The effects of biological control on fungal communities colonizing eggplant (Solanum melongena L.) organs and the substrate used for eggplant cultivation

Eggplants, cv. Black Beauty, were grown in the greenhouse of the University of Warmia and Mazury in Olsztyn. During the growing season, the plants were sprayed three times with Asahi SL, Biochikol 020 PC and Bravo 500 SC, they were watered with Polyversum, and a mycorrhizal inoculum was applied to the roots of seedlings. Unprotected plants, treated with distilled water, served as control. After fruit harvest, samples of the substrate used for eggplant cultivation, eggplant stems and roots were collected, and fungi were isolated in the laboratory. The fungal soil community was more abundant and diverse than the communities colonizing the stems and roots of eggplants. The applied biological and chemical control agents effectively reduced the abundance of fungi, including pathogenic species, in the organs of eggplants and the substrate used for eggplant cultivation. Potential pathogens (Alternaria alternata, Botrytis cinerea and Fusarium species) were isolated in high numbers from eggplant stems in the control treatment and in the Polyversum treatment (67%). The lowest number of potential pathogenic species were isolated from plants treated with the biostimulator Asahi SL, the fungicide Bravo 500 SC and the mycorrhizal inoculum. The population size of pathogenic fungi (Colletotrichum coccodes and Fusarium) isolated from eggplant roots was smaller, compared with stems, particularly in the treatments with the fungicide Bravo 500 SC and the biostimulator Biochikol 020 PC. The soil fungal community was dominated by yeast-like fungi (over 60% of all isolates). Fungi known as potential causal agents of diseases were found in low abundance, and they were not detected in substrate samples collected from under fungicide-treated eggplant plants.