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Title: Quantification of Sclerotinia homoeocarpa overwintering in planta and detection in commercial seed

item RIOUX, RENEE - University Of Wisconsin
item SCHULTZ, JEANETTE - University Of Wisconsin
item GARCIA, MICHELLE - University Of Wisconsin
item WILLIS, KYLE - University Of Wisconsin
item Casler, Michael
item BONOS, STACY - Rutgers University
item SMITH, DAMON - University Of Wisconsin
item KERNS, JAMES - University Of Wisconsin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 10/21/2014
Citation: Rioux, R., Willis, D., Bonos, S., Smith, D., Casler, M.D., Kerns, J. 2014. Quantification of Sclerotinia homoeocarpa overwintering in planta and detection in commercial seed. PLoS One. 10.1371/journal.pone.0110897.

Interpretive Summary: Dollar spot is the most economically important disease of turf grasses in the USA, causing significant damage to many species of turf grasses. The disease is caused by the fungus Sclerotinia homoeocarpa, and it has been assumed for many years that the disease overwinters in soil and dead leaf tissue and that it can be spread by commercial seed. This research verified both of these assumptions for creeping bentgrass, the most common turf grass on golf courses in the USA. The fungus was isolated from both symptomatic and asymptomatic leaf tissue of creeping bentgrass over a 3-year period. The fungus was also isolated from six different seed lots, representing several different cultivars of creeping bentgrass. The research revealed that S. homoeocarpa can overwinter in leaf tissue and can be introduced into new turf sods via seed, providing valuable information to develop effective control mechanisms for golf course superintendents and other turf managers.

Technical Abstract: Dollar spot is the most economically important disease of amenity turf grasses in the United States, yet little is known about the source of primary inoculum for this disease. With the exception of a few isolates from the United Kingdom, Sclerotinia homoeocarpa, the causal agent of dollar spot, does not produce spores. Consequently, it is assumed that overwintering of this organism in soil, thatch, and plant debris provides primary inoculum for dollar spot epidemics. Overwintering of S. homoeocarpa in roots and shoots of symptomatic and asymptomatic creeping bentgrass turf grass was quantified over the course of a three-year field experiment. Roots did not consistently harbor S. homoeocarpa, whereas S. homoeocarpa was isolated from 30% of symptomatic shoots and 10% of asymptomatic shoots in the spring of two out of three years. The presence of stroma-like pathogen material on leaf blades was associated with an increase in S. homoeocarpa isolation and colony diameter at 48 hours post-infection. Commercial seed has also been hypothesized as a potential source of initial inoculum for S. homoeocarpa. In this research, two or more commercial seed lots of six creeping bentgrass cultivars were tested for contamination with S. homoeocarpa using culture-based and molecular detection methods. A viable, pathogenic isolate of S. homoeocarpa was isolated from one commercial seed lot and contamination of this lot was confirmed with nested PCR using S. homoeocarpa specific primers. Nested PCR detected the presence of S. homoeocarpa contamination in five additional seed lots. Seed source, but not cultivar or resistance to dollar spot, influenced contamination by S. homoeocarpa. Overall, this research reveals potential sources of initial inoculum for dollar spot epidemics and may lead to novel options for managing pathogen introduction.