Assessing effects of the entomopathogenic fungus Metarhizium brunneum on soil microbial communities in Agriotes spp. biological pest control

Abstract

The release of large quantities of microorganisms to soil for purposes such as pest control or plant growth promotion may affect the indigenous soil microbial communities. In our study, we investigated potential effects of Metarhizium brunneum ART2825 on soil fungi and prokaryota in bulk soil using high-throughput sequencing of ribosomal markers. Different formulations of this strain, and combinations of the fungus with garlic as efficacy-enhancing agent, were tested over 4 months in a pot and a field experiment carried out for biological control of Agriotes spp. in potatoes. A biocontrol effect was observed only in the pot experiment, i.e. the application of FCBK resulted in 77% efficacy. Colony counts combined with genotyping and marker sequence abundance confirmed the successful establishment of the applied strain. Only the formulated applied strain caused small shifts in fungal communities in the pot experiment. Treatment effects were in the same range as the effects caused by barley kernels, the carrier of the FCBK formulation and temporal effects. Garlic treatments and time affected prokaryotic communities. In the field experiment, only spatial differences affected fungal and prokaryotic communities. Our findings suggest that M. brunneum may not adversely affect soil microbial communities.

Ecological arguments to reconsider data requirements regarding the environmental fate of microbial biocontrol agents in the registration procedure in the European Union

“…In contrast, resident communities tend to be not or hardly affected by the application of MBCAs, likely because they are well adapted to the local crop environment and are resilient against introduction of new entomopathogenic microorganisms or antagonists of plant pathogens (e.g. Kröber et al 2014;Mayerhofer et al 2017Mayerhofer et al , 2019Perazzoli et al 2014).…”

Response of soil microbial communities to the application of a formulatedMetarhizium brunneumbiocontrol strain

“…The sequence of internal transcribed spacer region 2 (ITS2) of strain M. brunneum EAMa01/58-Su was determined as described previously (Mayerhofer et al, 2017) using Sanger sequencing with primer pair ITS3 (5 ′ CAHCGATGAAGAACGYRG 3 ′ )/ITS4 (5 ′ TCCTSCGCTTATTGATATGC 3 ′ ) (Tedersoo et al, 2014). The sequence was submitted to NCBI GenBank database (Accession No KY786030; Benson et al, 2015).…”

“…Soil DNA extraction was performed as described by Mayerhofer et al (2017) which included three consecutive DNA extractions from 0.5 g soil of each sample. Soil DNA was dissolved in TE buffer (at 1 ml per 1 g soil dry weight) and subsequently subjected to a clean-up procedure using NucleoSpin® gDNA clean-up kit (Machery-Nagel, Germany).…”

“…The 5 ′ end of the forward and reverse primers were tagged with CS1 and CS2 adapters, respectively, in order to allow multiplexing with the Fluidigm Access Array System (Fluidigm, USA). PCR amplifications were performed as described by Mayerhofer et al (2017). PCRs were conducted in four replicates for each soil sample.…”

“…This approach allows the parallel assessment of many samples and results in tens of thousands of sequences per sample that can be compared to existing databases (Rastogi & Sani, 2011). Cultivation-independent methods have been used to assess potential effects of applied soil fungi used for control of insects, weeds, or nematodes and these studies have revealed no or only transient effects of the applied strains (Hirsch, Galidevara, Strohmeier, Devi, & Reineke, 2013;Mayerhofer et al, 2017;Rousidou et al, 2013;Zimmermann, Musyoki, Cadisch, & Rasche, 2016).…”