Russet Burbank potato plants have been genetically improved to resist insect attack and damage by Colorado potato beetles (Leptinotarsa decemlineata (Say)) by the insertion of a cryIIIA gene encoding the insect control protein of Bacillus thuringiensis var. tenebrionis. A modified gene that dramatically improved plant expression of this protein was utilized. Its expression in Russet Burbank potato plants resulted in protection from damage by all insect stages in the laboratory and in dramatic levels of protection at multiple field locations. Analysis of these genetically modified potatoes indicated that they conform to the standards for Russet Burbank potatoes in terms of agronomic and quality characteristics including taste.
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.
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