Intraspecific Variability ofPaecilomyces fumosoroseus:Effect of Temperature on Vegetative Growth

Abstract

A prerequisite to efficacious performance ofPaecilomyces fumosoroseusis normal germination and growth under the environmental conditions where the fungus will be employed. We measured the effects of temperature on the growth rates of 37 isolates ofP. fumosoroseusoriginating from various insect hosts (principallyBemisia tabaciandB. argentifoliiand some species of Lepidoptera) from the southern United States, Europe, Pakistan, Nepal, and India. The fungus was grown on artificial media at 11 different temperatures ranging from 8 to 40°C. Radial growth rates of surface colonies fit a linear model where the slope corresponds to the growth rate. Optimal growth rates were observed at 20 to 30°C and ranged from 0 to 5.2 mm/day. Higher temperatures (30–40°C) were more limiting than the lower ones (8–11°C). The results showed an intraspecific variability partially related to the microclimate of the fungal biotopes. Most isolates originating from Europe (temperate climate) exhibited a temperature range for growth from 8 to 30°C, with optimal growth rates at 20, 20–25, or 25°C. The temperature range for the isolates from the southern United States (both humid and dry subtropical climates) and from west Asia (humid tropical climate) was broader (8–35°C), with optimal growth at 25, 25–28, or 28°C. Indian isolates (monsoon climate) presented the best tolerance to high temperatures (32 and 35°C). For optimal performance in the field, the thermal requirements of isolates should be matched to microhabitats of the target insect.