Exploring the dynamics of entomopathogenic fungi: isolation, characterisation and growth variability in soil sample of an apple orchard

Entomopathogenic fungi (EPF) have demonstrated their potential as important biological control agents against pest species. This study investigated EPF occurrence and prevalence in a German organic apple orchard against <i>Cydia pomonella</i>, comparing virulence and chitinase production as efficacy factors. Thirty-two EPF strains were isolated from soil samples using the insect bait method and were identified using microscopic examination and molecular sequencing of the ITS, BLOC and elongation factor-1-α regions. Initial screening was based on mortality (≥80% mortality) against <i>Cydia pomonella</i> using a virulence test. Later, 13 selected strains were tested for chitinase activity using an agar-chitin plate assay, with 4 potential strains showing higher (≥1) chitinase activity. These four strains, JKI-BI-1496 (<i>Cordyceps fumosorosea</i>), JKI-BI-2620 (<i>Beauveria bassiana</i>), JKI-BI-2642 (<i>B. bassiana</i>) and JKI-BI-2647 (<i>Metarhizium robertsii</i>) were selected for experiments with environmental stress factors, such as temperature (5°C, 10°C, 15°C, 20°C, 25°C, 30°C, and 35°C) and simulated sunlight. In addition, various growth parameters such as spore productivity, production of dry biomass and optical density of fungi were evaluated in four different media (malt peptone, malt peptone with 1% chitin, potato dextrose and potato dextrose with 1% chitin) to observe the production potential of the different strains. JKI-BI-1496 showed higher tolerance for environmental stress factors (higher radial growth at 25°C and 20.4% germination after 3 h of sunlight simulation) compared to the other three strains. Conversely, adding 1% chitin to different media did not influence spore productivity, but influence dry biomass and optical density of all strains.