ARS | Publication request: Evaluation of Wild Helianthus Species for Resistance to Sclerotinia Stalk Rot

Submitted to: Proceedings of the International Sclerotinia Workshop
Publication Type: Abstract
Publication Acceptance Date: January 17, 2007
Publication Date: April 2, 2007
Reprint URL: http://www.whitemoldresearch.com/files/042007-02.pdf
Citation: Block, C.C., Gulya Jr, T.J., Marek, L.F. 2007. Evaluation of Wild Helianthus Species for Resistance to Sclerotinia Stalk Rot [abstract]. Proceedings of the International Sclerotinia Workshop.

Technical Abstract: The ultimate goal of this project is to evaluate a broad range of wild Helianthus species for Sclerotinia stalk rot resistance. Wild sunflower germplasm is largely unexplored in terms of Sclerotinia stalk rot resistance, but wild Helianthus species are considerably more difficult to work with in field trials than cultivated sunflowers. Seed dormancy issues prevent direct seeding in the field, and thus seedlings need to be germinated, grown in the greenhouse, and later transplanted to the field. One of our objectives was to develop a reliable greenhouse screening method, so that susceptible material could be eliminated and only the most promising germplasm advanced to field trials. In growth chamber studies, incubation temperature was found to be the most important variable, as even modestly higher temperatures were detrimental to disease development. For example, at 21C, 100% of the plants of a susceptible variety wilted and died at an average of 11 days. At 25C, 40% of the plants had no symptoms, even after 21 days. Temperature was a more critical variable than pot size and shape, soil type, inoculum quantity, and inoculum placement in the pots. Screening efforts will focus on annual diploid Helianthus species in the USDA sunflower germplasm collection, primarily the non-H. annuus taxa, such as H. anomalus, H. argophyllus, H. bolanderi, H. debilis (subspecies debilis, cucumerifolius, silvestris, tardiflorus and vestitus), H. deserticola, H. neglectus, H. niveus (subspecies canescens and tephrodes), H. petiolaris (subspecies fallax and petiolaris), H. porterii, and H. praecox (subspecies hirtus, praecox and runyonii). Our initial screening will focus on accessions known to have resistance to rust and/or downy mildew, as they offer the potential to pyramid resistance to several diseases. This will complement the emphasis in the USDA sunflower breeding program at Fargo, ND on developing germplasm with multiple desirable traits.