Additional index words. Solanum tuberosum, plant population, plant density, economic return Abstract. 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.
A mutation breeding method was developed to select clones of Lemhi Russet that have resistance to blackspot bruise and low temperature sweetening . Following irradiation with gamma rays from a Cobalt60 source, over 2000 tuber eye pieces were planted directly to the field and tubers from the resulting crop were individually evaluated for blackspot bruise potential . Selection for blackspot bruise resistance continued for five clonal cycles . Selection for low temperature sweetening began in the M 3 and continued for three cycles . Ten clones were selected, eight with significantly (p = 0 .05) better blackspot bruise resistance, and two with increased resistance to low temperature sweetening . The results confirm the possibility for the development of a system to improve single selectable quality characteristics in potatoes .
Mutation breeding was used to produce mutants of the potato breeding selection NDA1725-1 with reduced levels of tuber glycoalkaloids. Excised tuber eye-pieces were exposed to 35 Gy of gamma rays from a *°Co source. In the M,Vi, leaf tissue was screened using high-performance thin layer chromatography and each plant given a relative score based on a subjective rating of band intensity. Tubers were harvested from all plants that produced leaves with relatively low levels of glycoalkaloids. Tuber glycoalkaloids were quantified in the M,V2 and M,V3 using high-performance Uquid chromatography, and 35% and 23% of clones with the lowest glycoalkaloid content were selected for further evaluation in each generation, respectively. In the M,V4, M1V5 and M,V6, selection was based on statistically significant differences between the mutant clones and the controls for glycoalkaloid content, as determined using a gravimetric quantification method, as well as on agronomic and quality characteristics. At the end of six clonal generations three selections exhibited acceptable levels of tuber glycoalkaloids and retained enough of the parent clone's exceptional traits to have potential in the commercial potato chip (crisp) industry.
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