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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #181496

Title: TWO NEW "VERTICILLIUM" THREATS TO SUNFLOWER IN NORTH AMERICA

Author
item Gulya Jr, Thomas

Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2004
Publication Date: 3/15/2004
Citation: Gulya Jr, T.J. 2004. Two new "Verticillium" threats to sunflower in North America. Proceedings Sunflower Research Workshop. 26th Sunflower Research Workshop, January 14-15, 2004, Fargo, ND. Available: http://www.sunflowernsa.com/research/research-workshop/documents/Gulya_Verticillium_04.PDF

Interpretive Summary: Symptoms of Verticillium wilt have been noticed with more regularity on both oilseed and confection hybrids, based on results from the annual NSA-sponsored yield and disease survey. Isolations of affected plants have yielded two fungi: a new strain of Verticillium dahliae and Phialophora asteris. The former fungus is able to overcome the single gene used in commercial hybrids for Verticillium resistance, thus necessitating the search for new resistance genes. The latter fungus, unrelated to Verticillium, produces similar symptoms and thus can be confused with Verticillium. The gene for Verticillium resistance does not give resistance to symptoms caused by Phialophora.

Technical Abstract: Commercial oilseed sunflower hybrids, presumed to have resistance to Verticillium dahliae, were observed with symptoms of leaf mottle and wilt in Mentor, Minnesota (MN) in the fall of 2002. Isolations yielded pure cultures of V. dahliae, based on the presence of irregularly shaped microsclerotia (50 to 100u in size) and ellipsoidal conidia borne on verticillate sporangiophores. Three-week old plants of USDA sunflower line HA 372 (susceptible to V. dahliae) and HA 89 (possessing the V-1 gene for V. dahliae resistance)(1) were inoculated by stem injection with a 10subscript6 conidial suspension. Symptoms of leaf mottle appeared on HA 372 and HA 89 within two weeks, and reisolation of V. dahliae completed Koch’s pustules, confirming a new strain of V. dahliae capable of overcoming the V-1 resistance gene. In 2003, additional samples from Fisher, MN and Morden, Manitoba (Canada) of the new strain were confirmed by successful inoculation of HA 89 in greenhouse tests, while samples from six sites in North Dakota and South Dakota produced symptoms only on HA 372. To date, the distribution of the new V. dahliae strain appears to be in northwestern MN and adjacent Manitoba. The new strain also produced leaf mottle symptoms in RHA 340 and HAR-2, two USDA lines known to be resistant to the Argentine strain of V. dahliae.