Preharvest calcium chloride treatments enhance post-harvest peach fruit resistance to Monilinia fructicola-induced brown rot disease

Abstract

Monilinia fructicola-induced brown rot disease can lead to substantial post-harvest losses in peach fruit, with major economic effects. Calcium chloride (CaCl₂) treatment has been reported to mitigate brown rot in peaches, but the underlying molecular mechanisms involved remain largely unexplored. In this study, preharvest application of CaCl₂ significantly reduced the incidence of brown rot in post-harvest peach fruit. Transcriptome analysis identified 208 differentially expressed genes during the 12–48 h post-infection period in CaCl₂-pretreated peach that were predominantly associated with plant hormone signal transduction, plant-pathogen interaction, flavonoid biosynthesis, and amino sugar and nucleotide sugar metabolism. Preharvest CaCl₂ treatment raised calcium levels and Ca^2 +-sensor activity in infected fruit, boosting PpRBoh activity and transcription coincided with a reactive oxygen species burst. Moreover, CaCl₂ treatments also increased methyl jasmonate (MeJA) content via upregulating expression of PpLCAT3, PpLOX, PpAOS, PpAOC, PpOPR, and PpJMT in α-linolenic acid metabolism, thereby activating the jasmonic acid (JA) signaling pathway. Conversely, CaCl₂ treatment decreased indole-3-acetic acid (IAA) content via downregulating expression of PpTAA1, PpALDH, PpYUCCA1 in tryptophan metabolism, leading to a suppression of the IAA signaling pathway. Additionally, CaCl₂ treatment elevated the levels of pathogenesis-related proteins, flavonoids, total phenolics and anthocyanins by stimulating phenylpropanoid metabolism. Furthermore, the weighted gene co-expression network analysis identified six gene modules of co-expresses genes, with blue and green modules significantly linked to the levels of flavonoids, total phenolics, anthocyanins and the activities of CHS, F3H, DFR, ANS, and BZ1, showing that polyphenolics biosynthesis is particularly related to the JA signaling gene PpMYC2 and the JAs biosynthesis genes. Consequently, CaCl₂ sprays offer a promising alternative to chemical fungicides for mitigating peach fruit loss caused by M. fructicola infection during storage.