Effect of Zataria multiflora essential oil on Alternaria alternata in vitro and in an assay on tomato fruits

The present study aimed to evaluate the effects of Zataria multiflora essential oil at different concentrations (0, 100, 200, 300 and 500 ppm) on the growth rate and morphogenesis of Alternaria alternata in in vitro and in vivo conditions. The antifungal activity of the oil was tested by the poisoned food technique (PF) and volatile activity assay (VA). The mycelial growth of the test fungus was completely inhibited at oil concentrations of 500 and 200 ppm in PF and VA assessments, respectively. Determination of conidial germination in the presence of the oil was also carried out and it was found that the oil caused 100% inhibition of conidial germination at the level of 300 ppm. Light Microscopy (LM) showed morphogenic changes in the test fungus with 300 ppm of the oil. These changes included a significant decrease and loss of conidiation, severely collapsed and squashed hyphae, a decreased hyphal diameter and granulation of cytoplasm. The treatment with the oil also resulted in highly lobate and bulbous anomalous structures at the hyphal tips. GC-MS evaluations of the essential oil revealed that the latter consisted of 14 compounds of which carvacrol was the major component. In vivo Z. multiflora oil at 500 ppm effectively reduced the percentage of decayed tomatoes. Findings of the current study suggest that essential oils could be used as an alternative for chemicals for control of postharvest phytopathogenic fungi on fruits or vegetables.