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Norkotah 8

The Potato Breeding and Selection Program at Colorado State University has developed two new Russet Norkotah selections, Selection 3 and Selection 8 , that have larger, more vigorous vines than the Standard Norkotah, resulting in higher yields and better resiliency during the growing season. These new lines are the result of research and selection initiatives by Dr. David Holm, Potato Breeder at CSU's San Luis Valley.

Recognizing that the small vine size of the Standard Norkotah was making them more susceptible to stress from heat, hail, disease and dry conditions, Dr. Holm set out to identify new selections with larger vines that would better handle the stresses commonly encountered during the growing season. Holm first selected the new lines in 1991. By 1993 they were entered into comparative performance trials at the SLV Research Center. These trials demonstrated that Selection 3 and 8 had more vigorous vine growth, slightly later maturity and higher yields than the Standard Norkotah, due to a longer bulking period. These and other trials have shown that these selections required about 100 lbs. per acre less nitrogen, resulting in a real benefit to growers from reduced input cost and higher yields. Based on these promising results, Selection 3 and Selection 8 have been evaluated by researchers across the west in WCC-27 trials in 1997 and 1998. the 1998 data has not yet been compiled. Results from 1997 WCC-27 trials showed even greater yield advantages than had been demonstrated in the Colorado trials. Selection 3 and 8 also had significantly higher yield of tubers larger than 10 ounce compared to the Standard Norkotah. CSU Research Horticultuaralist, Dr. Susie Thompson-Johns has developed Cultivar Specific Management Strategies for Selection 3 and Selection 8. Her advise to growers is to decrease the amount of nitrogen used on Selection 3 and Selection 8. Applying rates the same as used on Standard Norkotahs, can actually result in a yield or grade penalty. However, when these selections are properly managed growers should seed healthier, more vigorous vines that withstand hail damage, heat stress and some disease pressures better than Standard Norkotahs. Characteristics of the Selection 3 are oblong in shape, russet skin and used as fresh market potatoes. Research trial have repeatedly demonstrated yield potential of 50 to 100 lbs. per acre with 100 lbs. per acre less nitro gen. Apply total fertilizer in the range of : N(210-230#), P(120-200#), K(0-40#) are suitable. Performance of Selection 8 has been maximized with applications in the range: N(160-180#), P (120 - 170#), K(0-40#), Pre-plant N application are critical for the early vine growth necessary to support maximum yields, particularly for standard Russet Norkotah (110-140#). this should be reduced to a range of 80 - 100# for the selections. Sprinkler applied N should be in the range of 90 t0 100# for the standard, 80# for Selection 8. All may benefit from applications at a rate of 7-10# per application, but not exceeding 20# per application. Performance in alkali soil is reduced for the standard. The interval at the maximum ET is approximately 2.5 days. Due to a larger vine, but similar rooting characteristics, producers may prefer to shorten the interval to 2 days and decrease application rates slightly to match ET, in order to avoid moisture stress. The selections may require prolonged irrigation later in the season, when compared to the standard due to slightly later vine maturity, however, once vine senescesnce has begun, water needs must be monitored closely. Producers should strive to avoid late season over watering, since it creates ideal conditions for expression of many diseases such as blackleg, pink ort and leak. The selections may display tuber malformations, skin set problems and deep eyes if irrigation is erratic, temperatures are extremely high, or nitrogen fertility excessive. The selections compete better with weeds than Standard Russet Norkotah. No sensitivities to major potato herbicides have been demonstrated by the standard, or the selections. Standard insect control measures are suitable, however, timing and rotation of pesticides are important due to perseverance by aphids and virus spread. It is especially important to continue applications into late season for the selections since vines remain succulent and green longer than the standard. Three to five fungicide applications may be necessary to control foliar early blight for standard Russet Norkotah. Due to the later maturity, susceptibility to foliar early blight and Verticillium wilt are slightly less for the selections when compared to the standard. Tuber set is light to medium ad high in the hill. Greening may be a problem without proper hill conformation. Tuber bulking occurs in a short interval during early to mid-season at an extremely rapid rate. Russet Norkotah is moderately resistant to blackspot bruise. The selections are somewhat susceptible to growth cracks, deep eyes, misshapen tubers and hollow heart if not appropriately managed. Physiological pigmentation (internal purpling) may appear in tubers of all if proper planting depths, hill conformation ad sound nitrogen fertility management are not adhered to. Average days from planting to vine kill are 95-110.. Unlike Standard Norkotah, vine kill my be required for the selections. Adequate skin set occurs in 14 to 21 days. Tubers may become excessively large late in the season, so close monitoring is warranted by early August. Russet Norkotah is an early maturing cultivar released in 1987 by North Dakota State University (APJ 65:597-604, 1988). Primary use is for the fresh market, and it is particularly suited for baking. It is widely adapted in North America and performs very well in the San Luis Valley. In order to address the weaknesses of standard Russet Norkotah including a high requirement for nitrogen fertility and weak vines, Dr. David Holm began a concerted effort in 1991 to identify superior genotypes able to withstand stress situations more favorably. After several years of evaluation, two lines stood out in offering advantages in reduced nitrogen requirements and in stress situations. Pre-planting considerations: Tubers have medium dormancy. SOme producers have indicated that Selection 3 has slightly longer dormancy than the standard. Whole or cut seed is acceptable, however, cut seed may be preferred as the increased stem number aids in limiting oversized tubers late in the season. Tuber size is also controlled through closer within-row seed spacing. Avoid prolonged warming of seed to minimize excessive sprouting and physiological aging (no more than two weeks at 60 F). Precutting may age seed physiologically, as well, but research in Colorado indicates this may not be a significant problem if proper storage conditions after cutting are utilized. Avoid planting seed in cool soils, since delayed emergence may aggravate Rhizoctonia stem canker and result in reduced fertilizer uptake. Plant 4 - 6 inches deep in a broad, well shaped hill to minimize late season greening. Selection 3 will perform better at the deeper planting depth. Vine maturity of Selection 3 is later by about seven days when compared to the standard. Application for US Plant Variety Protection has been made for the two selection ( Colorado Russet Norkotah Selection 3 - PV#9800256; Colorado Russet Norkotah Selection 8-PV#9800255). Plants emerge quickly with a medium, slightly upright vine and white flowers. Selection 3 vines are medium to large, and more upright than those of the standard or Selection 8. Selection 3 blooms more heavily than the standard and the flowering period is longer. All have a determinate growth habit. Root systems for standard russet norkotah and Selection 8 tend to be shallow and concentrated. Selection 3 has a medium sized root system. The selections are not as susceptible to hail damage as standard russet norkotah, and will demonstrate some recovery following such and event. Tubers have white flesh, are long and blocky with medium to heavy russet skin. Eyes are shallow, numerous and well distributed. Specific gravity levels are medium (1.080). Although not considered a processing cultivar, Russet Norkotah will fry directly from the field. Russet Norkotah an the selections generally have few storage problems. However, leak, pink rot blackleg and silver scurf may become serious when proper field and storage management are not practiced. Russet Norkotah is not considered a long term storage cultivar. Due to a propensity for pressure bruise and blackspot bruise development, consider marketing prior to March 1. A not; some producers feel that they may be able to store Selection 3 slightly longer due to stronger dormancy. Potato early dying, caused by Verticillim dahliae is a problem in some years, but can be easily confused with vine senescence. It is not as prevalent for the selections when compared to the standard. SOil borne diseases such as leak, pink rot and silver scurf can be quite common and serious. Bacterial ring rot symptom expression is erratic and may be difficult to see under some circumstances for Russet Norkotah. Symptoms can be mild and tend to appear only after vines begin senescing (90+ days after planting). Expression for the selections is adequate and similar to the standard. Reaction to PVY infection is mild to latent. Infected plants are difficult to detect early in the growing season, but usually become somewhat more detectable as the plants age. Yield losses due to PVY will be in the 30 - 40% range for individual plants based on research conducted in the Pacific Northwest and in Colorado. Expression of symptoms may be delayed for the selections when excessive N is applied. Toxic seedpiece decay syndrome is characterized by severe plant wilting just prior to tuberization, when the plants are switching form seedpiece nutrition to the root system. Plants appear windburned with dehydrated leaf margins in the upper canopy. A light brown, jelly type rotted mass is all that is left of the seedpiece and brown streaks may be visible in the lower stem. Normally the plant recovers within a couple of weeks. This problem may be present when early season wet conditions are linked with warm weather. Toxic seedpiece decay syndrome is rarely seen in the selections.

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