Comparison of the biocontrol efficacy of culture filtrate from Streptomyces philanthi RL-1-178 and acetic acid against Penicillium digitatum, in vitro and in vivo

Abstract

The antifungal compounds in a culture filtrate of Streptomyces philanthi RL-1-178 (culture filtrate RL-1-178) have been found to include acetic acid as their major component. The aim of this study was to compare the biocontrol efficacy of culture filtrate RL-1-178 with its major component at various concentrations, in inhibiting the growth of green mold disease from Penicillium digitatum, in vitro and in orange fruits. S. philanthi RL-1-178 was able to produce both antifungal metabolites and volatile compounds which inhibited the mycelial growth of P. digitatum. The effective dose of culture filtrate RL-1-178 was 2.5 mL/10 mL on PDA. Both culture filtrate RL-1-178 and commercial acetic acid at 1.5 mM completely suppressed the mycelial growth of P. digitatum and inhibited spore germination but did not kill the spores. Orange fruits treated with culture filtrate RL-1-178 showed less disease symptoms, disease incidence (12%) and a smaller lesion diameter (1.8 mm) than those treated with 1.5 mM acetic acid (25% and 5.6 mm, respectively). Moreover, a combination of both the culture filtrate and acetic acid (1.5 mM) was able to completely suppress the disease. The results revealed that culture filtrate RL-1-178 alone or acetic acid alone, as well as their combination were successful in controlling green mold disease.