Salicylic acid promoted apple metabolic responses against Penicillium expansum infection

Abstract Blue mold caused by Penicillium expansum ( P. expansum ) infection results in severe postharvest deterioration of apples. Salicylic acid (SA) is an effective elicitor that promotes fruit resistance. However, the metabolic mechanism of P. expansum infection of apples and the SA-mediated metabolic responses are still unknown. In this study, the metabolic changes during apple P. expansum infection and SA-mediated disease resistance were explored by performing ultra-performance liquid chromatography and quadrupole-time of flight mass spectrometry. A total of 472 different metabolites were identified between samples, and the correlated metabolic pathways were revealed by bioinformatics analysis. The upregulation of the tricarboxylic acid (TCA) cycle, galactose metabolism, and starch and sucrose metabolism reflected energy conversion for P. expansum invasion and fruit disease resistance. Changes in glyoxylate and dicarboxylate metabolism and carbapenem biosynthesis reflected the biosynthesis of virulence factors and secondary metabolites for fungal infection. Metabolic pathways related to apple natural disease resistance mainly included the upregulation of secondary metabolite biosynthesis and sphingolipid metabolism. SA promoted the TCA cycle, reactive oxygen metabolism and secondary metabolite biosynthesis of apples for disease resistance. This study improved the understanding of the pathogenic mechanism of P. expansum infection of apples and the metabolic processes for SA-mediated disease resistance.