To date, the genome of the potato has not been sequenced because it’s so complex genetically. Chinese researchers are close to solving the puzzle, but until then, the potato must be vegetatively propagated. As an autotetraploid, that makes the spud very susceptible to diseases.
    

For these reasons, Neil Gudmestad, seed potato pathologist, North Dakota State University, advises care in bringing seed potatoes to your farm. In fact, he would not recommend sourcing seed out of province. 
    

“There are more than 150 diseases of potato globally, 40 of which are economically important,” Gudmestad told his audience at the Ontario Potato Conference. “All can be carried either on or in the seed tuber.”

Types of Seed-Borne Pathogen

Type 1 – pathogen carried in the soil adhering to the surface of the potato tuber, Eg. Any soil-borne pathogen such as cyst nematodes, pink rot and Verticillium wilt pathogens 

Type 2 – pathogen carried in seed coat or in periderm (skin) of potato tuber Eg.  Silver scurf and black dot pathogens 

Type 3 – pathogen in seed endosperm or vascular system of propagule tuber Eg. Ring rot bacterium, Dickeya sp

Type 4 – pathogen carried systemically in seed embryo or in all internal tissues of tuber Eg. All potato viruses – PVY, PLRV, potato “Mop top” virus 

Here’s how regulatory agencies treat these pathogens. Type 1 and 2 are either not regulated or if they are regarded as an invasive pathogen – then controlled by quarantine by the Animal and Plant Health Inspection Service (APHIS) or the Canadian Food Inspection Agency (CFIA). Type 3 and 4 pathogens are most commonly regulated through seed certification regulations, occasionally by quarantines.  

Gudmestad understands there are valid reasons to buy out of province, most commonly to access newer varieties. But the risks are huge of either importing a major disease problem, or worse yet, importing a pathogen that can do irreparable harm to your farm. Some of these risks include: powdery scab, bacterial ring rot, cyst nematodes, new strains of potato mop-top virus or Dickeya. Questions remain how APHIS and the CFIA will regulate these new strains of pathogens.

“I personally recommend that potato growers avoid, if at all possible, buying seed from out of province,” says Gudmestad. “If you must buy seed, remember to get a North American Plant Health Certificate in advance of purchase. Ask questions about diseases such as Dickeya, that are not specifically addressed on the certificate.” 

“The risks that you will ‘buy’ a problem that does not exist in your province are higher than you think in this day and age,” he continues. “When in doubt, request a post-harvest test or evaluation by a 
qualified lab.”  

In answering questions from the audience, he indicated that growers should ask for results on sample sizes of at least 400 tubers.  “That’s a good statistical sample size that gives you some assurance you’re down to 0.5 per cent probability of a disease.”