'Umatilla Russet∑ and 'Russet Legend∑ Potato Yield and Quality Response to

Additional index words. Solanum tuberosum, soil water potential, evapotranspiration, 'Russet Burbank∑ , 'Shepody∑ , 'Frontier Russet∑ , 'Ranger Russet∑ Abstract. 'Umatilla Russet∑ and 'Russet Legend∑ , two newly released potato (Solanum tuberosum L.) cultivars were compared with four established cultivars ('Russet Bur- bank∑ , 'Shepody∑ , 'Frontier Russet∑ , and 'Ranger Russet∑ ). Potatoes were grown under four, season-long, sprinkler irrigation treatments in three successive years (1992-94) on silt loam soil in eastern Oregon. At each irrigation, the full irrigation treatment received up to the accumulated evapotranspiration (ET c) since the last irrigation. Three deficit irrigation treatments had progressively less water. The new cultivars 'Umatilla Russet∑ and 'Russet Legend∑ performed as well as or better than the other cultivars in the full irrigation treatment, with 'Umatilla Russet∑ showing a higher yield potential at the higher water application rates than 'Russet Legend∑ . All cultivars produced more U.S. No. 1 tubers than 'Russet Burbank∑ , except in 1993, an unusually cool and wet year. 'Russet Legend∑ was the only cultivar showing a tolerance to deficit irrigation. In two out of the three years, 'Russet Legend∑ was as productive of U.S. No. 1 yield over most of the range of applied water as 'Shepody∑ , 'Frontier Russet∑ , and 'Ranger Russet∑ were at the higher end of the applied water range. Chemical names used: 0,0-diethyl S-((ethylthio) methyl) phosphorodithioate (phorate); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); and 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1methyl-ethyl) acetamide (metolachlor). soil water potential could provide the level of precision necessary to successfully deficit irrigate potato. The objective of this research was to com- pare two new cultivars, 'Umatilla Russet∑ and 'Russet Legend∑ , with four commercial pro- cessing cultivars to determine the tuber yield and quality response to deficit irrigation. The commercial cultivars tested were 'Russet Burbank∑ , 'Shepody∑ , 'Frontier Russet∑ , and 'Ranger Russet∑ .