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Hotboxing Home-Saved Seed Potatoes

Once-grown home-saved seed has the potential to reduce seed costs, but this should not be at the expense of seed quality.  Poor quality seed often produces a crop of diseased tubers that have a low market value at harvest or lose their value as disease levels increase during storage. Seed potatoes can carry a number of diseases, which may result in uneven emergence, produce gaps in the crop and increase stem, foliage and tuber diseases, all of which can reduce crop yield and quality.
In a good sample there should be no more than two percent rots and at least 98 percent of tubers are expected to produce strong sprouts. A sub-sample of tubers should then be washed and the skin assessed for the incidence and severity of skin blemishing diseases. The most commonly found diseases are silver scurf, black scurf and to a lesser extent skin spot. Seed infected with silver scurf increases the risk of disease transmission to the developing crop, while black scurf and skin spot can infect the eyes on seed tubers thus reducing sprouting ability. Where silver scurf or skin spot is present on five percent of tubers or black scurf is present on any tuber then a fungicide application prior to planting should be beneficial in protecting the ware crop.

Protocol for hotboxing

  1. Collect a representative sample of 100 tubers from each batch to be tested, lifting 10 tubers at random from 10 boxes or 20 tubers from five boxes.
  2. The hot box should consist of a tote box lined with damp kitchen paper on which the tubers are placed.  Place the box in a black plastic bag with it’s open end folded over (not sealed tight)  and store in a warm place (ideally at 15 degrees C).
  3. After seven days examine the tubers for disease symptoms (skin blemishing diseases and tuber rots including blight, soft rot and gangrene).  The number of tubers with disease symptoms should be recorded.
  4. Place the tubers back in the box and return to warm conditions for a further seven days and assess diseases as before.  Additionally 25 tubers should be peeled to assess the level of bruising and then sectioned to detect internal defects.