Inhibitory effect and underlying mechanism of cinnamon and clove essential oils on Botryosphaeria dothidea and Colletotrichum gloeosporioides causing rots in postharvest bagging-free apple fruits

Abstract

Bagging-free apple is more vulnerable to postharvest disease, which severely limits the cultivation pattern transformation of the apple industry in China. This study aimed to ascertain the dominant pathogens in postharvest bagging-free apples, to evaluate the efficacy of essential oil (EO) on inhibition of fungal growth, and to further clarify the molecular mechanism of this action. By morphological characteristics and rDNA sequence analyses, <i>Botryosphaeria dothidea</i> (<i>B. dothidea</i>) and <i>Colletotrichum gloeosporioides</i> (<i>C. gloeosporioides</i>) were identified as the main pathogens isolated from decayed bagging-free apples. Cinnamon and clove EO exhibited high inhibitory activities against mycelial growth both in vapor and contact phases under <i>in vitro</i> conditions. EO vapor at a concentration of 60 μL L^-1 significantly reduced the incidence and lesion diameter of inoculated decay <i>in vivo</i>. Observations using a scanning electron microscope (SEM) and transmission electron microscope (TEM) revealed that EO changed the mycelial morphology and cellular ultrastructure and destroyed the integrity and structure of cell membranes and major organelles. Using RNA sequencing and bioinformatics, it was demonstrated that clove EO treatment impaired the cell membrane integrity and biological function <i>via</i> downregulating the genes involved in the membrane component and transmembrane transport. Simultaneously, a stronger binding affinity of <i>trans</i>-cinnamaldehyde and eugenol with CYP51 was assessed by <i>in silico</i> analysis, attenuating the activity of this ergosterol synthesis enzyme. Moreover, pronounced alternations in the oxidation/reduction reaction and critical materials metabolism of clove EO-treated <i>C. gloeosporioides</i> were also observed from transcriptomic data. Altogether, these findings contributed novel antimicrobial cellular and molecular mechanisms of EO, suggesting its potential use as a natural and useful preservative for controlling postharvest spoilage in bagging-free apples.