Growth and antifungal activity of streptomycetes influenced by acidic conditions

The acidity, as an edaphic factor, affects considerably the soil inhabitants. Because of an increase in soil acidity, the direct depression of plant growth occurs, and the microscopic fungi can dominate in microbiocoenosis due to higher acidic resistance if compared to that of most bacteria. The laboratory experiments were carried out to estimate growth and antifungal activity, influenced by acidic pH, in three strains, Streptomyces hygroscopicus A-4, S. felleus A-3 и Streptomyces sp. A-24, isolated from rhizoshere of oat (Avena sativa) variety Argamak plants grown on sod-podzol acidic soil. For S. hygroscopicus А-4 and Streptomyces sp. А-24 growth the value of рН 5.5-6.5 was detected as optimum, whereas the highest growth rate of S. felleus A-3 was observed at рН > 7, i.e. under less acidic conditions. A wide pH range (pH from 4.0 to 10.0 with maximum at pH 4.5) was indicated for antifungal activity of S. hygroscopicus А-4. Streptomyces sp. А-24 and S. felleus A-3 strains depressed fungi at рН 5.0-10.0 and 7.0-10.0, respectively. Due to higher activity, the strain S. hygroscopicus A-4 was selected as a potential producer of antifungal substances for plant bioprotection. We evaluated the biological activity of this strain in phytotron using winter rye (Secale cereale L.) variety Byatka 2 and clover (Trifolium pratense L.) variety Trio seeds inoculated with S. hygroscopicus А-4 spore suspension. The strain can grow and depress Fusarium sporotrichiella, F. oxysporum, F. avenaceum, Bipolaris sorokiniana, Alternaria sp. in sterile soil under increased acidity (рН 4.0) and also in rhizosphere and rhizoplana of the plants grown at рН 4.5, resulting in their lower death because of the phytopathogen infection. At that there was no toxic effect of S. hygroscopicus А-4 to the plants.