Induced defense responses and control of blue mold of apple fruit by Zaatar (Zataria multiflora) extract

Blue mold, caused by Penicillium expansum, is considered one of the most serious postharvest diseases of apple fruits. This study was conducted to evaluate the efficacy of thyme methanol extract to control the postharvest blue mold of apple fruit and its possible modes of action through on induction of biochemical defense mechanisms. In this study, the effect of thyme methanol extract was tested on spore germination and colony growth in vitro and peroxidase activity and total phenolic in fruit tissue were evaluated by calorimetric assay. The results showed the inhibitory activity of thyme extract on P. expansum. The extract with 8-20 µg/ml concentrations had 17-33% and 24-36% inhibition of spore germination and colony growth diameter, respectively. Thyme extract decreased blue mold area by 23.63-61.20% and the most effective extract was at 13.88 mg/ml concentration. The relationship between time and thyme extract concentration in relation to decay area was described by the quadratic model. Fruits treated with thyme extract had significantly higher phenolic content and peroxidase activity than the control fruits. The highest content of phenolic compounds and peroxidase activity were achieved in the 6th and 9th days after inoculation. The results of the induction of resistance in this study suggest that the natural products used have the potential for use in the integrated management of blue mold.