INTRASPECIFIC VARIABILITY OF PAECILOMYCES-FUMOSOROSEUS - EFFECT OF TEMPERATURE ON VEGETATIVE GROWTH

A prerequisite to efficacious performance of Paecilomyces fumosoroseus is normal germination and growth under the environmental conditions w here the fungus will be employed. We measured the effects of temperatu re on the growth rates of 37 isolates of P. fumosoroseus originating f rom various insect hosts (principally Bemisia tabaci and B. argentifol ii and some species of Lepidoptera) from the southern United States, E urope, Pakistan, Nepal, and India. The fungus was grown on artificial media at 11 different temperatures ranging from 8 to 40 degrees C. Rad ial growth rates of surface colonies fit a linear model where the slop e corresponds to the growth rate. Optimal growth rates were observed a t 20 to 30 degrees C and ranged from 0 to 5.2 mm/day. Higher temperatu res (30-40 degrees C) were more limiting than the lower ones (8-11 deg rees C). The results showed an intraspecific variability partially rel ated to the microclimate of the fungal biotopes. Most isolates origina ting from Europe (temperate climate) exhibited a temperature range for growth from 8 to 30 degrees C, with optimal growth rates at 20, 20-25 , or 25 degrees C. The temperature range for the isolates from the sou thern United States (both humid and dry subtropical climates) and from west Asia (humid tropical climate) was broader (8-35 degrees C), with optimal growth at 25, 25-28, or 28 degrees C. Indian isolates (monsoo n climate) presented the best tolerance to high temperatures (32 and 3 5 degrees C). For optimal performance in the held, the thermal require ments of isolates should be matched to microhabitats of the target ins ect. (C) 1997 Academic Press.