ISOLATION OF NEW PROBIOTIC MICROORGANISMS FROM SOIL AND SCREENING FOR THEIR ANTIMICROBIAL ACTIVITY

Abstract

Soil represents an extraordinary rich source of microorganisms responsible for its most important functions in terrestrial ecosystems. An important property certain of these microorganisms confer to soil is the suppressiveness, the property of soils to inhibit the development of pathogenic agents. Recent research focused on soil beneficial microbial strains reported the favourable effect of probiotic consortia of fungi, actinomycetes and other various bacteria, when applied, on increasing soil suppressiveness against soil-borne plant pathogens, plant resistance and growth improvement. The present paper presents the results of research with the aim to isolate new strains of soil microorganisms and to screen them for the capacity to inhibit or limit the development of fungal soil-borne pathogens from genera Fusarium and Phytophtora, previously isolated from soils under anthropic influence. Four fungal strains and one actinomycete have been isolated in pure culture by plating on PDA culture medium soil dilutions from two suppressive soils from Tulcea region, nearby Enisala and Visterna. The strains taxonomically identified as belonging to species Trichoderma viride (strains D4, CD2 and CF2), Verticillium tenerum (strain V1) and actinomycetal strain CG4A have been screened for their antifungal activity by dual culture method. All Trichoderma viride strains presented growth inhibition percent over 50% for Fusarium and Phytophtora pathogens. The other strains were less active in pathogen inhibition. The paper presents micrographs obtained by optical microscopy to reveal the aspects of antagonism zone between the strains and the mechanisms of biochemical interactions or the hiperparasitism evidenced during the research.