Temperature Effects On Appressorial Formation of Colletotrichum Cereale.

Turfgrass anthracnose, caused by the fungal pathogen Colletotrichum cereale, is a devastating disease on annual bluegrass (AB) and creeping bentgrass (CRB). On golf courses, intensified putting green management associated with the sand based construction has increased both incidence and severity of the disease worldwide, yet the biology of the pathogen remains unclear. An experiment was designed to investigate the effects of temperature on C. cereale appressorial formation on two different turfgrass hosts. Detatched three-week-old leaves of either AB or CRB were immersed in a conidial suspension of C. cereal for inoculation. Two fungal isolates from NC and NJ were used. Inoculated leaves were incubated in separate dark growth chambers set at one of the following temperatures: 12 C, 18 C, 22 C, 26 C, 30 C and 34 C. twenty-five arbitrarily selected conidia on each leaf blade were examined for appressorial production microscopically at 6, 12, 24, 48 and 72 hours after inoculation (HAI). Appressoria occurred over a wide range of temperatures but developed most rapidly between 18 C and 26 C, under which the majority of conidia could produce appressoria as early as 12 HAI. Lower temperatures (12 C) delayed the occurrence of appressoria but not inhibited it. At temperatures higher than 30 C, appressorial development was significantly suppressed. These results suggested that C. cereale may resume activity early in the year and infect AB and CRB well prior to the onset of symptoms.