Effect of Zataria multiflora​ Boiss and Thymus vulgaris​ L. essential oils on black rot of ‘Washington Navel’ orange fruit

• Thymol, carvacrol and para-cymene were the most abundant constituents in both EOs.
• Alternaria citrigrowth was prevented at 300 μl l−1Zataria multiflora EO.
• Alternaria citrigrowth was prevented at 400 μl l−1Thymus vulgarisEO.
• Black rot was controlled in ‘Washington Navel’ orange using both EOs.

This research was conducted to investigate the effects of Zataria multiflora and Thymus vulgaris essential oils on Alternaria decay (black rot) development and quality traits of ‘Washington Navel’ oranges both in vitro incubated at 25 °C for 7 days and in vivo​ at 5 °C for 60 days. Based on the results obtained from GC–MS analysis, thymol, carvacrol and para-cymene were the most abundant of all constituents in EO extracts of Z. multiflora and T. vulgaris. Alternaria citri growth was completely prevented at 300 and 400 μl l−1in vitro concentrations of Z. multiflora and T. vulgaris ​EOs, respectively. Moreover, the fungal growth steadily decreased with increasing EOs concentration. Similar results were obtained from in vivo assays with 300 μl l−1Z. multiflora EO and 400 μl l−1T. vulgaris EO which showed the best effects in preventing fruit decay, without impairing fruit quality traits such as visual appearance, weight loss, firmness, peel color parameters (hue angle, chroma, and lightness), and juice chemical characteristics (endopolygalacturonase enzyme activity, antioxidant activity, total phenols, ascorbic acid and carotenoid content). The greater efficiency of Z. multiflora compared with T. vulgaris EO may be due to its higher concentration of the main constituents, especially thymol and carvacrol. Overall, Both Z. multiflora and T. vulgaris EOs could be an alternative to chemical fungicides without health risks for preserving orange fruit during cold storage.