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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED PEST MANAGEMENT FOR KEY PESTS OF PECAN AND PEACH

Location: Fruit and Nut Research

Title: Comparative impact of artificial selection for fungicide resistance on Beauveria bassiana and Metarhizium brunncum

Authors
item Shapiro Ilan, David
item Reilly, Charles -
item Hotchkiss, Michael

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2010
Publication Date: February 1, 2011
Citation: Shapiro Ilan, D.I., Reilly, C.C., Hotchkiss, M.W. 2011. Comparative impact of artificial selection for fungicide resistance on Beauveria bassiana and Metarhizium brunncum. Environmental Entomology. 40:59-65.

Interpretive Summary: Chemical fungicides are used to suppress harmful fungal diseases that reduce crop productivity. Certain fungi, however, are beneficial because they can kill insects and are therefore used as environmentally friendly bio-insecticides. Unfortunately, fungicides used to suppress harmful fungi also can negatively affect beneficial fungi. In this study, we determined the potential to select (i.e., breed for) beneficial fungi that are resistant to fungicides and thus could be used to suppress insect pests at the same time that fungicides are sprayed. Our experiments involved two commonly used beneficial fungi: the white muscadine fungus (scientific name = Beauveria bassiana) and the green muscadine fungus (scientific name = Metarhizium anisopliae). We selected for resistance to two fungicides that are commonly used in orchard crops such as pecan; the chemical names are fenbuconizole and triphenyltin hydroxide. Results indicated that both fungi could be selected for resistance to both fungicides. However, in the absence of selection pressure (i.e., when no fungicide is being used), some important traits such as fungal germinatin, growth, or virulence (ability to kill the insect) could be reduced in selected fungal populations compared with normal non-selected fungal populations. Therefore, we conclude that it is possible to use selection to enhance fungicide resistance in the white and green muscardine fungi, but prior to application the resulting populations should be screened for inadvertent negative impacts on beneficial traits.

Technical Abstract: Hypocreales fungi such as Beauveria bassiana and Metarhizium anisopliae can be negatively affected by fungicides thereby reducing their biocontrol potential. The overall goal of this study was to investigate the impact of artificial selection for fungicide resistance on two commercial entomopathogenic fungal strains, B. bassiana (GHA) and M. anisopliae (F52). Specifically, the objectives in this study were to determine the potential to enhance fungicide resistance in M. anisopliae through artificial selection, and investigate if selection is based on germination, vegetative growth, or both, in B. bassiana and M. anisopliae. Selection for resistance to fenbuconazole, and triphenyltin hydroxide was assessed through inhibition evaluations on solid media, and germination and mycelial growth in liquid media. Selection for fungicide resistance was observed for all fungicide-fungus combinations on solid and or liquid media. Selection for resistance to fenbuconazole was observed in both fungi in solid and liquid media; in liquid culture fungicide resistance in B. bassiana was based on increased germination and mycelial growth, whereas in M. anisopliae fungicide resistance was based only on mycelial growth. Selection for resistance to triphenyltin hydroxide varied in the different media. For B. bassiana, triphenyltin hydroxide resistance was enhanced in solid media but not in liquid (in germination or mycelial growth), whereas enhanced resistance of M. anisopliae was detected in both media (similar to fenbuconazole, growth but not germination was improved in the presence of the fungicide). Apparently, fungicide sensitivity and selection potential differ based on the medium and fungal species. Selection for fungicide resistance, inadvertently had negative effects on other beneficial traits when fungicide pressure was removed, e.g., some selected populations showed decreased germination or growth, relative to their non-selected control populations. Additionally, reduced virulence to the greater wax moth, Galleria mellonella, was observed in all fungal populations that were exposed to fungicide resistance regimes. We conclude that it is possible to use genetic selection to enhance fungicide resistance in B. bassiana and M. anisopliae, but prior to use the resulting populations should be screened for inadvertent negative impacts on beneficial traits.

Last Modified: 7/23/2014