Wild yeasts make potent fungicides
An Italian study finds that winemakers could use a natural fungus in place of commercial products to control grape rot. Jeff Glorfeld reports.
In a discovery that could benefit the environment and provide a multimillion-dollar windfall for grape growers the world over, researchers from Italy’s University of Milan have identified a strain of wild yeast that is more effective than fungicides in preventing common grape moulds.
Yeasts are found in abundance on wild grapes. Farmed grapes tend to have a smaller number, but many wine-makers are these days experimenting with using them to ferment their crops.
The Milan study, published in open-access journal Frontiers in Microbiology, investigated the ability of some strains of wild yeast to restrict fungus-growth on the fruits.
"The 'wild' environment represents a huge and largely untapped source of biodiversity, which could provide a reservoir of helpful microbes for pest control," says co-author Ileana Vigentini.
Diseases such as fungal infections cost grape growers many millions of dollars each year, both in lost crops and expensive chemical controls. Meanwhile, many farmers are turning away from chemicals and are looking for more environmentally friendly solutions to disease outbreaks. Plus, many fungi are becoming resistant to chemical solutions, reducing their effectiveness.
These factors have sparked great interest in finding eco-friendly disease-control alternatives.
One possibility is to use natural yeasts -- themselves a type of fungus -- to inhibit damaging fungi in crops. Microbes such as yeasts often compete with one another, and naturally produce substances that kill or diminish their rivals. Up to now, however, researchers have been unable to identify yeasts that are as effective as chemical controls.
In the study, researchers investigated whether yeasts isolated from the skins of wild or farmed grapes could inhibit three common moulds -- Botrytis cinerea, Aspergillus carbonarius (sour rot) and Penicillium expansum (blue mould) -- that can ruin grape crops. Initially they isolated and identified yeasts from a type of wild grape found in Georgia, Italy, Romania and Spain, and from farmed grapes from vineyards in Italy.
From a pool of 231 strains comprising 26 yeast species, they identified 20 strains with the most potent anti-mould effects. Of these, 18 came from yeasts found on wild grapes, suggesting that wild plants could be a promising source of useful microbes.
The researchers found that many of the yeasts release enzymes that can digest mould cell walls, or release substances such as acetic acid or hydrogen sulfide that can kill them.
They then tested the yeasts' ability to stop moulds growing on grapes, and compared their effectiveness with a commercial fungicide.
Six strains, from four yeasts all found on wild grapes showed strong fungicidal effects, and one, Meyerozyma guilliermondii, emerged as being more effective than the chemical alternative in preventing mould growth.
Previous investigations had shown that this strain is hardy and does not interfere with wine fermentation. In 2012, a study also found that it suppressed fungal activity and increased shelf life of bread dough.
Although these initial discoveries are promising, indicating the yeast could be well-suited as a biocontrol agent in vineyards, Ileana Vigentini says outdoor trials are needed to confirm this.
"We plan to test some of these yeast strains as a substitute for chemicals in field trials using grapevines," she says.