Preliminary Study on Cell Wall-Degrading Enzymes and Host Resistance of Prunus davidiana Infected by Wilsonomyces carpophilus

The Prunus davidiana (Carrière) Franch. is an important tree species in Northwest China. However, fungal perforation caused by Wilsonomyces carpophilus can harm a variety of stone fruits, such as P. davidiana, seriously affecting the protection of germplasm resources and the cultivation of stone fruit in economic forests. In this study, the main pathogenic factors and host resistance strategies were explored by detecting the main cell wall-degrading enzymes, the activities of the resistant enzymes and substances produced by the host when W. carpophilus infects P. davidiana. In the present study, the pathogenicity of W. carpophilus (CFCC 71543) was determined on P. davidiana. The changes of six cell wall-degrading enzymes, including carboxymethyl cellulase (Cx), β-glucosidase, polymethylgalacturonase (PMG), polygalacturonase (PG), polygalacturonate trans-eliminase (PGTE) and pectin methyl trans-eliminase (PMTE), produced by different strains when they invaded the host were determined using 3,5-dinitrosalicylic acid and ultraviolet colorimetry. Additionally, the changes in phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), total phenol (TP), plant flavonoids, tannins and four other resistant substances were determined 2–16 days after inoculation. The results showed that the main cell wall-degrading enzyme of the strain (CFCC 71543) when infecting P. davidiana was PMG, with enzyme activity as high as 1548.456 U/g at 4 dpi, which was 3.988 times that of the control group. The level of five antioxidant enzymes and four resistant substances increased by varying degrees after infection by W. carpophilus. The main resistance enzyme of P. davidiana was POD, and POD activity reached 4184.889 U/g 8 days after inoculation, which was 4.074 times that of the control group. The main resistant substance was MDA, and the MDA content reached a peak of 217.63 nmol/g 8 days after inoculation, which was 2.376 times that in the control group. This is the first study to demonstrate that PMG is key in the infection of P. davidiana by W. carpophilus. The host produces five enzymes to resist infection by pathogenic bacteria, among which POD activity is the highest. Among the four resistant substances, MDA had strong resistance; the content of other resistant substances did not increase exponentially, and the resistance effect was not pronounced. These results provide a theoretical basis for an in-depth understanding of the pathogenic mechanism and are of great significance for the prevention and control of perforations.