MATERIAL AND METHODS Sample collection Actinomycetes were isolated from soil (Haplic Fluvisol) located near Nitra (Slovakia-latitude 48° 31' 35.97'' N, longitude 18° 11' 46.82'' E), one compost, one vermicompost and soil amended with compost or vermicompost. Vermicompost and compost were applied to the soil at a total dose of 20 Mg.ha −1. The applied compost was prepared by mixing straw (11% by dry weightdw), hay (3% by dw), silage (32% by dw), sheep manure (9% by dw), cow manure (34% by dw) and soil from the subsoil (11% by dw). Vermicompost was prepared by mixing the compost (41% by dw), cow manure (20% by dw), peat and forest litter (21% by dw), soil (10% by dw), a compound of grass, straw and hay (6% by dw) and the fill vermin (2% by dw). The fill vermin (older vermicompost) containing earthworms and cocoons of earthworms (70 earthworms dm −3) was added to the compost. The basic chemical and microbial characteristics of soil samples and both composts (Table 1) were determined according to the defined values: oxidizable carbon (Cox) by the Tiurin method, total nitrogen (Nt) by the Kjeldahl distillation method, pH (H2O) and microbial biomass carbon (Cmic), which was determined by the fumigation-extraction method of Vance et al. (1987). Plant diseases caused by pathogenic fungi are a severe problem for agriculture, and some organic fertilizers have shown a suppressive capacity due to the antagonistic action of microbial communities inhabiting those substrates. The purpose of this work was to isolate and identify actinomycetes from soil, compost and vermicompost able to antagonize phytopathogens. In total, out of 352 actinomycetes successfully recovered on Pochon medium and of which were selected representative 22 mycelium forming isolates, which were subjected to morphological and genotypic characterization. Genetic characterization based on 16S rDNA fragment sequencing revealed that, all the actinomycete isolates belong to the genus Streptomyces. The antifungal activity of isolates was tested against eight phytopathogenic fungi, and they were most activated against Rhizoctonia solani, Alternaria tenuissima, Aspergillus niger and Penicillium expansum. Isolates 51VK13 (Streptomyces sampsonii) and 12VK13 (Streptomyces flavovariabilis) isolated from soil amended with vermicompost showed the greatest antagonistic activity. Their bioactive potential was also confirmed by presence of genes for nonribosomal peptide synthetase (NRPS) and polyketide synthase types I and II (PKS-I and PKS-II). It can, therefore, be concluded that soil amended with organic fertilizers such as compost, and in particular vermicompost, provides a lower incidence of phytopathogens, especially fungi. Isolated actinomycetes have also shown high potential for the production of bioactive compounds useful in the control of plant diseases. ARTICLE INFO
