Transcriptional and biochemical profiling of defense enzymes in Citrus sinensis during salicylic acid and cinnamon mediated suppression of green and blue mold

Green and blue mold of citrus are threatening diseases that continuously inflict economic post-harvest loss. The suppressive effect of salicylic (SA) and <i>Cinnamomum verum</i> (CV) on green and blue mold of sweet oranges was investigated in this study. Among five tested plant extracts methanolic extract of Cinnamon caused the highest colony growth inhibition of <i>P. digitatum</i> and <i>P. italicum</i> in an <i>in vitro</i> antifungal assay. The methanolic extract of Cinnamon in combination with SA showed the lowest disease incidence and severity of green and blue mold on citrus fruit without affecting the fruit quality. Transcriptional profiling of defense enzymes revealed that the polyphenol oxidase (<i>PPO</i>), phenylalanine ammonia-lyase (<i>PAL</i>), and peroxidase (<i>POD</i>) genes were upregulated in fruit treated with CV, SA, and their combination compared to the control. The treatment SA+CV caused the highest upsurge in <i>PPO</i>, <i>POD</i>, and <i>PAL</i> gene expression than the control. Furthermore, the biochemical quantification of PPO, POD and PAL also revealed a similar pattern of activity. The present findings unravel the fact that the escalation in the activity of tested defense enzymes is possibly associated with the reduced incidence of blue and green molds. In conclusion, the study unveils the promising suppressive potential of SA+CV against green and blue mold by regulating the expression of <i>PPO</i>, <i>POD</i>, and <i>PAL</i> genes. Therefore, these treatments can find a role as safer alternatives to chemicals in the management of post-harvest green and blue mold.