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Stephen L. Love and Asunta Thompson-Johns

Seed piece spacing is an important economic consideration in the production of potatoes (Solanum tuberosum L.). The optimum spacing varies with cultivar and intended market. A study was designed to determine the influence of seed piece spacing on yield, tuber size distribution, net returns, and stem and tuber density of three processing potato cultivars. Seed tubers of cultivars Russet Burbank, Frontier Russet, and Ranger Russet were planted 8, 15, 23, 31, 46, 61, 76, or 91 cm apart at two locations in 1988 and 1989. Total, marketable (U.S. No. 1), and midsize (226–452 g tubers) yield, tuber size distribution, net profits from a representative processing contract, and stem and tuber density (number per meters of row) were determined. All three cultivars achieved highest total yields at the narrowest (8 cm) spacing. Maximum marketable and midsize (226–452 g) yield occurred between 15 and 31 cm, depending on the cultivar. Size distribution shifted from a predominance of small tubers at narrow spacings to a predominance of large tubers at wide spacings, and the rate of shift was cultivar-dependent. `Russet Burbank' showed a broad range of optimal spacing for net returns, with a maximum in the range of 23 to 46 cm. Optima for `Frontier Russet' and `Ranger Russet' were between 15 and 46 cm. Of the four tuber measurements, midsize yield appeared to be best for determining optimum spacing. Marketable yield was also a useful measurement. All three cultivars gave maximum midsize yields at a stem density of 10.5 to 12.1 per meter of row and a tuber density of 23.9 to 24.9 per meter of row. Tuber density showed some promise as a predictor of optimum seed piece spacing for new cultivars.

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Stephen L. Love, Timothy J. Herrman and Asunta Thompson-Johns

Glycoalkaloids are a naturally occurring steroidal alkaloid of potatoes exhibiting human toxicity at levels > 30 mg/100 of tuber fresh weight. It has been documented that genotype and environment have a large impact on tuber levels within a potato crop. The impact on glycoalkaloid content was determined for four management variables including variety grown, N fertilizer rate, storage temperature, and length of storage period. In 1989 and 1990, three varieties (Russet Burbank, Norchip, and Gemchip) were planted in plots with three rates of applied N fertilizer (0, 168, and 336 kgh·m-1). Harvested tubers were stored at 4.4 or 10.0C. Tuber samples were obtained 1 month before harvest, at harvest, and then 3 and 9 months after harvest and analyzed for glycoalkaloid content. All four management variables had a significant (P = 0.05) effect on tuber glycoalkaloid content, but only length of storage period had a greater influence than the natural environmental effect as measured by the difference between years. There were significant year the trial was conducted × N fertilizer rate, year × variety, length of storage × variety, and N rate × variety interactions. The interactions were analyzed and explored.

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Stephen L. Love, Asunta Thompson-Johns and Timothy P. Baker

Eight hundred and fifty-three clones of Russet Burbank and 1012 clones of Lemhi Russet were obtained from Native Plants, Inc. in 1988. The clones were produced via a tissue culture system designed to produce somoclonal variants. Four cycles of selection were completed from 1988-1991. Selection was based on resistance to blackspot bruise, a tuber flesh discoloration caused by condensation of free tyrosine; or the ability to produce light french fry color following cold storage. At the end of the four selection cycles all but six Russet Burbank clones and seven Lemhi Russet clones were eliminated. ANOVA across years was completed for the eleven somaclonal variants and Russet Burbank and Lemhi Russet checks.

Of the Russet Burbank clones, three were significantly (p = .05) more resistant to blackspot bruise and one had significantly better fry color after cold storage. All four clones had significantly reduced yield in comparison to the check clones. Of the Lemhi Russet clones, three were significantly more resistant to blackspot bruise, and four had significantly better fry color than the check clone. Only one of the seven clones (one with superior fry color designated L1908) did not show a significantly lower yield potential.

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Stephen L. Love, Bruce K. Werner, Horia I. Groza and Asunta Thompson-Johns

Nine commercially available true potato seed (TPS) hybrids were compared to four standard clonal cultivars with respect to mean and uniformity of foliar characteristics and tuber traits important to the North American potato industry. The TPS hybrids were planted using second vegetative generation tubers derived originally from botanical seed. Ten plants from each plot were individually evaluated for plant height, vine maturity, early blight symptoms, and verticillium wilt symptoms. Following harvest, yield was determined and the tubers were rated or measured for appearance, shape, specific gravity, and french fry color. The TPS hybrids had mean values for all tuber and foliar traits, except plant height, that were not significantly different from those of one or more of the cultivars; generally, values for the hybrids fell amid those of the cultivars. Two of the hybrids were taller on average than any of the four cultivars. In contrast to the means, trait uniformity of the TPS hybrids was consistently less than for the cultivars. For all foliar traits, except plant height, the TPS hybrids were substantially less uniform than the standard cultivars. For specific gravity and french fry color, two important processing quality traits, the hybrids tended to be less uniform than the cultivars; however, the difference was much less pronounced than for the foliar traits. Four of the hybrids were not significantly less uniform than one or more of the cultivars for french fry color and seven were not less uniform for specific gravity. For many market uses, the TPS hybrids appeared to have the tuber yield and quality characteristics needed to compete with standard clonally propagated cultivars.