Back to basics
The 15-year search for sustainable crop protection

April 24, 2009

By Colleen MacPherson

Soledade Pedras has spent a long time, some 15 years in fact, exploring the basic chemistry that governs the battle between pathogens and plants, and it has all paid off with an exciting breakthrough that could protect field crops grown around the world.

In the simplest terms, what the professor of chemistry and Canada Research Chair in Bio-organic and Agricultural Chemistry has found is what she calls a “green” crop protection agent, a sustainable agricultural product that helps plants stop the fungi that cause various diseases without harming other organisms. Unlike conventional pesticides, the new compounds, called paldoxins, “should not interfere with any other living system,” Pedras said. “They don’t kill. That’s it. Full stop.”

Instead, paldoxins help plants shore up their own defenses against pathogens, building on a natural process that Pedras and a large group of graduate students, research associates and post-doctoral fellows have come to understand in the laboratory setting. For Pedras, the work is a natural extension of her being in Saskatchewan, and at the University of Saskatchewan, and “knowing there is a need to develop sustainable agricultural techniques, new methodologies, new approaches to control plant diseases.”

Here is how paldoxins work. Plants under attack by fungi employ natural defenses but, because fungi evolve very quickly, they can produce a macromolecule, or enzyme, that degrades or breaks down those defenses. In studying the crucifer family of plants (plants with four opposed petals arranged in a cross that include cauliflower, brussels sprouts, turnip and broccoli but also mustard, canola and rapeseed), Pedras and her team found that the wild species of this family produce an additional chemical defense that arrests the degradation caused by the fungal enzyme. By creating a synthetic compound, this defense mechanism can be transferred from the wild species to their cultivated cousins.

What make paldoxins so appealing is that they are very specific to a particular pathogen, lying dormant until that pathogen begins attacking the plant.

“This is no different than what medicinal chemists are doing with antibiotics designed to fight a particular pathogen,” she said. “Just like with pathogens that have developed resistance to a particular antibiotic, we’re seeing resistance in pesticides that were used in the 1980s and 90s.”

What has been missing in the search for alternatives to those conventional pesticides has been the basic chemistry, an understanding of the chemical pathways involved in the “communication” between plants and pathogens, she said. This ongoing battle between plants and disease is something that has intrigued Pedras since she was a child spending summers on her grandmother’s farm in Portugal.

“The thing I remember most was that she had vineyards and in the spring, around Easter time, they would be sulfating the vines. They would apply copper sulfate and my grandmother used to say, ‘Just to prevent…’ The worst for us kids was that we couldn’t eat the grapes for many weeks afterwards.”

Although tempted to follow her father into a medical career, “the only thing I really liked was chemistry and reactions that could explain life processes.” After completing her PhD at the University of Alberta and marrying a Canadian, Pedras came to Saskatoon to do post-doctoral work with the National Research Council. There, she was amazed to find “we didn’t know anything about the fundamental pathogen/plant interactions” in crops vital to the economy of the province.

“Now we’re using the knowledge we get from wild plants, with slight modifications, to make better inhibitors, to improve disease resistance in cultivated crops. And the beauty of it is that we should be able to apply this to many different crops. We can see what the enzyme is degrading and make a chemical compound to stop the degradation.”

While she believes strongly in knowledge being freely available, the paldoxin compounds developed in her lab are currently being patented. To develop a technology that can be transferred to farmers requires a commercial investment, she explained, and commercial investors require patent protection. How soon they come to market, likely in the form of a spray, will depend on the amount of resources invested.

“This is a discovery that only comes after doing fundamental work over many, many years, but it opens up a whole world of possibilities,” adding she would like to turn her attention now to wheat, not only because of its economic importance but “because we don’t know much about the chemistry of wheat.”

For Pedras, the basic lab work will continue in all kinds of new areas, but she worries about the time it all takes. “I always feel there is so much to do that I won’t live long enough to accomplish it all.”