THERE is an old Chinese curse which says: "May you live in interesting times." The last decade or so has certainly been characterized by case after case of "interesting times" in the North American potato industry. We have seen the rise of new and more tenacious types of the potato late blight fungus and the occurrence of more exotic diseases like potato wart. Now we may be looking at exotic new types of potato virus Y (PVY).

PVY is familiar to all potato producers as the virus responsible for common mosaic. The virus is spread by aphids that don't colonize or even like potatoes, and can be difficult to manage for seed producers, because the virus can't be controlled by insecticides. Our best bet for management is to use certified seed produced under strict guidelines designed to keep the virus to a minimum.

An Exotic Want

Here's where that old curse kicks in and things begin to get interesting. Recently, there have been reports of a different variant of PVY called "PVYn." In this case the "n" stands for "necrosis" (dead tissue), but not in potato.

Instead, it indicates that the virus causes a veinal necrosis symptom in tobacco, a close relative of the potato. Now PVYn is exotic enough to be considered a "regulated" pest in the U.S. and production areas where the disease has been found can be placed under quarantine rules, unless certain conditions are met.

Fortunately, some regulated diseases can be handled by a "management plan." The current PVYn management plan was negotiated by U.S. (Animal and Plant Health Inspection Service) and Canadian (Canadian Food Inspection Agency) regulatory agencies. It provides a road map for the various state and provincial seed certification agencies including rules mandating early detection and removal of seed lots that have PVYn. All states and provinces that produce seed potatoes are now under this management plan and business proceeds almost as usual, in spite of the presence of a regulated pest.

But things could get even more interesting. There also has been reference made to yet another exotic form of PVYn, that being PVYntn. In this case, the "ntn" refers to tuber necrotic strains of PVYn, and these strains of the virus can indeed cause a necrotic ringspot symptom in and on the tubers of some varieties.

Since the early 1980s, the disease has become fairly widespread in Europe and is currently handled under guidelines that include aggressive management of all of the mosaic viruses, including PVY, PVYn, and PVYntn types.

We are currently managing PVYn under an international agreement with Canada, the previously mentioned PVYn management plan. Despite our best efforts, this variant of PVY has gotten into the U.S. and Canada. We still don't know for sure how. If we begin to detect ntn over here, what will our course of action be? Perhaps we should be taking a hard look at what the Europeans and other nations are doing with PVY, PVYn, and PVYntn, to give us some guidelines on how to approach the effective management of this new disease.

In the face of all this "interesting" some might say "accursed" - disease activity, I propose a modern American spin on the old Chinese curse. To all of you in the industry, a blessing: "May you live while potato production is boring."

Nolte is extension seed potato specialist, University of Idaho, Idaho Falls, ID 83402; pnolte@uidaho.edu.

Copyright Meister Publishing Company Jun 2002
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