Efficacy of biofingicides based on Bacillus against apple scab (Venturia inaequalis) and their influence on rhizosphere fungal communities

Fungal phytopathogens are a serious threat to the food security of countries. Diseases caused by them can lead to crop losses and violations in the national food security. The most common and affective control method is chemical fungicides but they can have a negative impact on crop quality, human health, as well as on the abundance and diversity of beneficial soil microorganisms. Environmentally friendly methods such as biological agents (BCAs) based on microorganisms has a proven efficacy against phytopathogens, stimulate the growth and development of plants, they are selective to target pathogens, do not form resistance, and do not have a negative effect on the beneficial soil microbiota, so they can be an ecological alternative. This research was concentrated on studying of BCAs based on Bacillus sp. against apple scab Venturia inaequalis and to assess its effect on the communities of fungi in the rhizosphere of apple trees compared with chemical plant protection products. The following plant protection systems were considered: Bacillus velezensis 336g, Fitosporin-M Zh based on Bacillus subtilis strain 26D; chemical treatment by ZATO (trifloxystrobin) and SCORE 250 EC (difenoconazole). Biofungicides on leaves and fruits demonstrated efficacy against V. inaequalis up to 80%. In the all rhizosphere samples with BCAs treatment presence of pathogens was detected, but it was on the stable level. Treatment with chemical fungicides leaded to a sharp decreasing of the fungal diversity in rhizosphere and increasing of fungal pathogens quantity, primarily Fusarium, Rhizoctonia and Verticillium when total number of fungi remained stable. So, development of phytopathogens was caused by the liberation of those ecological niches that were previously occupied by saprotrophic fungi and plant symbionts. As a result, prolonged use of chemical fungicides on apple trees may further lead to the development of root rot and other plant diseases caused by soil phytopathogens. Using of BCAs reduced the incidence of plants, but at the same time did not affect the diversity of the soil fungal communities.