Changes to Soil Microbiome Resulting from Synergetic Effects of Fungistatic Compounds Pyrimethanil and Fluopyram in Lowbush Blueberry Agriculture, with Nine Fungicide Products Tested

Abstract

Lowbush blueberries (Vaccinium spp.) are a crop of economic significance to Atlantic Canada, Quebec, and Maine. The fruit is produced by the management of naturally occurring plant populations. The plants have an intimate relationship with the soil microbiome and depend on it for their health and productivity. Fungicides are an important tool in combatting disease pressure but pose a potential risk to soil health. In this study, amplicon sequencing was used to determine the effects of six fungistatic compounds both alone and in combination via nine commercially available fungicide products on the bacterial and fungal microbiomes associated with lowbush blueberries and to study whether these effects are reflected in crop outcomes and plant phenotypes. One fungicide, Luna Tranquility, a combination of fluopyram and pyrimethanil, was found to impart significant effects to fungal and bacterial community structure, fungal taxonomic abundances, and bacterial functions relative to control. The two fungicides which contained fluopyram and pyrimethanil as single ingredients (Velum Prime and Scala, respectively) did not induce significant changes in any of these regards. These results suggest the possibility that these microbiome changes are the result of the synergistic effect of fluopyram and pyrimethanil on soil microbiomes. While these results suggest a significant disruption to the soil microbiome, no corresponding changes to crop development and outcomes were noted. Ultimately, the majority of the fungicides analysed in this trial did not produce significant changes to the soil microbiome relative to the untreated group (UTG). However, one of the fungicide treatments, Luna Tranquility, did produce significant changes to the soil ecosystem that could have longer-term effects on soil health and its future use may merit additional investigation onto its ecotoxicological properties.

Ranking environmental and edaphic attributes driving soil microbial community structure and activity with special attention to spatial and temporal scales

“…Before release for field use, these chemicals are subjected to systematic evaluations for their potential nontarget effects on biota, including responses of microorganisms in terrestrial and aquatic environments, especially when applied at recommended doses. However, there are reports of nontarget changes in soil microbial composition and function from the use of some pesticides (e.g., herbicides, fungicides, and insecticides), in particular from repeated application, application of chemical mixes, and due to the development of resistance 93 , 94 , 95 , 96 . For example, the effects of commonly used herbicide glyphosate were initially considered minimal, with limited consequences to overall microbiome composition and function.…”

Why Do We Need Alternative Methods for Fungal Disease Management in Plants?

“…For instance, the application of fungicides to mango leaves has been demonstrated to eliminate many endophytes, creating a window of opportunity for pathogens to colonize the tissues formerly that the endophytes formerly inhabited [23]. While this phenomenon has been most readily observed in foliar spray treatments, fungicidal seed treatments have also been associated with similar reductions in beneficial endophytes, and the negative consequences of fungicides on soil microbial communities are well documented [24][25][26][27][28]. Indeed, mounting evidence suggests that seeds protected with systemic fungicides may negatively impact plant health and vigour by targeting beneficial endophytes in the absence of pathogen pressure, the practice may be counterproductive [21].…”

Why Do We Need Alternative Methods for Fungal Disease Management in Plants?

“…For instance, the application of fungicides to mango leaves has been demonstrated to eliminate many endophytes, creating a window of opportunity for pathogens to colonize the tissues formerly that the endophytes formerly inhabited [23]. While this phenomenon has been most readily observed in foliar spray treatments, fungicidal seed treatments have also been associated with similar reductions in beneficial endophytes, and the negative consequences of fungicides on soil microbial communities are well documented [24][25][26][27][28]. Indeed, mounting evidence suggests that seeds protected with systemic fungicides may negatively impact plant health and vigour by targeting beneficial endophytes in the absence of pathogen pressure, the practice may actually be counterproductive [21].…”