IN THE PAST 10 YEARS, 12 new russet varieties have been released by the Tri State (Idaho, Oregon and Washington) breeding program. Each new cultivar possesses unique characteristics that may make them useful for fresh pack, frozen processing and/or dehydration processing or even for multi-market use. Each variety has its own new set of growth and storage qualities that translate to different management regimes.
An IPC-funded program conducted at the University of Idaho Kimberly Potato Storage Research Facility evaluates the storage characteristics of new varieties. Three recent cultivars released in 2008 include Alpine Russet, Classic Russet and Clearwater Russet.
It is important to be aware of a variety's characteristics and intended market of the crop in order to make wise storage management decisions. Natural dormancy length of a potato variety will be important to know in order to decide if and when sprout inhibitors should be applied. Storage temperature is critical in managing glucose concentrations and fry color quality for process destined potatoes. Information on weight loss and Fusarium dry rot may influence decisions on duration in storage.
ALPINE RUSSET
Alpine Russet (A9305-10) is a high-yielding, medium-to-late maturing cultivar with oblong tubers, light russet skin. This cultivar is well-suited to long-term storage for frozen processing use. On average, Alpine Russet has a dormancy length of 185 days at 42°F, 165 days at 45° and 140 days at 48° (nearly equivalent to Russet Burbank).
Three-year averages indicate that Alpine Russet has a slightly higher susceptibility to Fusarium dry rot than Russet Burbank. Mean dry rot decay (severity) in Alpine Russet was 19 percent compared to 10 percent for Russet Burbank. Percent incidence (rot > 0 percent) was slightly higher in Alpine Russet, at 67 percent versus 55 percent for Russet Burbank.
Total percent weight loss in Alpine Russet was not significantly different than Russet Burbank at 42 or 45°; however, at 48°, it was significantly higher. Glucose concentrations were lower than Russet Burbank across years, temperatures and dates in storage. Figure 1 shows glucose concentrations for Alpine, Classic and Clearwater compared to RB in the 2006-07 growing season. Peak glucose concentration in Alpine Russet occurred at about 180 days after harvest in 2006-07 at 0.12 percent fresh weight (FW). In two of the three years, glucose concentrations remained below 0.10 percent, (which is often considered maximum acceptability by processors) at 42°, in all three years and near or below 0.05 percent at 45 and 48° storage temperatures.
Sucrose concentrations were higher in Alpine Russet at all temperatures and years compared to Russet Burbank. Figure 2 shows percent reflectance and USDA fry color of four varieties in one storage season at three storage temperatures. Fry color was less than or equal to a USDA 1 when stored at both 45 and 48°. At 42°, fry color was USDA 2 or less, except in 06-07, between 70 and 180 days after harvest when fry color reached a USDA 3. Mottling, a dark, uneven coloration which can occur in fried products, scored at a mild level at 42°, and mild to none at 45 and 48°.
CLASSIC RUSSET
Classic Russet (A95109-1) is an early to mid-season russet variety that produces high yields and a high percentage of U.S. No. 1 tubers. Although it is not quite as early as Russet Norkotah, it has the ability to bulk more rapidly than Norkotah, producing large tubers relatively early in the growing season. It has attractive tubers and excellent culinary quality, which makes it very suitable for the fresh-pack industry and it can also be used as an early processor. Classic Russet has a shorter dormancy length than Russet Burbank (20-45 days shorter depending on temperature and year).
Fusarium dry rot results indicate that this cultivar is similar in susceptibility to Russet Burbank and thus classified as moderately resistant. Weight loss during extended storage was significantly higher than Russet Burbank at all temperatures. On average, Classic Russet potatoes had 57 percent higher total (nine-month storage) weight loss than Russet Burbank. Glucose concentrations at 42° in Classic Russet increase steadily in storage and reach a maximum at approximately 150-180 days after harvest (DAH) of 0.15-0.20 percent fresh weight (FW), depending on the year.
At both 45° and 48°, glucose increases at a much lower rate than at 42°. Maximum concentrations were below 0.10 percent and occurred approximately 130 DAH in all years. Overall, glucose and sucrose profiles over the three storage seasons were similar to Russet Burbank.
CLEARWATER RUSSET
Clearwater Russet (AOA95154-1) is a mid-late maturing variety with oblong medium-heavy russeted tubers. Clearwater Russet produces a high percentage of U.S. No. 1 tubers. Tubers of Clearwater Russet exhibit excellent fry color out of storage, and the attractiveness makes them suitable for both processing and fresh market usage.
Clearwater Russet has high specific gravity and is resistant to sugar ends. External and internal defects are minimal for Clearwater even in stressed conditions. The dormancy of Clearwater Russet is relatively short-about 60 days shorter than Russet Burbank. At 48°, Clearwater Russet has a dormancy of 85 days, 90 days at 45° and 110 days at 42°.
Clearwater Russet is classified as having a high Fusarium dry rot potential. In three years of disease testing, means were 31 percent decay (severity) and 63 percent incidence compared to 12 percent decay and 39 percent incidence for Russet Burbank. Weight loss was higher in Clearwater Russet than Russet Burbank at 42 degrees (7.7 percent and 4.9 percent, respectively).
At both 45 and 48 degrees, there were no significant differences between the cultivars in the three-year means, and values were 5-6 percent for the total weight loss in both cultivars. Percent glucose in storage in Clearwater Russet was very low, <0.05 percent fresh weight (FW) at 42 and <0.03 percent FW at 45 and 48 degrees. Percent sucrose was similar in Clearwater Russet to Russet Burbank. Stem-end fry color remained at less than or equal to USDA 1 throughout the nine-month storage period at the three temperatures in three storage seasons. Mottling, a dark, uneven coloration which can occur in fried products, scored at a mild level at 42°, and mild to none at 45 and 48°.
For more information, visit the UI Idaho Center for Potato Research and Education (ICPRE) website (www.cals.uidaho.edu/potato) and the Potato Variety Management Institute (PVMI) website, at www.pvmi.org.
Publications on Storage Management of Umatilla Russet, Gem Russet, Alturas, Summit Russet, Western Russet and A93157-6LS (Premier Russet) can be downloaded free of charge on the web at: www.kimberly.uidaho.edu/potatoes/info.htm or info.ag.uidaho.edu/catalog.