Antifungal Activity of Non-Volatile Low-Molecular-Weight Exometabolites of Trichoderma spp. Strains Against Phytopathogenic Micromycetes

The species of the genus Trichoderma are well known as effective antagonists of a wide spectrum of micromycetes. The actual biopreparations for the control of phytopahogenic micromycetes based on separate Trichoderma strains with a high level of antagonism constantly appear on the market. The high interest of scientists in representatives of this genus is due to their wide spectrum of different mechanisms of antifungal activity that synergistically determine the high antagonistic properties of these strains. The ability to synthesize non-volatile low-molecular-weight exometabolites is rightly considered one of the main mechanisms of antifungal activity of Trichoderma spp. strains. Considering this, the evaluation of the antifungal potential of exometabolites of 48 Trichoderma spp. strains against a wide line of test cultures of phytopathogenic micromycetes (12 strains) and the selection of the most active strains among them for more in-depth studies was the main task of this work. Methods. The cultures of studied Trichoderma strains were grown on the surface of wheat grain for 21 days. For the extraction of biologically active exometabolites, chloroform was used. The antifungal activity was studied by a paper disk method. Statistical Microsoft Excel and Origin 8.0 (OriginLab) packages were used for data processing. Results. The results of the studies allowed us to divide Trichoderma spp. into five groups according to their antifungal activity. Among other studied ones are the “weakly active” Trichoderma strains that showed activity against 1–3 test cultures formed the biggest (38%) group. The second group (21%) united the “moderately active” strains with antifungal activity against 4–6 test cultures. The “highly active” strains (13%) with activity against 7–8 test cultures of phytopathogenes formed the smallest group. 15 % of studied Trichoderma strains that were active against 9 or more test cultures entered into the group of the “most active strains”. The extracts of strains 2932, 3108, and 2926, which suppressed the growth of accordingly 12, 11, and 10 studied test cultures of phytopathogenic micromycetes, were in this last group. Finally, 15% of strains formed the “non-active” group. Thus, almost half of Trichoderma strains (47%) demonstrated moderate and high levels of antifungal activity. Conclusions. The obtained results testify to a high level of antifungal activity of non-volatile low-molecular-weight exometabolites of Trichoderma spp. against phytopathogenic mictomycetes. As for the general role of non-volatile exometabolites in the manifestation of antifungal properties by Trichoderma spp strains as the trait of the whole genus, this role among other mechanisms (growth rate, synthesis of hydrolytic enzymes, mycoparasitism, etc.) is predominant according to our research. Nevertheless, some strains, as we indicated above, can be characterized by other ratios of mechanisms of antifungal activity. Hence, the representatives of the Trichoderma genus are one of the most perspective groups of micromycetes as the source of biologically active metabolites with antifungal properties.