Effect of temperature on growth, germination, germ-tube extension and survival of Paecilomyces lilacinus strain 251

Paecilomyces lilacinus and in particular the commercial strain 251 has been intensively tested for biological control of plant parasitic nematodes. Since this species has been mentioned in a number of reports concerning infection of humans, the human health risk for Paecilomyces lilacinus strain 251 was investigated. The effects of time, temperature and growth medium on radial colony growth and germination were determined. Additionally, exposure to 36°C and its effect on germ-tube extension and on survival of conidia was evaluated. Radial growth was significantly affected by temperature, growth medium and their interaction. Optimum temperatures were between 24 and 30°C, but no growth was found at 36°C. Germination rate was significantly influenced by time, medium, temperature and their interactions. The optimum temperature range for germination was between 28 and 30°C. Formulated conidia were capable of germinating at 36°C. However, studies on germ-tube extension conducted at 36°C showed a delay in development for 28-49 h and no further germ-tube extension was found after exposure for 80-95 h. Slopes of survival curves were significantly influenced by the type of conidia tested. In general, conidia did not survive exposure to 36°C for 168 h. These experiments indicate the temperature conditions where the strain is likely to be active and provide supporting data for full environmental and health risk assessments of biocontrol fungi.