Lying Dormant

This article appears in the August 2021 issue of Potato Grower.

The inherent dormancy length of a potato variety can be described as its internal clock. Dormancy length provides insight into how long the potato will store in the absence of a sprout inhibitor before sprout development is initiated. The dormancy clock is variety-dependent and is impacted by environmental conditions both in-season and post-harvest. Immediately following harvest, potatoes typically will not sprout even under favorable conditions. Once that period has ended, a potato may or may not sprout depending on environmental conditions. Usually, this is seen where elevated temperatures or some sort of stress will cause a potato to sprout earlier. There is a complex sequence of events, involving a lot of plant hormones and other biochemical reactions, for a potato to break dormancy and for cell division and elongation to occur in order to produce a visible sprout.

Storability, or how well a potato will store, encompasses many characteristics including respiration, weight loss potential, bruise and disease susceptibility, sugar and fry color profile, and cellular stability. An important part of the storability equation is dormancy and sprouting behavior. Initiation of sprouting can negatively impact storability of the crop. Knowing the approximate dormancy length and storage temperature and seasonal response will provide valuable information to fine-tune management of a specific variety to maintain storability.

This knowledge can also be helpful in selecting varieties for short- to long-term storage, planning for proper timing of sprout inhibition products and marketing. For seed growers, it will provide an idea of how aggressive they can expect sprouting to be in storage.

Potato variety demographics are evolving with the consistent introduction of new varieties to the industry. Russet Burbank is known for long-term storage thanks largely to the variety’s inherent long dormancy. Breeders are integrating a multitude of desirable characteristics into new varieties. A program at the University of Idaho Potato Storage Research Facility has evaluated storability characteristics of varieties for 20 years. In our studies, varieties responded well to chlorpropham (CIPC) applications to limit sprout development, but in general, there is a tendency for enhanced storability with longer dormancy varieties.

A summary of the relative dormancy lengths of various currently grown varieties or newer varieties at three-storage temperatures is shown in the table below. The data collates a three-year average dormancy length of several russet varieties in the absence of a sprout inhibitor. Our definition of dormancy break is when 80 percent of potatoes have at least one sprout at least 5 millimeters in length. Typically, peeping of the buds occurs two to four weeks prior to this defined loss of dormancy.

Potatoes stored at lower temperatures tend to have a longer dormancy period compared to potatoes at warmer temperatures. This is illustrated as differences in days to dormancy break are observed within a variety as storage temperature is lowered. Just a three-degree difference in temperature equates to approximately a 20- to 30-day difference in dormancy break for Russet Burbank.

Growing season will also impact dormancy length of a given variety. We documented the approximate dormancy length of Russet Burbank in these trials over 15 years of the project. The seasonal affect can range from 30 to 45 days—plus or minus 10 to 20 days from the average. It is difficult to predict how the growing season will influence dormancy length, but temperature, stress and maturity are considered to play a role in the response.

Knowing dormancy length of a selected variety will provide options to use the inherent dormancy duration to your advantage and to develop properly timed sprout inhibition strategies for successful storage. The impact of growing season on dormancy length should also be considered to minimize surprises of premature sprouting.

Additional information regarding recommended production practices and storage management for some of these varieties can be found at www.uidaho.edu/cals/potatoes and www.pvmi.org.

The following table displays the approximate dormancy length (days after harvest) of russet varieties at three storage temperatures. Dormancy length is defined as 80 percent of potatoes have at least one sprout at least 5 millimeters in length.

* Two years of data to calculate dormancy for the variety

** Fifteen-year average

Nora Olsen is a professor and potato specialist based at the University of Idaho’s Kimberly Research & Extension Center. Rhett Spear is an assistant professor and potato variety development specialist at the UI Aberdeen Research & Extension Center.