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Researchers Say New Class of Fungicide Is Safer

(Beyond Pesticides, March 25, 2009) Canadian researchers have discovered a new class of fungicides that can bolster a plant’s natural defenses against fungal attack. Unlike conventional fungicides, researchers say these new anti fungal agents, called paldoxins and based on natural plant chemicals, may prove to be safer, more selective and less likely to fall victim to pests becoming resistant.

In a report presented at the 237th National Meeting of the American Chemical Society on March 23 in Salt Lake City, Utah, researchers at the University of Saskatchewan, Canada, describe their development of six synthetic versions of the new anti-fungal agent, which works to block fungal enzymes that overwhelm plants’ natural defenses. Plant chemicals, called phytoalexins, are responsible for the defense mechanism exhibited by many plants to kill disease-causing fungi. However, many fungi release enzymes that detoxify, or destroy the phytoalexin, leaving the plant vulnerable to the fungi’s attack. The researchers took advantage of this counterattack strategy by developing anti-fungal agents to block the fungi’s destruction of phytoalexins.

Paldoxins are short for phytoalexin detoxification inhibitors. Lead researcher, Soledade Pedras, PhD, and her colleagues discovered these agents after screening broccoli, cauliflower, mustard greens and other plants in the so-called “crucifer family” of leafy vegetables. They discovered the most powerful phytoalexin in a flowering plant called camelina or “false flax.” In laboratory tests, camelina’s phytoalexins blocked detoxifying enzymes produced by a wide variety of fungi.

“We found that many fungi couldn’t degrade this chemical,” says Dr. Pedras. “So that’s what we used to design synthetic versions that were even stronger than the original.” Six different synthetic versions of the paldoxins have been created. The synthetic paldoxins have been successful in laboratory tests on several crucifer plants, including rapeseed plants and mustard greens. Field tests have been planned for other important crop varieties. In the future, a similar strategy will be applied to grasses such as wheat, rye, and oat. These grassy plants tend to be more difficult to protect with fungicides than broccoli and related veggies, the researchers say.

These new fungicides could possibly replace toxic conventional fungicides without the threat of resistance, loss of beneficial organisms or other adverse environmental impacts. Since they work in a unique way, disrupting a key chemical signaling pathway that fungi use to breakdown a plant’s normal defenses, these new materials are more selective, stopping fungi that cause plant diseases without harming other organisms. “Our products only attack the fungus when it’s misbehaving or attacking the plant. And for that reason, they’re much safer,” said Dr. Pedras.

A number of different fungicides have been shown to cause cases of occupational asthma among workers, including the fungicides chlorothalonil, fluazinam, and captafol. Researchers found that these fungicides cause hypersensitivity responses in workers, causing their airways to be highly sensitive and reactive to the inhaled fungicides resulting in wheezing and breathlessness. Others, like ziram and maneb have been linked to Parkinson’s disease and non-Hodgkin’s lymphoma.

Source: Science Daily


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