Insights into the biology of sphaerobolus stellatus as a causal agent of thatch collapse in golf turfs

Symptoms consistent with thatch collapse have been observed on golf courses in New Zealand and the United States. Symptoms include circular patches ranging from 8 to 46 cm in diameter, which result in a depression in golf turf stands of creeping bentgrass (Agrostis stolonifera), annual bluegrass (Poa annua), and browntop bentgrass (Agrostis capillaris). Commonly associated with the thatch degradation was Sphaerobolus stellatus, an agaricomycete not previously reported within turfgrass stands. The primary objectives of this study were to confirm S. stellatus as a causal agent of thatch collapse; to morphologically compare isolates; and to determine cardinal temperatures for isolate growth and glebae production. Isolates were obtained from symptomatic turf from five golf courses in the United States and two golf courses in New Zealand. Colonies were creamy white, and mycelia were either appressed, stringy, or aerial. Mycelia growth increased with increasing temperature from 5 to 25°C, and more glebae were produced at 10, 15, and 20°C than at 25°C. Amplification of the ribosomal internal transcribed spacer region (ITS) with primer set ITS4/ITS5 resulted in 695 to 724 bp sequences from all isolates that had 98 to 99% similarity to known isolates of S. stellatus. Thatch degrading ability of S. stellatus was determined using the loss on ignition method and by direct measurements of thatch depth. When compared with the noninfested control, plugs infested with S. stellatus exhibited a 20 and 25% decrease of organic matter and thatch depth, respectively. Koch’s postulates were fulfilled, confirming that S. stellatus is a causal agent for organic matter degradation resulting in thatch collapse on golf turfgrass.