Seed & Chemical
Harnessing nature’s ability to evolve
November 30, 1999 By Treena Hein
As is the case with many crops, some wild potato species are more resistant to insect pests than modern varieties. “This is mostly because of the natural chemicals found in the leaves,” says Dr. Yvan Pelletier, an entomologist at the Agriculture and Agri-food Canada’s (AAFC’s) Potato Research Centre (PRC) in Fredericton, New Brunswick. “Beetles like the Colorado potato beetle try a bite or a few bites of the leaves of wild species, but then stop because of the noxious taste.”
There is also one wild species, notes Pelletier, where adult beetles are very strongly repelled by the plant’s odour alone. “There’s a volatile compound present that’s a very powerful anti-feedant,” he says.
Scientists have found success elsewhere with harnessing natural repellents, and teams like Pelletier’s are currently building on this success in all corners of the world. The neem plant, for example, contains a compound that has been isolated and is used effectively against foliage-eating insects. The insecticides Rotenone and pyrethroids were both derived from natural plant chemicals, notes Pelletier. “After these natural compounds were isolated, synthetic forms were then created that mimic their action, but provide a greater amount of stability and strength.”
Breeding and chemistry projects
For several years, two projects have been underway to try to harness the power of the natural chemicals in wild potato leaves. A major long-term breeding project is aimed at combining the genetics in a wild variety with modern varieties; it will lead to the eventual creation of a hybrid cross that still possesses repellent compounds in the leaves but also features all the traits needed for commercial cultivation, and adaptations for Canadian growing conditions. This project is currently being carried out by a large group of breeders at PRC, including Dr. Agnes Murphy, Dr. Benoit Bizimungu and Dr. David De Koeyer, along with graduate students and a co-operative of potato breeders in France called Comité Nord des producteurs de plant de pomme de terre.
From the resistant wild potato species, several successive crosses are required to adapt the plant to Canadian conditions and improve the tuber qualities. So far, the Fredericton team has made five backcrosses with one wild species, and a few more might be needed before one selection is good enough to become a variety. For each cross, Pelletier says hundreds of plants are produced and tested for Colorado potato beetle (CPB) resistance, but also for other commercially interesting traits such as cooking or cold sweetening. The material derived from the wild S. oplocense species also has a very good cold-sweetening quality, similar to Russet Burbank.
Ideally, it would also be nice to be able to harvest the leaves as well as the potatoes from these plants, says Pelletier. “We could extract the chemicals to use on other standard varieties that don’t have resistant compounds in their leaves or even use the extracted chemicals on other crops.”
The parallel project involves isolating the repellent chemicals in the leaves of wild potatoes and developing natural pesticides to control CPB or other insects. In this endeavour, Pelletier is joined by PRC colleagues De Koeyer and Dr. Hellen Tai, as well as Dr. Larry Calhoun from the University of New Brunswick in Fredericton, and Dr. Ian Scott at Agriculture and Agri-Food Canada in London, Ontario. “It sounds like an easy task to isolate the compounds, but it’s quite daunting because there are thousands of chemicals in a plant’s leaves,” says Pelletier. The team is analyzing leaves from six wild species native to South America that demonstrate good insect repellency. One of the species looks like modern varieties do, but all the others are smaller, feature different leaflets (but similar flowers), and creep along the ground. “We’ve been growing three of them for 15 years, and we’ve added the other due to suggestions by colleagues at the International Potato Center in Lima, Peru,” says Pelletier.
All along, the team has been surprised by the variety of compounds they have found. “It’s families of compounds that we have to isolate and identify, in order to see their potential, and there are many of them,” Pelletier explains. “The isolation process is done by looking at the spectrum of compounds using a mass spectrophotometer contained in Russet Burbank potatoes and comparing that to what’s in wild ones.”
Team member and bio-chemist Calhoun then works on determining which chemicals are bioactive and stable enough to use. “We are keeping an open mind,” says Pelletier. “We know there is certainly something in there, but it could be that a mixture of compounds is more important than any specific chemical. It’s not an easy task.”
After the team determines and isolates the active chemical, they will create a stable spray, one that will not degrade in warm temperatures and in sunlight. “We’ll then test these compounds,” says Pelletier, “by spraying them on the beetles, just like you would a regular pesticide, and observing the effect. It will be a great accomplishment to get to that stage.”