Development of defense system and secondary metabolites of Korla fragrant pear during Alternaria alternata infection

Abstract

Blackhead disease causes serious postharvest loss of fragrant pear (Pyrus brestschneideri Rehd), with Alternaria alternata being the main pathogen. Herein, the changes in defense responses of fragrant pear to A. alternata were explored. The results showed that compared to sterile distilled water treatment, A. alternata inoculation promoted MDA and H2O2 accumulation, and increased LOX activity. Moreover, it decreased the activity of SOD, POD, PAL, LAC, CAD, and 4CL, and repressed the expression of PbPOD, PbLAC, Pb4CL, and PbCAD, and reduced the accumulation of defense-related substances (total phenols, total flavonoids, and lignin). In addition, compared with the control group, the activity of pathogenesis-related proteins (GLU, CHT) and the overall gene expression level increased significantly in pear inoculated with A. alternata. A. alternata infection also affected endogenous hormones in pear, especially the contents of salicylic acid and abscisic acid. Overall, the defense of pears after infection with A. alternata is lower than that of pears inoculated with sterile water.