Biochemical changes and defence responses during the development of peach gummosis caused by Lasiodiplodia theobromae

Abstract

Peach gummosis is a disease caused by Lasiodiplodia theobromae and a major problem in peach production. The disease is characterized by gum exudation from fungal infection sites on tree trunks, branches, and fruits. In this study, we found that high humidity and mechanical wounds promote gummosis development, whereas different light intensities and temperature do not affect gummosis after infecting detached current year shoots of the susceptible peach cultivar ‘Spring snow’ with L. theobromae in a laboratory. The chlorophyll a and b contents of the infected shoots were significantly lower than those of the uninfected control shoots, but those of H2O2 and malondialdehyde were increased in the infected tissues. Anthocyanin content and phenylalanine ammonia lyase (PAL) activity were significantly higher in the infected shoots at 1 day after inoculation, which is consistent with significant increases in the transcript levels of genes encoding enzymes involved anthocyanin biosynthesis, such as PAL, chalcone synthase, and flavanone 3-hydroxylase. The transcript levels were induced for defence-related genes, namely, chitinase, beta-1,3-glucanase, polygalacturonase-inhibiting protein, and pathogenesis-related protein 4, but down-regulated for pathogenesis-related protein 10. Cell walls were seriously degraded in response to L. theobromae infection, as observed under transmission electron microscopy. Accordingly, the transcript levels of genes that encode cell wall–degrading enzymes, such as beta-galactosidase, pectin methylesterase 1, and endo-polygalacturonase, were significantly increased in infected peach shoots.