Defence responses of pepper (Capsicum annuum L.) infected with incompatible and compatible strains of Phytophthora capsici

In this study, we investigated the activities of beta-1,3-glucanase and peroxidase enzymes in the leaves of pepper cultivar A3 infected with the incompatible strain PC and the compatible strain HX-9 of Phytophthora capsici. The activities of beta-1,3-glucanase and peroxidase enzymes substantially increased in the incompatible interactions compared to the compatible interactions. We also analysed the expression patterns of four defence-related genes, including CABPR1, CABGLU, CAPO1 and CaRGA1, in the leaves and roots of pepper inoculated with different strains of P. capsici. All gene expression levels were higher in the leaves than in the roots. Markedly different expression patterns were observed between incompatible and compatible host-pathogen interactions. In the incompatible interactions, the expression levels of CABPR1, CABGLU and CAPO1 genes in leaves increased by a maximum of 17.2-, 13.2- and 20.5-fold at 24, 12 and 12 h, respectively, whereas the CaRGA1 gene expression level increased to a lesser degree, 6.0-fold at 24 h. However, in the compatible interactions, the expression levels of the four defence-related genes increased by a maximum of 11.2-, 8.6-, 7.9- and 2.0-fold at 48, 24, 48 and 72 h, respectively. Compared to the leaves, the expression levels of the four defence-related genes were much lower in the roots. The highest levels of mRNA were those of the CABPR1 gene, which increased 5.1-fold at 24 h in the incompatible and 3.2-fold at 48 h in the compatible interactions. The other three genes exhibited lower expression levels in the incompatible and compatible interactions. These results further confirmed that defence-related genes might be involved in the defence response of pepper to P. capsici attack.