Potencial do óleo essencial de cravo da índia sobre fungos fitopatogênicos em sementes de milho.

Abstract

The maize (Zea mays L.) is an important cereal due to its extensive use as human and animal staple food. Brazil is one of the largest producers and exporters of maize in the world. However, these seeds are susceptible to several phytopathogens, which cause damage during the production stages. The use of chemical pesticides is the main method used in the management of pathogens. However, indiscriminate use causes serious environmental, social and economic impacts, making necessary the development of alternative methods to reconcile safe food production, environmental preservation, and economic viability. This study evaluates the inhibitory potential of the clove essential oil (Syzygium aromaticum) on phytopathogenic fungi in vitro and on maize seeds. For this, laboratory experiments were carried out under completely randomized designs. In the in vitro test, the essential oil was incorporated into the PDA (Potato-Dextrose-Agar) culture medium and poured into Petri dishes. The treatments comprised different concentrations of the oil (0.0125, 0.025, 0.05, 0.1, and 0.2%), a negative control (0.0%), and a positive control consisting of the addition the Tiram fungicide. Plates were inoculated with the fungi Fusarium verticillioides, Macrophomina phaseolina, and Macrophomina pseudophaseolina and incubated for seven days at 27±2°C. The estimated variables were: percentage of mycelial growth inhibition (PGI) and mycelial growth rate index (MGRI). In the in vivo test, maize seeds (AG 1051 hybrid) were treated by immersion in solutions of autoclaved distilled water 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. After that, the seeds were inoculated by deposition on fungi colonies, which were cultivated in Petri dishes in BDA culture medium. The seeds remained in contact with the fungal colonies for 32 hours. Finally, the seeds were submitted to sanity test by the filter paper method with freezing. The evaluations were performed by examining the seeds under a stereoscopic microscope and the fungi identified through the morphological characteristics of their structures. Under in vitro conditions, clove essential oil inhibited the mycelial growth of F. verticillioides, M. phaseolina and M. pseudophaseolina. Total inhibition of mycelial growth (PGI = 100%) occurred at the concentration of 0.05% for the fungus F. verticillioides and 0.1% for M. phaseolina and M. pseudophaseolina, under in vitro conditions. The clove essential oil at 0.2% concentration significantly reduced the incidence of colonies of fungi M. phaseolina and M. pseudophaseolina in hybrid corn seeds AG 1051.