Potential of Lippia sidoides essential oil in controlling Agroathelia rolfsii, the causal agent of sclerotium rot

Résumé

The fungus Agroathelia rolfsii, the causal agent of sclerotium rot (southern blight), is responsible for causing wilting and rot in the collar and roots of various agricultural crops. It is a highly destructive fungal pathogen that affects approximately 500 plant species. In addition to infecting virtually all dicotyledonous crops, this fungus can also infest some monocotyledons. Given this context, the objective of this study was to analyze the inhibition of mycelial growth of the fungus A. rolfsii in the presence of essential oil of Lippia sidoides (rosemary-pepper). The experimental design was completely randomized, with five replicates. After solidification of the culture medium (20 mL per plate), the treatments consisted of the surface application of different volumes of pure essential oil (0, 5, 25, 50, and 100 µL), corresponding to concentrations of 0; 0.25; 1.25; 2.5 and 5.0 µL mL⁻¹ (0; 0.025; 0.125; 0.25 and 0.5 % v/v), uniformly distributed on the surface of the plates. Subsequently, 1 cm diameter mycelial discs of A. rolfsii were inoculated into the central part of the plates and incubated in a BOD-type chamber under controlled temperature conditions (28 ± 1 °C) and absence of light. Mycelial growth rate index (MGRI), percentage of mycelial growth inhibition (PGI), and average mycelial growth were evaluated. The data were subjected to analysis of variance, and the means were compared using Tukey's test (5%). The results demonstrated that, starting from a concentration of 1.25 µL mL⁻¹ (25 µL), there was complete inhibition of A. rolfsii growth throughout the 12 days of evaluation. The concentration of 0.25 µL mL⁻¹ (5 µL) showed an initial inhibition of 99 %, reduced to 78 % at the end of the period, possibly due to the volatilization of the active compounds. These results indicate that the essential oil of L. sidoides shows high potential in controlling A. rolfsii, representing a promising and sustainable alternative to the use of synthetic fungicides, especially in agricultural systems with low environmental impact.