Temperature Requirements for the Colony Growth and Conidial Germination of Selected Isolates of Entomopathogenic Fungi of the Cordyceps and Paecilomyces Genera

The aim of the study was to determine the effect of temperature on the colony growth and conidia germination of selected species of entomopathogenic fungi in the genus Cordyceps (C. farinosa, C. fumosorosea and C. coleopterorum) and one isolate of Paecilomyces suffultus. In the first part of the experiment, selected isolates were grown on Sabouraud (SDA) medium at six temperatures: 5, 10, 15, 20, 25 and 30 °C. Colony growth was observed every 3 days until day 18, by measuring the colony diameter. In the second part of the experiment, slides with an SDA medium and spores were placed in incubators with the above temperature and observations on conidia germination were carried out after 24 and 48 h. The results revealed that the thermal optimum for colony growth of the fungal isolates was within the temperature range of 15 °C and 25 °C. The optimum temperature for the growth of P. suffultus colonies was 15 °C, with 20 °C for C. farinosa and C. coleopterorum. The highest thermal requirements were demonstrated by the C. fumosorosea, which developed best at 25 °C. Cordyceps farinosa and C. fumosorosea developed in a wider temperature range, from 5 °C to 30 °C. In contrast, growth of C. coleopterorum and P. suffultus colonies was observed only at temperatures between 10 °C and 25 °C. After 24 h, spore germination of the fungal species was most intense at 25 °C. After both 24 and 48 h, the temperature of 5 °C stopped the spore germination of all fungal species, and in the case of C. farinosa and C. fumosorosea no germination was also found at 30 °C. This study on the effect of temperature on the growth and spore germination of the species C. coleopterorum and P. suffultus is the first research of its type. The fungal isolates tested in this work in terms of thermal requirements have shown high pathogenicity in relation to selected plant pests in previous studies, which indicates their potential usefulness in IPM programs.