Pseudomonas protegens controlled brown rot (Monilinia fructicola) on peach fruit in postharvest by suppressing fungal development and inducing plant defense-related genes

Brown rot, caused by Monilinia fructicola (Wint.) Honey is one of the world's most economically important stone fruit diseases, incurring significant losses during pre-harvest and post-harvest phases. This study demonstrated the inhibitory effect of an endophyte bacterium Pseudomonas protegens (strain QNF1), isolated from Chinese leek (Allium tuberosum) roots. The in vitro experiment revealed that P. protegens significantly suppressed M. fructicola mycelial growth by 67.11 % and 95.53 % in the potato dextrose agar (PDA) and potato dextrose broth (PDB) media compared to the control. P. protegens cell-free supernatants (CFS) also restrained M. fructicola mycelial growth by 97.95 %. In addition, the in vivo experiment displayed P. protegens reduced brown rot of peach fruit inoculated with M. fructicola plug and dipped into M. fructicola fermentation broth by 81.57 % and 85.58 %, respectively. Moreover, P. protegens improved the peach fruit quality to a certain extent. In the early stage, P. protegens significantly induced defense-related genes, including superoxide dismutase (SOD), catalase (CAT), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), chitinase (CHI), and beta-1,3-glucanases (GLU). Through gas chromatography-mass spectrometry and liquid chromatography-MS analysis, 21 and 19 principal metabolites were identified in P. protegens, respectively. Among them, pyroglutamic acid, lysine, valine, tryptophan, tyrosine, and methionine were discovered by both analysis methods. The study revealed that P. protegens reduced the brown rot of peach fruit by suppressing fungal development and inducing plant defense systems. The main findings of the study proved that P. protegens represents a promising alternative for controlling the brown rot of peach fruit and other stone fruits during storage.