Potencial fungitóxico do óleo essencial de Melaleuca alternifolia no controle de alternariose em sementes de feijão-caupi.

Abstract

The cowpea (Vigna unguiculata (L.) Walp.) has great importance for agriculture in northern and northeastern regions of Brazil. The physiological quality of seeds plays an essential role in crop yield, decreasing the occurrence of diseases in the field. 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. 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 oil (0.0125, 0.025, 0.05, 0.1, 0.2, 0.25, 0.50, 0.75, and 1.0%), a negative control (0%), and a positive control (Tiram). Discs of culture medium with fungal mycelia were inoculated in the center of the plates and incubated for seven days at 27 ±2ºC. Growth was measured to calculate the percentage of inhibition of mycelial growth (PIC) and mycelial growth rate index (IVCM). In the in vivo experiment, seeds were immersed in solutions with different concentrations of oil (0.0, 0.2, 0.5, 1.0, and 5.0%), a negative control (0.0%), and a positive control (Tiram). After the treatments, seeds were artificially inoculated with colonies of the fungus, and after that, we performed the seed sanity test. The percentage of seeds infected by the fungus was assessed seven days after the treatments. 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.