Links between Soil Bacteriobiomes and Fungistasis toward Fungi Infecting the Colorado Potato Beetle

Area of Science:

• Soil microbiology
• Insect pathology
• Fungal ecology

Background:

• Soil microorganisms influence entomopathogenic fungi, but their collective effect on fungal growth, survival, and insect infectivity remains poorly understood.
• Fungistasis, the inhibition of fungal growth in soil, is a key factor in the efficacy of entomopathogenic fungi as biocontrol agents.

Purpose of the Study:

• To assess fungistasis toward Metarhizium robertsii and Beauveria bassiana in soils from conventional potato fields and kitchen gardens.
• To determine the relationship between soil bacterial communities, fungistasis levels, and the infectivity of entomopathogenic fungi toward the Colorado potato beetle, Leptinotarsa decemlineata.

Main Methods:

• Agar diffusion assays and bacterial DNA quantification were used to measure fungistasis and bacterial density.
• 16S rDNA metabarcoding analyzed soil bacterial community composition.
• Insect survival assays in inoculated soils evaluated fungal infectivity.

Main Results:

• Kitchen garden soils exhibited stronger fungistasis against M. robertsii and B. bassiana and higher fungal densities compared to conventional field soils.
• Fungistasis levels correlated with bacterial DNA quantity and the abundance of Bacillus, Streptomyces, and certain Proteobacteria, which were more prevalent in kitchen garden soils.
• While highly fungistatic soils showed a trend toward increased Colorado potato beetle mortality from B. bassiana, introducing antagonistic bacilli to sterile soil did not significantly alter fungal infectivity.

Conclusions:

• Entomopathogenic fungi can infect insects in the soil environment even with a diverse and abundant antagonistic bacterial community.
• Soil microbiota, particularly Bacillus and Streptomyces species, contribute to fungistasis, but do not completely prevent entomopathogenic fungal activity against insects.