Feature Story
Figure 1: Coalescing of necrotic spot causing larger dead areas on bentgrass fairway (on left side).
New Insights to the Population Biology of the
Dollar Spot Pathogen: Implications of Host Adaptation By Wakar Uddin, Ph.D. and Brian Aynardi, Ph.D.
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ymptoms of dollar spot are readily recognizable on low-cut turf, such as golf course tees, fairways, and putting greens, producing cream-colored necrotic lesions which result in necrotic spots of 2–5cm (approx. 0.5 –2 inches) in diameter. The spots reduce turf quality in both aesthetic value and playability. As the disease progresses the individual necrotic spots coalesce to cause large areas of high amenity turf to become blighted and form depressed or sunken areas that affect ball roll and green speeds. In higher cut turf such as in residential lawns and sports fields, the necrotic areas are typically much larger, extending to several inches in diameter. Nearly all turfgrass species used in golf courses, athletic fields, residential lawns, business parks, and sod-production areas are susceptible to dollar spot disease. The identity of the pathogen that causes dollar spot across the United States has been debated for decades, essentially since the disease was first described. Advancements in fungal genetics in the 1990s and early 2000s used molecular methods to determine that the pathogen causing dollar spot, Sclerotinia homoeocarpa, was not a member of the Sclerotiniaceae family, but rather the
14 Pennsylvania Turfgrass • Summer 2019
Rutstroemiaceae family. In 2018, published research using isolates collected from around the world studied various molecular markers to split what was once thought to be a single species into four species under a new genus, Clarireedia. Only two of the four species are predominately found in the United States, but also have global distribution; Clarireedia jacksonii occurring on cool season (C3) grasses and Clarireedia monteithiana occurring on warm season (C4) grasses. While looking at the taxonomic issues facing S. homoeocarpa, we also concurrently focused on the genetic diversity among isolates infecting cool and warm-season turfgrass species. Previously, research studies have shown that there is little genetic diversity in the pathogen population except for those infecting warm season grass hosts in Florida and the southern United States. After collecting isolates throughout the transition zone of the United States from 2011–2016, and also examining isolates from our pools of collections dating back to the 1970s, our research was able to clearly demonstrate that there are two genetically distinct types of the pathogen isolates causing dollar spot in North America: Type I, consisting primarily of isolates collected
