Does Turfgrass Seed Serve As a Source of Initial Inoculum for Sclerotinia Homoeocarpa?.

Dollar spot, caused by Sclerotinia homoeocarpa, is a destructive pathogen of both cool and warm-season grasses worldwide.  Typically multiple applications of fungicides are required to control dollar spot during conditions conducive for development. Dollar spot management has been complicated by the development of fungicide resistance, the loss or limitation of effective broad-spectrum fungicides and a growing concern of the environmental impact of repeated fungicide usage.  In order to develop more sustainable management practices for this disease, the biology of this pathosystem must be elucidated. The source of initial inoculum is unknown for S. homoeocarpa, therefore we developed experiments to investigate the feasibility of S. homoeocarpa colonization of creeping bentgrass (CRB) seed.  Ten CRB ('Penncross') seeds were placed in a circle onto potato dextrose agar (PDA) amended with antibiotics.  A total of 1400 seeds were plated for each replication and 3 replications were conducted to date.  Fungal growth emanating from the seeds was transferred to fresh PDA and identified using morphological and molecular characteristics.  Of the seed plated, only 0.07% was contaminated with S. homoeocarpa.  A second experiment was conducted to confirm S. homoeocarpa's ability to colonize CRB seed.  Forty grams of seed were placed into 4 different beakers containing 20 mL of DI water. Seed groups were treated to achieve the following groups: non-infested, infested, disinfested/non-infested, and disinfested/infested.  Eighty seeds were plated from each group and this was repeated 4 times.  Contamination rates for non-infested, infested, disinfested/non-infested, and disinfested/infested were 0.3, 22, 8.75 and 97 % respectively. Assuming a contamination rate of 0.07% and typical golf green seeding rates, roughly 12,600 seeds could be contaminated with S. homoeocarpa. Our results suggest that turfgrass seed could be an important source for S. homoeocarpa inoculum.