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

Franco Widmer,Martin Hartmann,Jürg Enkerli,Giselher Grabenweger,Sonja Eckard,Adrian Leuchtmann,Johanna Mayerhofer

doi:10.1093/femsec/fix117

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.

Highlights

Soil is a complex and dynamic environment providing habitats for a tremendous number and diversity of soil microorganisms (Nannipieri et al 2003)
From 18 mycosed A. obscurus cadavers obtained from pots treated with fungus colonized barley kernels (FCBK), fungal capsules (Fcap), fungal spore powder (Fpowd), FCBK + Garlic capsules (Gcap) and Fcap + Gcap 82.4% were infected by the applied strain (Table S1; for information on treatments, see Table 1)
Isolates of the genotype of M. brunneum ART2825 were detected at low frequency (6%) in pots before application and isolated from a larvae from an insecticide clothianidin (Insec)-treated pot and very likely represent natural occurrence of the strain, since the soil used in the pot experiment originated from a field at Agroscope Reckenholz where M. brunneum ART2825 has originally been isolated from an Agriotes obscurus larva (Kolliker, Biasio and Jossi 2011; Eckard et al 2014)

Summary

Introduction

Soil is a complex and dynamic environment providing habitats for a tremendous number and diversity of soil microorganisms (Nannipieri et al 2003). Soil microorganisms provide a wealth of functions They play a central role in nutrient cycling and the formation and maintenance of soil structure, they contribute to plant health and they are involved in the natural regulation of insects, pathogens and weeds (Kennedy 1999). All together these functions are vital for maintaining productivity in agriculture and it is important to understand which abiotic and biotic factors, including agricultural practices, may adversely affect microbial communities. The effects of edaphic factors or anthropogenic activities, such as land use, soil compaction and pesticide applications have been studied (Lauber et al 2013; Hartmann et al 2014; Jacobsen and Hjelmsø 2014)

Methods

Results

Conclusion