Understanding Dormancy

Selecting varieties for short-to long-term storage

Published in the September 2013 Issue Published online: Sep 02, 2013 Nora Olsen, UI extension potato specialist, Tina B
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When describing storability of a potato, the term dormancy is often used. Dormancy length gives insight into how long the potato will store before it initiates sprout development. Knowledge on dormancy length provides information on selecting varieties for short- to long-term storage, planning for proper timing of sprout inhibition products and marketing of the potatoes.

Russet Burbank is known for long-term storage. One reason for this greater storability is the inherent long dormancy of the variety. Interestingly, very few newer varieties or clones evaluated at the University of Idaho Potato Storage Research Facility have shown a similar or longer dormancy than Russet Burbank, except Alpine Russet. Blazer Russet and Clearwater Russet have a shorter dormancy than Russet Burbank and Umatilla Russet, but not as short as Ranger Russet. Although these varieties respond well to chlorpropham (CIPC) applications to limit sprout development, there is a tendency for enhanced storability with longer dormancy varieties.

Table 1 will give you an idea of the relative dormancy length of various currently grown varieties or potential new varieties in development. The table shows a three-year average dormancy length of several russet type varieties. Our definition of dormancy break is when 80 percent of potatoes have at least one sprout =5 mm in length. Typically, peeping of the buds occurs two to four weeks prior to this defined loss of dormancy.

Therefore, depending upon storage temperature, some varieties may need a chlorpropham (CIPC) application soon after the curing period has ended to maximize sprout suppression potential. Other sprout suppression products, such as clove oil or SmartBlock, may be best applied when bud activity is visible. That timing could be predicted from the table provided.

Potatoes stored at lower temperatures tend to have a longer dormancy period compared to potatoes stored at warmer temperatures. This is illustrated in Table 1, where differences in days to dormancy break are observed within a variety as storage temperature is lowered. Ideally, it is best to store potatoes in the lowest temperature possible, yet still maintain the quality of the potatoes for the intended market. This can be more difficult when potatoes are to be processed and sugar levels need to be at a minimum. Just a three-degree difference in temperature equates to approximately a 20-day difference in dormancy break for Russet Burbank (Table 2). The average dormancy length over those 14 years was 180 days at 42 degrees F, 160 days at 45 degrees F, and 140 days at 48 degrees F. This response to various storage temperatures will differ by variety.

Knowing dormancy length of a selected variety will provide options to use the inherent dormancy duration to your advantage for short- and medium-term storage and to properly time sprout inhibition tactics for successful long-term storage. The growing season can impact dormancy length and needs to be factored in to minimize surprises of premature sprouting.

Additional information regarding seed sources, recommended production practices and storage management for these varieties can be found at www.pvmi.org, www.ag.uidaho.edu/potato, http://extension.uidaho.edu/kimberly/tag/potatoes.