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38 POTATO GROWER | SEPTEMBER 2017 Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In DISEASE CONTROL | By Ivan Simko & Kathleen Haynes, USDA-ARS Maturity-adjusted resistance of potato cultivars to Verticillium wilt Finding the Fighters Verticillium wilt of potato, also known as early dying disease, is caused by two soil-borne fungi of Verticillium: V. dahliae and V. albo-atrum. Of the two, V. dahliae is found in most of the U.S., whereas V. albo-atrum is found primarily in the northern U.S. and southern Canada. The fungus is capable of long-term survival in the soil and infects plants through the root system. From there it spreads to the vascular tissue, where it interferes with water and nutrient transport. Disease symptoms on potato leaves include wilting, chlorosis and eventually necrosis. Stems of infected plants show vascular discoloration. Tubers develop necrosis in the vascular tissue, which substantially reduces their quality. Verticillium wilt can also markedly decrease yield. Soil fumigation with methyl bromide can control Verticillium wilt, but this fungicide is being phased out because it depletes the ozone layer. Breeding for improved resistance to Verticillium wilt is highly desirable. No potato cultivars are completely resistant, but some show a fairly high level of partial resistance. Potato growers need more information about partial resistance to identify cultivars suitable for production. Potato breeders need such information to select parental materials to develop resistant cultivars. Cultivar variations in plant maturity can make it difficult to separate out symptoms of the disease from natural senescence. Early-maturing cultivars are generally more susceptible to the disease than late-maturing cultivars. In our study, we evaluated 274 cultivars for their MATURITY UNADJUSTED PARTIAL RESISTANCE (LOWER VALUES INDICATE HIGHER RESISTANCE) 1.0 TO 1.5 Abnaki MaineChip Reddale Russette Snowden 1.6 TO 2.0 Ranger Russet Redskin 2.1 TO 2.5 Russet Burbank LaSoda Shepody 2.6 TO 3.0 Katahdin Norkotah Yukon Gold 3.1 TO 3.5 Red LaSoda Russet Kennebec Russet Legend 3.6 TO 4.0 Gemchip Norgold Russet 4.1 TO 4.5 Kennebec Norland (Dark) Red Red Warba Susceptible Resistant