Identification and Toxicological Characterization of Alternaria japonica Strains.

Fungi of the genus Alternaria are producers of biologically active compounds. Alternaria japonica is pathogenic to small radish and certain other crucifers, but has not been studied in sufficient detail. Discrepant data on its toxic metabolites are available in the literature, possibly because a limited set of nutritive substrates was used in culturing or species identification of the strains was incorrect. The objectives of this study were to accurately identify the Russian A. japonica strains and to assess the A. japonica toxigenic potential. Four Russian A. japonica strains were identified using a multifaceted approach, which included analyses of morphological characters (the diameter and morphology of colonies grown on the diagnostic media potato carrot agar (PCA) and yeast extract-glucose (YES) agar for one week), the conidial size, and the presence of chlamydospores), the nucleotide sequences of DNA markers (ITS and EF1α regions), and chemotaxonomic data (mycotoxin production). Biomass and extractive substance yields of A. japonica cultures were found to significantly depend on the composition of the liquid medium. Minor differences between the A. japonica strains were detected via metabolite profiling by HPLC/MS-UV. Extracts of A. japonica cultures exerted phytotoxic activity toward small radish leaves and cytotoxicity toward Paramecium caudatum to a level comparable with that of A. tenuissima extracts. Brassicicolin A, dihydrobrassicicolin A, and phomenins A and B, which are known for several species of the genus Alternaria, were identified in A. japonica extracts. Mycotoxins (alternariol, its methyl ether, tentoxin, tenuazonic acid, and altenuene), which are characteristic of the cosmopolitan species A. tenuissima, were not detected in cultures of the A. japonica strains. Extract toxicity and the yield of extractive substances were studied in the A. japonica strains, and strain MFP244011 proved promising as a producer of known and, presumably, new toxins upon culture on the M1D synthetic medium or semisynthetic liquid media (e.g., the Sabouraud medium).

[The effect of chitosan- and vanillin-based immune modulators on the formation of plant resistance to dark-brown blotch].

The effect of chitosan- and vanillin-based immune modulators on the development of the phytopathogen Cochliobolus sativus (S. Ito & Kurib.) Drechsler ex Dastur, which induces dark-brown blotch (helminthosporiosis) in wheat, has been studied. It was shown that treatment with these substances led to a decreased injured area in leaves and an increase in the biotrophic period of pathogen development. It was found that vanillin-modified chitosan effectively provided wheat resistance to hemibiotrophic pathogen C. sativus. Changes in leaf peroxidase activity correlated with the manifestation of disease symptoms.

[Biological activity of fungi from the phyllosphere of weeds and wild herbaceous plants].

Antimicrobial, phytotoxic, and insecticidal activity of 30 fungal isolates obtained from leaves of weeds and wild herbaceous plants was assessed. Antibacterial, antifungal, phytotoxic, and insecticidal activity was found in over 50, 40, 47, and 40% of the isolates, respectively. These findings may be important for toxicological assessment of potential mycoherbicides, as well as provide a basis for investigation of the patterns of development of phyllosphere communities affected by fungal metabolites.