Aims: This study evaluates the inhibitory potential of the clove essential oil (Syzygium aromaticum L.) on phytopathogenic fungi in vitro and on maize seeds. Study Design: The experiments comprised completely randomized designs: Seven treatments with five replicates on in vitro test; and four treatments with five replicates each, on in vivo test. Place and Duration of Study: The work was carried out at the Center for Agrifood Science and Technology of the Federal University of Campina Grande, Pombal, Brazil, from April to May 2018. Methodology: In the in vitro test, the essential oil was incorporated into the PDA (Potato-Dextrose-Agar) culture medium. The treatments comprised five concentrations of the oil (0.0125, 0.025, 0.05, 0.1, and 0.2%), a negative control (0.0%), and a positive control (Tiram). Plates were inoculated with the tested fungi, Fusarium verticillioides, Macrophomina phaseolina, and Macrophomina pseudophaseolina, then incubated for seven days at 27±2°C. The percentage of mycelial growth inhibition (PGI) and mycelial growth rate index (MGRI) were estimated. In the in vivo test, maize seeds (AG1051 hybrid) were treated with the essential oil on concentrations equal or superior to the minimum inhibitory concentration found in the in vitro test, besides the negative and positive controls. The artificial inoculation was carried out in fungi colonies for 32 hours and the seed sanity test was performed. The percentage of seeds infected by the fungus was evaluated after seven days. Results: In vitro conditions, clove oil totally inhibited the mycelial growth of F. verticillioides, M. phaseolina and M. pseudophaseolina at concentrations of 0.05, 0.1 and 0.1%, respectively. At 0.2% concentration significantly reduced the incidence of colonies of fungi M. phaseolina and M. pseudophaseolina in hybrid corn seeds AG 1051. Conclusion: The clove essential oil had a fungitoxic effect on the phytopathogens evaluated, under in vitro and in the treatment of maize seeds.

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