Control of Alternaria alternata Using Melaleuca Essential Oil (Melaleuca alternifolia)

Aims: This study aimed to evaluate the fungitoxic potential of melaleuca essential oil on the mycelial growth of Alternaria alternata under in vitro condition and the treatment of cowpea beans.

Study Design: The experiments comprised completely randomized designs: Eleven treatments with five replicates on in vitro test; and six treatments with five replicates 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, since February 2018 to February 2019.

Methodology: In the in vitro experiment, the essential oil was incorporated into the culture medium and poured into Petri dishes. The treatments consisted of different concentrations of the essential oil (0.0125, 0.025, 0.05, 0.1, 0.2, 0.25, 0.50, 0.75, and 1.0%), a negative control (0.0%), and a positive control (Thiram). Discs of culture medium with fungal mycelia were inoculated in the center of the plates and incubated for seven days at 27±2ºC. The percentage of mycelial growth inhibition (PGI) and the index of mycelial growth speed (IMGS) was calculated to verify the difference between treatments. In the in vivo experiment, the bean seeds were treated with different concentrations of EO (0.0, 0.2, 0.5, 1.0, and 5.0%), a negative control (0.0%), and positive control (Thiram). Seeds were inoculated with colonies of the fungus for 48 hours, and after that, we performed the seed sanity test.

Results: Under in vitro conditions, all concentrations of melaleuca essential oil reduced the mycelial growth of A. alternata. The oil reached complete inhibition of fungal growth from 0.2% concentration and above. In the cowpea treatment, the essential oil had no significant control over the percentage of infected seeds.

Conclusion: The melaleuca essential oil had a fungitoxic effect on the A. alternata under in vitro conditions. However, using the adopted methodology, on the cowpea bean seed treatment, the essential oil did not reduce the incidence of A. alternata.