Evaluation of anti-biofilm property of Perilla frutescens essential oils against plant pathogenic fungi

More than 10,000 species of fungi are responsible for extensive damage to plant. These microorganisms grow on plants in the form of biofilms, communities of microorganisms adhering to a surface and embedded in a self-produced polymeric matrix giving origin, in most cases, to diseases. The traditional approach used for the control of biofilm consists in the use of antimicrobials. However, issues such as the risk to develop resistance, the toxicity to human health, the impact on the environment as well as the EU restrictive directives and regulations have discouraged the use of antimicrobials in the agricultural field. An alternative strategy to biocides consists in using sub-lethal doses of non-toxic natural substances involving mechanisms subtler than the simple killing activities, like those influencing the multicellular behaviour of a phytopathogen (e.g., adhesion, cell-to-cell communication, EPS production, motility). In addition, as these substances do not exert their biocidal action, they do not impose a selective pressure causing the development of resistance. In this work the efficacy of two essential oils extracted from the leaves of the Asiatic plant Perilla frutescens has been evaluated for their anti-biofilm activities at sub-lethal concentrations against the model plant pathogenic fungi Fusarium oxysporum, Fusarium dimerum and Colletotrichum musae. The obtained results showed that both essential oils (at concentrations ranging from 0,001 to 2000 ppm) i) were not a nutritional source for the fungal models; ii) did not affect the fungal grow; iii) showed a good anti-biofilm activity against F. oxysporum, F. dimerum and C. musae reducing spore adhesion up to 70%, 80% and 40 % respectively. In conclusion, P. frutescens essential oils could be proposed as a good candidate as an innovative anti-biofilm agents against plant pathogenic fungi.