Carvacrol and eugenol effectively inhibit Rhizopus stolonifer and control postharvest soft rot decay in peaches

This study aimed to investigate the antifungal mechanism of carvacrol and eugenol to inhibit Rhizopus stolonifer and the control of postharvest soft rot decay in peaches.

To investigate the antifungal mechanism, the effects of carvacrol and eugenol on the mycelium growth, leakages of cytoplasmic contents, mycelium morphology, cell membrane and membrane composition of R. stolonifer were studied. Carvacrol and eugenol both exhibited dose-dependent antifungal activity against R. stolonifer, carvacrol at a concentration of 2 μl per plant and eugenol at a concentration of 4 μl per plant inhibited fungal growth completely. The two essential oils (EOs) increased cell membrane penetrability and caused the leakage of cytoplasm, nucleic acid and protein content. The observation using scanning electron microscopy and fluorescent microscopy showed modification of the hyphal morphology and breakage of the cell plasma membrane. Decreased ergosterol contents confirmed that the two EOs could destroy the membrane of R. stolonifer. For the in vivo test, the inhibition of soft rot disease and the induction of defence-related enzymes were investigated. Carvacrol and eugenol significantly reduced the incidence and severity of soft rot decay in inoculated peaches. The best treatments for controlling soft rot decay were obtained at 0·5 μl l^-1 for carvacrol and 1 μl l^-1 for eugenol. The activities of defence-related enzymes in peaches were also enhanced by fumigation with two EOs.

This study showed that carvacrol and eugenol could effectively inhibit the growth of R. stolonifer in vitro and successfully control the incidence of soft rot decay in honey peaches.

The above findings may be the main antifungal mechanism of carvacrol and eugenol on R. stolonifer. Furthermore, carvacrol and eugenol are helpful for their commercial application on the preservation of fresh fruit.