Resistance and Activity of Phytopathogenic and Potential Antagonistic Soil Filamentous Fungi under the Action of Heavy Metals

Abstract

The increase in the proportion of phytopathogenic micromycetes in soils contaminated with heavy metals (HMs) make it relevant to study the mechanisms of their resistance. It is important for choosing effective phytopathogen control methods. The issues of interaction between metal-resistant phytopathogens and nonpathogenic species against the background of pollution remain no less relevant and need to be studied. In laboratory experiments with pure cultures of four fungal species (phytopathogenic strains Alternaria alternata and Fusarium oxysporum and nonpathogenic strains Trichoderma harzianum and Clonostachys rosea), the resistance to Cu, Zn, and Pb cations, separately added to a nutrient medium with different contents of available carbon (sucrose), was studied. Colony growth, sporulation activity, and biomass accumulation were measured. The effective concentrations, resulting in the 50% inhibition of growth parameters (EC₅₀), were calculated. The fungi under study showed different resistances to HMs. T. harzianum and C. rosea are more resistant to Zn and Pb at any available carbon content. The pairs A. alternata–C. rosea and T. harzianum–C. rosea were the most resistant to Cu on media with lower and higher carbon contents, respectively. At the same time, Zn and Pb turn out to be less toxic than Cu for all fungi. The antagonistic activity, assessed by the dual culture method on media supplemented with HM cations, depends both on the growth characteristics and on the resistance to HMs that is revealed. The activity of fast-growing T. harzianum as a territorial antagonist is stimulated by the addition of Zn and Pb. The slow-growing C. rosea shows competitiveness due to its high resistance to HMs. It is concluded that it is necessary to take into account species resistance to HMs in order to predict the development of relationships between pathogenic and nonpathogenic species in fungal communities against the background of soil pollution.