Tuber Internal Growth Defects: CHILLING
Chilling injury to tubers can occur in the field, in storage or in transit due to exposure to low, NON-freezing temperatures.
Surface injury appears as diffuse brown to black patches. Patches may be slightly shiny and are prone to molds.
Cut through affected surface. If no external appearance, cut through stem end and transversely near stem end.
Affected internal tissue appears smokey-grayish and diffuse similar to early stages of leak. A net necrosis, brown specks, in the vascular ring at the stem end is common ("mahogany browning"). It is similar to leaf roll net necrosis. But, unlike the latter which is scattered in tuber (star burst effect), chilling net necrosis is confined in and around the vascular ring. (Phloem tissue is the most sensitive to chilling.) In severe cases, the specks enlarge and are blackened. Brown streaks into tuber may appear.
When boiled, tubers turn gray to black. Due to the accumulation of glucose, affected tissue turns brown during frying resulting in dark chips and fries.
Only a few hours of exposure to temperatures of 32 to 35oF is needed for chilling injury. The disorder is absent when temperatures are above 38oF. Immature tubers, harvested too soon after vine desiccation, are mostly affected. Chilling impairs and delays wound healing. Poor sprouting occurs with affected seed tubers. Chilling lowers internal quality and reduces storage life. Affected tissue turns sweet due to breakdown of starch storage organelles (vacuoles) and subsequent breakdown of starch to glucose by cellular enzymes. Therefore, affected tubers are not suitable for processing. Affected tubers should not be used for seed because they sprout poorly and there is potential of seed decay in the ground.
Avoid exposure to temperatures below 38oF. There are varietal differences in tolerance to level of coolness and its duration.
- Harvest before soil temperature cools to near freezing.
- Tarp truckloads.
- Store seed and table potatoes at 38-40oF.
- Ventilate to dry out chilled tubers and avoid possible rot.
- Keep storage insulation dry.
- Don't store against an outside wall.