Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 9/22/2011
Publication Date: 10/3/2011
Citation: Shapiro Ilan, D.I., Hotchkiss, M.W., Reilly, C.C. 2011. Making beneficial fungi resistant to fungicides. Pecan Grower. 23(2):16-23.
Interpretive Summary: Unlike phytopathogenic fungi some fungi that are found in pecan orchards are beneficial. These beneficial fungi such as Beauveria bassiana and Metarhizium brunneum are natural control agents of various insect pests including the pecan weevil. However, these fungi can be negatively affected by fungicides, thereby reducing their biocontrol potential. Using artificial selection techniques, we demonstrated that fungicide resistance can be increased in the beneficial fungi. However, in some cases the increased fungicide resistance caused a decrease in other characteristics such as fungal growth or virulence (killing power). We conclude that fungicide resistance can be developed in beneficial fungi, which will facilitate the use of these fungi in orchards that use fungicides, but prior to application the selected beneficial fungi should be screened for inadvertent effects on virulence or growth.
Technical Abstract: Unlike phytopathogenic fungi such as scab and Phytophthora, some fungi that are found in the orchard are beneficial. These beneficial fungi such as Beauveria bassiana and Metarhizium brunneum are natural control agents of various insect pests including the pecan weevil. However, these fungi can be negatively affected by fungicides thereby reducing their biocontrol potential. In a previous study we demonstrated enhanced fungicide resistance in B. bassiana through artificial selection. However, it was not clear if the enhanced resistance was due to improved spore germination or vegetative growth (or both). Additionally, the enhanced resistance has only been demonstrated in B. bassiana, and therefore it is of interest to investigate the potential to enhance resistance in other fungi. Thus, the objectives in this study were to determine the potential to enhance fungicide resistance in M. brunneum through artificial selection, and investigate if selection is based on germination, vegetative growth, or both in B. bassiana and M. brunneum. Increased resistance after selection was observed for all fungicide-fungus combinations on solid and or liquid media. Selection resulted in increased resistance to fenbuconazole (Enable) in both fungi in solid and liquid media; in liquid culture fungicide resistance in B. bassiana was manifested by increased germination and mycelial (vegetative) growth, whereas in M. brunneum fungicide resistance concerned only mycelial growth. Selection for resistance to triphenyltin hydroxide (Supertin) varied in the different media. Selection for fungicide resistance, had negative effects on other beneficial traits when selection pressure was removed, e.g., some selected populations showed decreased germination or growth, relative to their non-selected control populations. Additionally, reduced virulence (killing power) to the greater wax moth 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. brunneum, but prior to use the resulting populations should be screened for inadvertent negative impacts on beneficial traits.