DNA Helps Track Origins Of Growing Blight Problem

November 28, 1997

Using DNA markers as a tracking mechanism, a Simon Fraser University researcher has discovered that British Columbia's escalating blight problem - unique in Canada because it affects both potatoes and tomatoes - most likely originated with the importation of diseased tomatoes from Mexico. Dr. Zamir Punja, director of SFU's centre for pest management, says he was surprised at the results of his DNA study which also highlights the importance of home gardeners routinely getting rid of diseased tomato plants year-round. Caused by fungus, blight appears as large, brown blotches on leaves, stems and fruit causing them eventually to shrivel and die. It spreads through the release of spores. "Tomato plants with blight result in high spore levels and spores can travel up to 20 kilometres to infect both potato and tomato plants," he explains. Punja, who has been studying blight for five years, urges home gardeners to get rid of infected tomato and potato plants by burying or bagging them. "Home garden tomatoes are rarely treated for blight and diseased plants are usually left unattended throughout the summer which leads to high spore levels. Disposing of infected plants will help the potato industry and other home gardeners as well," says Punja. B.C.'s growing blight problem has developed in part because of increasingly wet summers, as well as new aggressive strains of the fungus, according to Punja. "Diseased tomatoes are important, as shown by our study of the DNA markers, because they produce genetically complex strains of blight through sexual recombination," he adds. There are no blight-resistant tomato varieties, although greenhouse tomatoes are unaffected because they are enclosed. Punja says blight has become an increasingly costly agricultural disease in B.C. since 1993 when the province experienced an unusually wet summer. The potato industry alone is worth $40 million a year to the provincial economy. The blight affecting B.C. stems from the same fungal disease which was a major factor in the Irish potato famine of 1845-46. "The underlying principle in all of this is that neither borders, nor distances, can prevent diseases from spreading," he concludes. His research is funded by the B.C. Potato Growers Association and is being conducted in collaboration with the provincial Ministry of Agriculture and University of California researchers.

Simon Fraser University

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