As a result of conventional farming practices, many natural habitats have been destroyed, and the plant protection methods employed have not only been thought to cause human health problems, but also contribute to about 30% of greenhouse gas emissions.¬† One of the purposes of organic farming therefore, is to minimize the impact on the environment, by employing methods such as crop rotation, planting pathogen-resistant crops, the use of limited amounts of chemical pesticides, and the use of natural manure instead of synthetic fertilizers.¬† It is still a matter of controversy, however, whether or not organic farming methods actually have beneficial effects on biodiversity and microorganism population structures.
Out of all the Vitis vinifera grape vines throughout the world, the proportions of those that are grown under organic conditions are steadily increasing.¬† What has been a source of contention in organic viticulture is the used of copper for plant protection.¬† In areas near some organically farmed grape vines, there has been high soil contamination of copper, which could potentially harm the plants and animals in that environment, as well as the spread of copper and antibiotic-resistant microbes.
The short study presented today hypothesized that the type of plant protection used in conventional versus organically farmed vineyards would have an impact on the microbial (particularly fungal) community structure.
Leaves, shoots, and undamaged grapes were sampled from Sauvignon Blanc grapes from vineyards in Schlossberg, Austria during the last week before harvest.¬† Half of the vineyards were farmed conventionally, and the other half was farmed organically.
Chemicals used for plant protection in the conventional vineyards were: sulfur, paraffin oil, manganese-zinc ethylene bis(dithiocarbamate), proquinazid, iprovalicarb, folpet, pyrimethanil, mandipropamid, quinoxyfen, chloropyrifosmethyl, boscalid, and cyazofamid.¬† Chemicals used for plant protection in the organic vineyards were: sulfur, copper, Myco-Sin, potassium water glass, Frutogard, and fennel oil.¬† Four replicates for both conventional and organic vineyards were examined.
DNA fingerprinting was performed to identify microorganisms present.¬† Once identified, microorganisms were isolated and plated for further analysis.¬† For all replicates, 18 yeasts and 15 filamentous fungal organisms were isolated and tested for antagonistic activity.
- ¬† ¬† ¬† There were statistically significant differences between microbial fingerprints of conventional versus organically managed plots.
o¬†¬† Fingerprints from organically managed plots were more homogenous and were more similar to each other than conventionally managed plots.
o¬†¬† The most abundant yeast in the conventionally managed plots was S. pararoseus.
o¬†¬† The most abundant yeast in the organically managed plots was A. pullulans.
o¬†¬† Cladosporium sp. and Alternaria tenuissima were common in all plots.
- ¬† ¬† ¬† In organically managed plots, a higher abundance of filamentous fungi and yeasts were isolated.
- ¬† ¬† ¬† Antiphytopathogenic potential (i.e. ability to protect against Botrytis cinerea, as tested in the laboratory) was greater in organically managed plots than conventionally managed plots.
o¬†¬† 33 out of 34 A. pullulans isolates showed antagonistic activities (i.e. protective abilities) against B. cinerea.
- ¬† ¬† ¬† There were no significant differences between organic and conventional plots in regards to bacterial fungal communities (at least in respect to Pseudomonas and Firmicutes bacterial populations).
o¬†¬† Vineyard management has no influence on bacterial communities (again, at least in respect to Pseudomonas and Firmicutes).
The results of this brief study suggest that the yeast A. pullulans plays a key role in explaining the structural and functional differences between organic and conventional farming methods.¬† The authors noted that species in the Aureobasidium genus can utilize inorganic sulfur and can absorb/detoxify copper.¬† This is fascinating since organic viticulture methods use both sulfur and copper in their plant protection strategies, and Aureobasidium pullulans was the most abundant yeast present in organically managed plots.¬† Also, A. pullulans has been shown to be an effective antagonist against several fungal pathogens, by competing for space and nutrients, as well as producing cell wall-degrading enzymes.¬† What is also interesting is that A. pullulan produces several typical flavor components in wine, which would be a beneficial characteristic of organic viticulture.
Overall, the type of vineyard management method for plant protection, specifically conventional versus organic management methods, influences the microbial population of the system.¬† Also, not only was the structure of the community altered, but the function of the community changed as well.¬† Specifically, in organically managed vineyards, the number of antagonist microorganisms was greatly enhanced due to larger populations of A. pullulans, which could potentially act as a biocontrol agent for B. cinerea (though more work would need to be done to confirm this).
In conclusion, knowing the structure and function of microbial communities is critical for developing environmentally friendly alternatives for plant protection in organically managed vineyards.
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Source: ¬†Schmid, F., Moser, G., M√ľller, H., and Berg, G. 2011. Functional and Structural Microbial Diversity in Organic and Conventional Viticulture: Organic Farming Benefits Natural Biocontrol Agents. Applied and Environmental Microbiology 77(6): 2188-2191.
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