Imported seed bearing new pathogens is a threat to the Canadian potato industry, according to a U.S. researcher.
Neil Gudmestad, a distinguished professor of plant pathology at North Dakota State University, was in Brandon this January to deliver a lecture on the importance of planting locally produced seed at Manitoba Potato Production Days.
“There are valid reasons to buy out-of-state or out-of-province seed, but the most common reason is to access newer varieties,” said Gudmestad. “But the risk of either importing a major disease problem, or worse yet, importing a pathogen that can do irreparable harm, are substantial.”
Among the diseases that can be imported on seed, Gudmestad said, are powdery scab, new strains of late blight, bacterial ring rot, potato mop-top virus, potato cyst nematodes and Dickeya, the pathogen that has Gudmestad sounding the alarm.
Dickeya includes invasive pathogens that are responsible for top wilt, black leg and soft rot in potato. Dickeya pathogens are carried in the seed endosperm or the tuber’s vascular system. Dickeya can cause major damage in potato crops, resulting in the downgrading or rejection of seed potato stocks.
Dickeya species D. dianthicola has been found in fields in the Netherlands since the 1970s. Since the mid-2000s, a more aggressive species, D. solani, has been detected in the Netherlands and throughout Europe. Both species are most virulent in wet conditions and temperatures above 25 C.
According to Gudmestad, D. dianthicola has now been found in numerous U.S. states, including North Dakota and Minnesota and, most recently, in a commercial processing potato field in Ontario.
Spread of Dickeya
Species of Dickeya behave similarly, Gudmestad said, so lessons learned from D. solani’s spread in Europe can be applied to D. dianthicola management in Canada and the U.S.
D. solani has spread area to area through infected seed, said Gudmestad. Spread and infection from tuber to tuber is highly efficient during harvest and tuber handling, but the bacterium is also capable of plant-to-plant spread in the field.
Infected potatoes are themselves highly infectious, with only a very small amount of inoculum needed to spread the disease.
D. solani survives less than three months in soil, said Gudmestad, but can survive on production surfaces, which should be disinfected with standard disinfectants.
Post-harvest testing in Europe has been an important component in containing the spread of Dickeya and mitigating severe losses. In the European Union, testing is standardized at 200 tubers per seed lot.
But the best management strategy of all is prevention. Gudmestad emphasized that it is crucial growers in both the U.S. and Canada avoid buying seed from out of state or out of province, if at all possible.
“The risk that you will ‘buy’ a problem that does not exist in your state, province or farm are higher than you think,” he said. “If you must buy seed, remember to get a North American certified seed potato health certificate in advance of purchase.
“Any pathogen that does not exist on a farm, or in an entire province, can only get there by the movement of potato seed from an area that the disease pathogen exists to an area or farm where they do not exist. Potato seed is the only means by which new pathogens can be spread to areas of Canada or to farms where they have not been previously found,” he said.