Evaluation and comparison of the antifungal effect of essential oil of four medicinal plants and molecular identification antagonistic bacteria against fungi decay cause of orange post-harvest by Penicillium digitatum

Citrus green mold, Penicillium digitatum is one of the most important postharvest diseases. Continuous application of chemical pesticides has serious long term effects on human health and environmental pollution that may result in emergence of resistance in pathogenic strains. In this study, antifungal activity of different concentrations (100, 200, 300, 400ppm) of four medicine plants essences including Thymus vulgaris, Cuminum cyminum,Allium sativum and Aloe vera collected from Ghorogh area of Golestan provience was evaluated. Essences were prepared by the steam distillation water using Clevenger apparatus. The main constituents' essences having the most antagonistic activity were analyzed by GC / MS. Antagonistic activity of bacteria isolated from orange epithelium including Bacillus, Pseudomonas sp., and Streptomyces sp. against Penicillium digitatum was also investigated in a completely randomized factorial model. The maximum percent inhibition (99.95%) was observed by the thyme plant essence at 400 ppm concentration. Regression analysis of the effects of essences showed that by increasing the essences concentration, its inhibitory effect on fungi increased. Based on the results, thyme essence with having the important constituents of essences (carvacrol - 45.5%), (alpha-terpineol - 22.9%) and (endo - borneol 14.3%) had the highest inhibitory effect (22.3 mmol) against penicillium. Among 23 bacterial isolates, one of them, H7, had the highest inhibitory effect on penicillium. Using PCR amplification and DNA sequencing of 16S rRNA gene, it was identified as Bacillus cereus. Thus, thyme essence and Bacillus cereus (H7) are an appropriate substitutions to chemical control of orange postharvest diseases caused by Penicillium digitatum.