PI-009: Seed Potato Tuber Inspection
Appendix 12: Defects not Scorable
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Excessive moisture before harvest is the main cause of this disorder. Normally, lenticels are inconspicuous on tubers but under high moisture conditions they rise about 1/16 inch (1.6 mm) and form numerous whitish protuberances over the tuber surface. If tubers are held in moist atmospheres, these elevated areas remain whitish, but when the tuber dries, they become skin colored, open and somewhat depressed. They make excellent openings for micro-organisms, particularly soft rot bacteria.
Enlarged lenticels are not scored as a defect in seed potatoes unless associated with disease caused by other pathogenic organisms.
Healed Over Flesh
Occasionally, potatoes are harvested without allowing sufficient time for the skins to set. As a result, the skin of affected potatoes may be damaged and through time will heal and a second skin will develop. This is sometimes called "healed over flesh".
Affected potatoes will have areas that are either darker or lighter brown than the normal skin color. This could materially or seriously affect the potato's appearance. This type of discolouration usually affects only the skin area and not the flesh portion of the potato or the viability of the eyes of seed potato tubers.
Healed over flesh is not scoreable for seed potatoes.
Scald usually results from a rapid loss of moisture through skinned areas and oxidation of immature potatoes. Frequently, the tissue exposed by feathering that has not healed over is scalded and turns dark. Affected tubers turn green or yellow more readily and may be badly shriveled. Frequently rot develops even where no further change in the surface is apparent. In many cases, the affected area becomes sunken and is usually followed by a wet rot.
Scald is not scored on its own, but may be classified either as soft rot, dry rot, or scored as tubers not firm when applicable.
Hollow heart is a condition brought about by too rapid or too irregular growth. It often occurs during wet seasons in very fertile or heavily irrigated soils. Hollow heart consists of more or less irregular cavities of varying size within the potato and is usually lined with light-brown to brown dead tissue. This defect is usually, but not always found, in large, rough, misshapen potatoes. The potato should be cut lengthwise, parallel to the flat side, to determine the defect. If the potato is not cut lengthwise, the hollow heart may not be detected.
Hollow heart may be associated with other malformations of tubers and shall be culled appropriately. Where tubers appear normal and sound and no breakdown occurs, hollow heart is not scored. However, when hollow heart is associated with decay, it is scored under the appropriate category.
Silver Scurf, caused by Helminthosporium solani, is characterized by a grey, smooth, leathery appearance of the skin and is more noticeable when tubers are wet because of a characteristic silvery sheen. This silvery condition is caused by a fungus that penetrates the tubers through the lenticels and skin. After prolonged storage under warm and moist conditions, the tubers look sooty or smudgy. The disease may spread in storage, especially under high humidity and temperatures.
Silver Scurf is not scored on it own but it is scoreable under Damage when the surface is so badly wrinkled, shriveled, or pitted that it seriously affects the germination quality of the potato. When the underlying flesh is dry or corky and affects more than 10% of the surface area of the tuber, Silver Scurf is scored as dry rot.
The presence of any live larvae or insects should be recorded. Make note if the insects are either live or dead when found.
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