Spectrum of Biological Activity of the Alternaria Fungi Isolated from the Phyllosphere of Herbaceous Plants

Abstract

Antimicrobial, phytotoxic, and insecticidal activity of 20 isolates of 16 Alternaria species isolated from above-ground organs of weeds and wild herbaceous plants was determined. Assessment of the antibacterial activity by the agar blocks and paper disks methods revealed antibacterial activity against Bacillus subtilis and/or Pseudomonassyringae in over 70% of the isolates. Antifungal activity against Candida tropicalis was found in 30% of the isolates. The reporter system used in the work revealed no effect of the studied extracts on the ribosomes, although some of them inhibited topoisomerase. Extracts from the culture liquid of all Alternaria spp. isolates were toxic to isolated leaves of Arabidopsis thaliana and Elytrigia repens. Insecticidal activity of the extracts against vetch aphid (Megoura viciae) larvae was revealed in 40% of the isolates. Thus, fungi from the phyllosphere of weeds and wild herbaceous plants may exhibit a broad range of biological activity. This feature may probably be of practical importance for toxicological assessment of those weed pathogens that are evaluated as potential bioherbicides. Our results show that Alternaria fungi may play a significant regulatory role in formation of the communities of phyllosphere organisms and are promising producers of antimicrobial compounds with potentially new mechanisms of action.