Thomas Gulya Jr. and Brent Hulke
Abstract: Sclerotinia diseases remain the most significant of all diseases on both oilseed and confection sunflower production in the U.S. In 2007 Sclerotinia stalk rot and head rot affected 30% and 26%, respectively, of fields surveyed in North Dakota, South Dakota, Minnesota, Kansas, Colorado and Texas. Stalk rot and head rot affected 1.3% and 2.7% of the 1.97 million acre U.S. crop, with the greatest incidence and severity in North Dakota, where 52% of the U.S. crop is produced. 2007 was a transition year for the USDA Sunflower Unit with the retirement of our long-time geneticist in January and the hiring of a new geneticist in September. While no major breeding efforts were done during the summer of 2007, there were eight oilseed lines and eight confection genetic stocks released in the fall of 2006. In an effort to identify new sources of stalk rot resistance, a portion of the USDA cultivated sunflower germplasm collection from the Plant Introduction Station (Ames, IA) was tested in one location with artificial inoculation. One-hundred-fifty accessions out of approximately 800 without Sclerotinia data were tested in 2007. Entries in the trial ranged from 0% infection (6 entries) to 80%, with a trial mean of 26% infection. The most resistant entries originated from Russia, Spain, and Yugoslavia and will be retested in multiple inoculated stalk rot trials and head rot trials in 2008 for verification. Concerted efforts will be made in 2008 to evaluate the remaining Plant Introductions for stalk rot, and in subsequent years for head rot, in an effort to identify germplasm with resistance to both diseases. Ninety-five commercial hybrids were evaluated for stalk rot resistance at four locations, all with artificial inoculation, and these same 95 entries were tested by NDSU researchers at Carrington, ND for head rot resistance. Three locations generated usable stalk rot data, and this has been forwarded to NDSU for publication in their annual sunflower bulletin A-652 (http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/a652w.htm). Stalk rot severity, averaged over three locations, ranged from a low of 6% to a high of 63% infection at maturity. Head rot data for commercial hybrids, supplied by the NDSU researchers, helped to identify hybrids possessing good levels of resistance to both head rot and stalk rot.
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