Sclerotinia Homoeocarpa Infection Process and Host Preference On Various Model Plants.

Dollar spot of turfgrass, caused by the fungus currently classified as Sclerotinia homoeocarpa, occurs on many turfgrass species worldwide and is among the most important diseases with respect to pesticide expenditures. Understanding of the S. homoeocarpa infection process at both the physical and molecular level will aid in targeting weaknesses in the disease cycle yet is limited.  In this study, various plants with well-characterized genomes (Arabidopsis thaliana, Brachypodium distachyon, wheat, barley, and rice), as well as the natural host creeping bentgrass, were utilized to study the S. homoeocarpa infection process and determine host preference. Leaves of 4-week old plants were inoculated with agar plugs of 7 day-old potato dextrose agar cultures of four S. homoeocarpa isolates to monitor disease severity and progression of infection. Results on all plants were similar and showed an initial 72-hour biotrophic phase prior to the onset of host tissue necrosis.  These findings were corroborated by microscopic analysis of inoculated tissues, which indicated that the pathogen actively penetrates host cells as early as 6-hours-post inoculation. Although symptoms were produced on all species, severity was greatest on B. distachyon and barley. Lesions were phenotypically distinct on A. thaliana versus monocot species. To further examine host preference, S. homoeocarpa growth was assessed on solid and liquid media containing plant extract from all hosts. The production of oxalic acid—a toxin and possible S. homoeocarpa virulence factor—was also quantified in liquid plant amended media. Overall, this research indicates that S. homoeocarpa is a hemibiotrophic pathogen with minimal host preference and that various species for which extensive genetic resources are available could be utilized to better understand the molecular and physical processes of Sclerotinia homoeocarpa-host interactions.