The Effect of Humic Substances on the Colony Growth and Conidial Germination of Entomopathogenic Fungi from the Genus Metarhizium

The development of sustainable agricultural production involves the use of new plant protection products, with low toxicity to non-target organisms and high biodegradability. The aim of this study was to investigate the effect of commercially available preparations containing humic substances, in comparison with pure humic acids, on the growth and germination of spores of entomopathogenic fungi (EPFs) from the genus Metarhizium in vitro. AmiAGRA, HumiAGRA, AlgoHUM (recommended field dose) and pure humic acids extracted from peat, brown coal and spent mushroom substrate were added to Sabouraud’s culture substrate. Observation of the growth of the colonies of the tested species of EPFs was carried out every 5 days until day 20, measuring their diameter (mm). In the second stage of the experiment, the culture medium with the addition of preparations and pure humic acids was applied in a thin layer to the surface of glass slides and an aqueous solution with spores was introduced. Observation was carried out after 24 and 48 h, and the results obtained were expressed as percentages in relation to the control. The conducted research showed that on the 20th day of the culture (on average), preparations containing humic substances had a stimulating effect, while pure acids limited the growth of the colonies of the tested isolates slightly. The growth of M. anisopliae fungal colonies was most strongly stimulated by AlgoHUM, and M. flavoviride by HumiAGRA. The share of germinated spores after 48 h of contact with the substrate was higher than after 24 h, and more spores germinated on substrates with the addition of preparations containing humic substances than on pure humic acids.