Evaluation of Salvia officinalis antifungal properties on the growth and morphogenesis of Alternaria alternata under in-vitro conditions

Alternaria alternata is a fungal plant pathogen causing several diseases and postharvest damages in some plants. The present study aimed to evaluate the effects of Salvia officinalis essential oil at different concentrations on the growth rate and morphogenesis of Alternaria alternata Keissl. The antifungal activity of the oil was evaluated using the poisoned food technique and volatile activity assay. The mycelial growth of the test fungus was completely inhibited at the oil levels of 500 and 300 ppm in direct contact and fumigation assessments, respectively. Assessment of conidial germination by different concentrations of oil showed that the oil exhibited 100% inhibition of conidial germination at 500 ppm. Microscopic observations using Light Microscope showed morphogenic changes in the test fungus with 300 ppm of the oil. These changes consisted of a significant decrease and loss of conidiation, severe collapsed and squashed hyphae, cytoplasm granulation and decreased hyphal diameter. The treatment with the oil also resulted in a highly lobate and bulbous anomalous structure on the hyphal tips. GC-MS and GC-FID evaluations of the Sage oil revealed that it was consisted of 28 compounds, of which camphor and ?-thujene were the major components.