Skermanella sp. (KX611462) and Serratia sp. (KX761232). The larvicidal activity of these two bacteria was evaluated against third instar larvae of C. medinalis and S. inferens in in vitro assays and on potted rice plants ( Oryza sativa var. TN1). The results of this study demonstrated 50% (LC 50 ) larval mortality of C. medinalis at 2.95 × 103 and 5.88 × 103 colony forming units (CFU) ml−1 for Skermanella sp. and Serratia sp., respectively, under in vitro conditions, 2.57 × 104 and 3.38 × 104 CFU ml−1, respectively, in whole plant assays. Similarly, the LC 50 value for Skermanella sp. was 3.80 × 104 CFU ml−1 and Serratia sp. was 2.29 × 105 CFU ml−1 for S. inferens larvae. Our study reports the larvicidal activity of Skermanella sp. against C. medinalis and S. inferens. [ABSTRACT FROM AUTHOR]

Extensive use of imidacloprid in rice ecosystem may alter dynamics of microorganisms and can change soil biochemical properties. The objective of this study was to assess the effect of imidacloprid on growth and activities of microbes in tropical rice soil ecosystem. Four treatments, namely, recommended dose (at 25 g a.i. ha −1 , RD), double the recommended dose (at 50 g a.i. ha −1 , 2RD), five times the recommended dose (at 125 g a.i. ha −1 , 5RD) & ten times the recommended dose (at 250 g a.i. ha −1 , 10RD) along with control were imposed under controlled condition. Dissipation half lives of imidacloprid in soil were 19.25, 20.38, 21.65 and 33.00 days for RD, 2RD, 5RD and 10RD, respectively. In general bacteria, actinomycetes, fungi and phosphate solubilising bacteria population were disturbed due to imidacloprid application. Changes in diversity indices within bacterial community confirmed that imidacloprid application significantly affected distribution of bacteria. Total soil microbial biomass carbon content was reduced on imidacloprid application. Except dehydrogenase and alkaline phosphatase activities, all other soil enzymes namely, β-glycosidase, fluorescien diacetate hydrolase, acid phosphatase and urease responded negatively to imidacloprid application. The extent of negative effect of imidacloprid depends on dose and exposure time. This study concludes imidacloprid application had transient negative effects on soil microbes. [ABSTRACT FROM AUTHOR]

Application of pesticide in agricultural fields is “unnecessary evil” for non-target microflora and fauna. Hence, to identify the safer pesticide molecules against non-target microbes, a long-term pesticide experiment was initiated at National Rice Research Institute, Cuttack, India. In the present study, the effect of continuous application of chlorpyrifos (0.5 kg ha −1 ) in rice fields on non-target groups of soil microbes and nematodes was studied for seven seasons (four wet and three dry seasons) during 2009–2013. Treatments were arranged in a randomized complete block design with four replications of chlorpyrifos-treated (0.5 kg a.i. ha −1 ) (CT) and untreated control (UT) plots. During seven seasons of experimentation, regular application of chlorpyrifos had no significant effect on population of heterotrophic aerobic, anaerobic, oligotrophic and copiotrophic bacteria in CT compared to UT, whereas, population of asymbiotic aerobic nitrogen fixer, nitrifiers, denitrifiers, gram positive and spore-forming bacteria were significantly reduced by nearly 0.25–2 fold in CT than UT. However, comparatively less deviation in population of actinomycetes, fungi, phosphate solubilizing and sulfur oxidizing bacteria were observed in CT than UT. Significant interactions were found between effects of chlorpyrifos with time in population dynamics of microbes. In plant parasitic nematode species, Meloidogyne graminicola (RRKN) and Hirschmanniella spp. (RRN), were significantly lower (p<0.01) in CT compared to UT after first year onwards. The overall observation of five years data indicated that the RRKN population showed a decreasing trend (R 2 =0.644) whereas RRN showed increasing trend (R 2 =0.932) in CT. The drastic chlorpyrifos dissipation was noticed after 15 days of application from the initial residue of 0.25 mg kg −1 soil, which indicated that chlorpyrifos residue in rice field soil was not persistent and its half-life was found to be 4.02 days. Overall, the present findings revealed that non-target effect of repetitive application of chloropyrifos (0.5 kg ha −1 ) on soil microbes and nematodes was found less under rice-rice cropping system. [ABSTRACT FROM AUTHOR]

Bispyribac sodium is frequently used herbicide in the rice field. Though, it has been targeted to kill rice weeds, but its non-target effect on soil microbes in paddy soil was largely unknown. Therefore, in the present study, an attempt was made to assess the non-target effect of bispyribac sodium on alteration of functional variation of soil microbial community and their correlation with microbial biomass carbon (MBC) and soil enzymes. A microcosm experiment set up was made comprising three treatments viz., control (CON) (without application of bispyribac sodium), recommended dose of bispyribac sodium (35 g ha−1) (BS), and double the dose of BS (70 g ha−1) (DBS). Results indicated that the MBC and soil enzyme activities (dehydrogenase, alkaline phosphatase and urease) in BS and DBS-treated soil were significantly (p < 0.05) declined from 1st to 30th day after application as compared to CON. Counts of heterotrophic bacteria, actinomycetes and fungal population were also decreased in BS and DBS-treated soil. The average well color development (AWCD) values derived from Biolog®ecoplates followed the order of DBS ˂ BS ˂ CON. Shannon index value was high (p ≤ 0.05) in CON compared to soil-treated with BS and DBS. Principal component analysis (PCA) showed a clear distinction of the cluster of treatments between CON, BS and DBS. Biplot analysis and heatmap suggested that carboxylic compounds and amino acids showed positive response towards BS-treated soil, whereas phenolic compounds had positive correlation with DBS-treated soil. PCA analysis indicated that oligotrophs was rich in BS-treated paddy soil, whereas copiotrophs and asymbiotic nitrogen fixers were richer in DBS treatment. Overall, the present study revealed that application of recommended dose of BS and its double dose alter the soil microbial population, enzyme activities and functional microbial diversity in paddy soil. • Effect of bispyribac sodium (BS) on microbial community was analyzed in paddy soil. • BS and double dose of BS (DBS) in paddy soil were harmful to most of the soil microbes. • Shannon and McIntosh indices were observed lower in BS and DBS compared to control (CON). • Carbon-source utilizing soil microbes were altered in BS and DBS compared to CON. • Biplot analysis showed a clear distinction of BS and DBS from untreated paddy soil. [ABSTRACT FROM AUTHOR]

Crop residue management has become more challenging with intensive agricultural operations. Zero tillage and crop residue returns, along with the enhancement of in-situ residue decomposition through microbial intervention, are essential measures for preserving and enhancing soil quality. To address this problem in view of stubble burning, field experiments were conducted in rice-rice (variety Swarna) cropping systems under lowland conditions, wherein the following different residue management practices were adopted viz., conventional cultivation (CC), residue incorporation (RI @ 6 t paddy straw ha−1), residue retention (RR @6 t paddy straw ha−1), and zero tillage (ZT). In this experiment, two microbial products i.e. solid microbial consortium (SMC) at 2.0 kg ha−1) and capsule (10 numbers ha−1), were evaluated in both Rabi (dry) and Kharif (wet) seasons under different residue management practices. The results on soil microbial properties showed that application of either SMC or capsule based formulation could significantly improve the soil organic carbon (SOC) content in ZT (9.51 g/kg), followed by RI (9.36 g/kg), and RR (9.34 g/kg) as compared to CC (7.61 g/kg). There were significant differences in the soil functional properties (AcP, AkP, FDA, and DHA) with microbial interventions across all residue management practices. SOC was significantly positive correlated with cellulase (R 2 = 0.64, p < 0.001), β-glucosidase (R 2 = 0.61, p < 0.001), and laccase (R 2 = 0.66, p < 0.001) activity; however, the regression coefficients varied significantly with microbial intervention. Moreover, the availability of N, P, and K in soil was significantly (p < 0.05) improved under microbial treatments with either RR or RI practices. Among the different methods of residues management practices, RI with microbial intervention registered a consistent yield improvement (8.4–17.8%) compared to conventional practices with microbial intervention. The present findings prove that the application of decomposing microbial consortia for in-situ rice residue management under field conditions significantly enhances soil quality and crop yield compared to conventional practices. • Microbial consortium with urea and micronutrient amendments found optimal for in-situ residue decomposition. • Residue incorporation and residue retention enhances SOC content and grain yield compared to zero tillage across two seasons. • Field trial conclusions suggest microbial consortia application has potential for rapid in-situ rice residue decomposition. [ABSTRACT FROM AUTHOR]