Post-harvest Test an Important Tool

A Midwinter reminder

Published in the February 2009 Issue Published online: Feb 28, 2009 Seed Potatoes
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As a seed purchaser, you should request the winter test results for the seed you are considering.

February is the time of the year when many potato producers are busy lining up seed for next summer's crop.

A fair price and the availability of the desired variety are certainly high on any buyer's list but there are some other very important details to keep in mind. Like making sure the seed you are considering for purchase has benefited from a winter test.

The winter or "post-harvest" test produces some of the most important information you can get regarding your potential seed source: the best estimate of how much virus is present in the seed lot.

The summer inspections are also important, but they don't tell the entire story. You might look at the situation this way: the summer test provides an estimate of how much virus was present in the seed lot when it was planted. What it cannot do is provide an estimate of how much "current season" spread may have occurred or, more to the point, how much virus is in the seed lot at the end of the season. It is this amount of virus that will show up in the potatoes you plant.

Most current season virus spread in seed potatoes probably occurs during the later part of the growing season and can result from plant to plant contact (in the case of PVY and some other viruses) or from a late infestation of aphids (PVY, PLRV and other viruses).

This late-season spread is important because the infection occurs too late for the plants to show any symptoms. These plants are not removed from the field because the seed producer can't see them and, in fact, never even knows that they are present. Many of the seed tubers produced from infected plants will also be infected and the amount of virus ultimately present in the seed lot can be quite a lot higher than expected.

Winter test results for the various seed certification agencies across the U.S. should be available shortly, if they aren't already.

As a seed purchaser, you should request the winter test results for the seed you are considering. This information is available from the seed certification agency in the state where you purchased the seed on a form called the "North American Certified Seed Potato Health Certificate."

Not only does this document have both the summer and winter test readings, it also has additional information that you might find valuable, such as whether or not there was any late blight or bacterial ring rot on the farm at any time in the last 10 years.

So, as you go about the business of getting your seed lined up for next season, ask for those winter test results. Obtaining this information could save you a lot of trouble in the long run.

One final note, the Idaho Crop Improvement Association began using ELISA to test all seed lots in the Idaho program for PVY last season and will be doing so from now on. The switch to this practice will ensure that the ICIA winter test results for PVY will be as accurate as is currently possible.

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