Submitted to: Proceedings of the International Sclerotinia Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2005
Publication Date: 2/15/2005
Citation: Rashid, K.Y., Seiler, G.J. 2005. Epidemiology and resistance to Sclerotinia head rot in wild sunflower species. Proceedings of the International Sclerotinia Workshop. Sclerotinia Initiative Annual Meeting, January 18-20, 2005, Minneapolis, MN. Available: http://www.whitemoldresearch.com/html/abstractdetails2.cfm?Research_ID=119
Technical Abstract: Field trials were conducted in 2002, 2003, and 2004 to understand the epidemiology of the Sclerotinia infections to wild sunflower heads and stems, to establish methodology for assessing wild sunflower germplasm, and to identify sources of resistance. In 2004, 400 accessions of the perennial wild sunflower species Helianthus maximiliani and H. nuttallii were evaluated using artificial inoculation with a combination of ascospores and ground sclerotinia-infected millet seed. Different groups of plants (5-10) from each accession were inoculated at the early flowering (August 16) and late flowering (August 30) stages, and were covered with light-brown paper bags. A few puffs of water were applied into each covering bag using a hand-held sprayer at the 2nd and 3rd day after inoculation to maintain high humidity and enhance the infection and disease development processes. The level of infection in 2004 was very high in this nursery compared to previous years. The high level of head and mid stem infections was widely spread in all commercial sunflower crops in the region due to the prolonged period of wet and cool weather during the 2004 growing season which created ideal conditions for Sclerotinia infections and development in all susceptible crops. No signs of the typical soft rot and head disintegration as observed in commercial sunflower head rot symptoms were seen in the wild species. The stems were infected and showed typical symptoms of bleaching, shredding, and the formation of tiny cylindrical sclerotia inside the stems, while the heads were shriveled, dry with little or no seed setting. Most wild accessions identified with resistance in 2002-2003 remained resistant in 2004. However, a few accessions showed various levels of susceptibility in 2004 in spite of their resistant reaction in 2002-2003 trials. The combination of ground Sclerotinia-infected millet inoculum and ascospores with a paper bag covering in 2004 resulted in 93% infection in comparison with 88% infection in 2002 and 55% in 2003. Seven accessions remained healthy in the three years of testing under the various artificial inoculation methods. Such accessions are believed to have genetic resistance to Sclerotinia head rot and mid-stem infection. Present research is focusing on studying the genetics of this resistance and the transfer of the resistance genes into sunflower breeding lines for future hybrid development.