Exploiting actinomycete biodiversity in Arctic soils to find new biocontrol agents of fungal pathogens

Fungal plant pathogens pose a significant threat to global crop production. Although synthetic fungicides are commonly used in the field to control these pathogens, their application can have detrimental effects on the environment, the broader biosphere, and human health. The sustainability of the agricultural sector is closely linked to the development of alternative approaches to chemical control. In this context, actinomycetes are particularly important due to their ability to produce a wide range of secondary metabolites with antimicrobial activity. The exploitation of this group of bacteria could lead to the discovery of new possible biocontrol agents (BCAs) or bioactive molecules. In this study, soil and rhizosphere samples were collected in different regions of Greenland. A total of 167 bacteria isolates were obtained and characterized using cultivation-dependent methods. Based on morphological traits, sixty-four strains of actinomycetes were selected for screening of their biological control activity. Their direct antagonistic activity was evaluated using a dual culture assay against six phytopathogenic fungal species (Sclerotinia sclerotiorum, Botrytis cinerea, Fusarium culmorum, Fusarium oxysporum f.sp. basilici, Alternaria alternata, and Alternaria tenuissima), belonging to three families (Sclerotiniaceae, Nectriaceae, and Pleosporaceae). Some actinomycetes caused strong fungal growth inhibition exceeding 75%, with the strongest antimicrobial activity against S. sclerotiorum, reaching up to 86%. Phylogenetic analysis based on 16S rRNA gene sequencing allowed to identify these isolates and assess the microbial diversity of Greenlandic soils and rhizosphere, revealing a predominance of the Streptomyces genus. These results support the discovery of novel BCAs or active compounds for sustainable plant pathogen management.