The biocontrol efficacy and antibiotic activity of Streptomyces plicatus on the oomycete Phytophthora capsici

• Biological control efficacy of S. plicatus B4-7 on P. capsici was tested.
• Hyperparasitism of S. plicatus B4-7 against P. capsici was confirmed.
• The anti-Phytophthora compound of B4-7 was identified as borrelidin.

A Streptomyces plicatus isolate B4-7 was obtained from a citrus farm. B4-7 suppressed up to 75% mycelial growth of Phytophthora capsici, Phytophthora cinnamomi, Phytophthora palmivora and Phytophthora parasitica in the dual culture test on PSA plates. The hyperparasitism of B4-7 against P. capsici was confirmed under the scanning electron microscope. The chitin-potato sucrose broth, potato sucrose broth, rice bran broth and oatmeal broth cultural filtrates of B4-7 inhibited the mycelial growth and the zoospore germination of P. capsici in the in vitro tests. Abnormal formation of P. capsici zoospores were observed by light microscope after treating with B4-7 cultural filtrates for 24 h. When the B4-7 cultural filtrates and P. capsici zoospore were inoculated simultaneously on bell pepper leaves, 100% disease suppression was observed. In the pot test, the B4-7 oatmeal (OM) cultural broth when added 3 h post inoculation of P. capsici showed 75% crown rot disease reduction. The anti-fungal compound purified from B4-7 OM cultural broth was identified as borrelidin using spectral analysis. The results suggested that S. plicatus B4-7 could be a good biocontrol agent to be integrated in the Phytophthora blight management program.