Antifungal Activity of Thymol against Aspergillus awamori and Botrytis aclada Isolated from Stored Onion Bulbs

Abstract

The antifungal activity of thymol against Aspergillus awamori F23 and Botrytis aclada F15 in onions was examined through direct treatment with amended media and gaseous treatment with I-plates (plastic plates containing central partitions). The protective and curative control efficacy of thymol was examined 24 h before and after the inoculation of onion bulbs with the fungal isolates. Mycelial growth, sporulation, and spore germination of the isolates were inhibited on potato dextrose agar amended with various concentrations of thymol or acetic acid (positive control). Overall, thymol produced a stronger inhibitory effect on the mycelial growth and development of the isolates than acetic acid. Following gaseous treatment in I-plates, mycelial growth, sporulation, and spore germination of the isolates were inhibited at higher concentrations of thymol or acetic acid; however, acetic acid showed a little effect on the sporulation and spore germination of the isolates. Following the treatment of onion bulbs with 1000 mg L −1 of thymol 24 h before and after fungal inoculation, lesion diameter was greatly reduced compared with that following treatment with 0.5% ethanol (solvent control). Onion bulbs sprayed with thymol 24 h before fungal inoculation generally showed reduced lesion diameters by isolate F23 but not in isolate F15 compared with those sprayed 24 h after fungal inoculation. Collectively, thymol effectively inhibited the growth and development of A. awamori and B. aclada on amended media and in I-plates. In addition, spraying or fumigation of thymol is more desirable for effectively controlling these postharvest fungal pathogens during long-term storage conditions.

Phenolic compounds inhibit viability and infectivity of the grapevine pathogens Diplodia seriata, Eutypa lata, Fomitiporia mediterranea, and Neofusicoccum parvum

“…Thymol had greater efficacy than eugenol, and at 360.0 µg mL -1 , thymol completely inhibited germination of N. parvum and D. seriata conidia. A lower thymol concentration (100.0 µg mL -1 ) was sufficient to reduce F. oxysporum spore germination by 80% (Liu et al, 2022), and 100% inhibition was achieved by Oh et al (2022) for Botrytis aclada conidia. Their study also reported that Aspergillus awamoris conidia were resistant to thymol, and only treatment with 500 µg mL -1 completely inhibited germination.…”