Temperature Effects on Formation of Appressoria and Sporulation of Colletotrichum Cereale on Two Turfgrass Species

Anthracnose, caused by Colletotrichum cereale, can be a devastating disease of annual bluegrass (ABG) and creeping bentgrass putting greens. Intensified putting green management has increased the frequency and severity of the disease worldwide, yet much of the biology of the pathosystem remains unclear. We investigated the effects of temperature on the formation of appressoria by C. cereale on attached and detached leaves of 3-wk-old ABG and creeping bentgrass. Leaves were inoculated with a conidial suspension of C. cereale and then incubated in the dark in growth chambers set at temperatures ranging from 12 to 34°C with high relative humidity (>95%). Leaf samples were taken over a 72-h period and examined for the percentage of conidia that germinated and produced an appressorium. Appressoria were observed at all temperature regimes but developed most rapidly between 22 and 28°C and were significantly hindered at temperatures above 30°C. Appressoria development was delayed on attached leaves compared with detached leaf pieces. Our results suggest that C. cereale can infect ABG and creeping bentgrass well before the onset of symptoms and may warrant application of preventative fungicides earlier than currently recommended.