"Green" fungicides use plants' natural defenses

Date:03-24-2009

Canadian scientists will present a new class of "green" fungicides March 23 in Salt Lake City, Utah, at the 237th National Meeting of the American Chemical Society. The new fungicides exploit a unique plant defense strategy of disrupting a key chemical-signalling pathway used by the fungi to breakdown a plant's normal defenses. The plants boost their natural defenses and overcome fungal attack, say the researchers, whose study was funded by The Natural Sciences and Engineering Research Council of Canada and the University of Saskatchewan.

The new fungicides — called "paldoxins" -- were developed with sustainable agriculture in mind, replacing conventional pesticides and helping to fight the growing problem of resistance. The new fungicides selectively stop fungi that cause plant diseases without harming other organisms or causing adverse environmental effects, the researchers say. They could be applied like conventional pesticides.

"Conventional fungicides kill constantly," explains study leader Soledade Pedras, Ph.D., a professor of chemistry at the University of Saskatchewan. "Our products only attack the fungus when it's misbehaving or attacking the plant. And for that reason, they're much safer."

Plants have a defense mechanism that involves production of natural chemicals called phytoalexins to kill disease-causing fungi. In fighting back, the fungus releases enzymes that detoxify or destroy the phytoalexin, leaving the plant vulnerable to the fungi's attack. Pedras and her colleagues proposed the development of new anti-fungal agents to block the fungi's destruction of phytoalexins. They termed these new agents paldoxins, short for phytoalexin detoxification inhibitors.

"We found that many fungi couldn't degrade this chemical," says Pedras. "So that's what we used to design synthetic versions that were even stronger than the original."

The researchers now have developed six different synthetic versions of the paldoxins, which Pedras says could be marketed within a few years.