Authors
Elizabeth Ngadze, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, South Africa, and Department of Crop Science, University of Zimbabwe, P.O. Box MP167, Mount Pleasant Harare, Zimbabwe;
David Icishahayo, Department of Crop Science, University of Zimbabwe, P.O. Box MP167, Mount Pleasant Harare, Zimbabwe; Teresa A. Coutinho, Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria, 0002, South Africa; and
Jacquie E. van der Waals, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, South Africa
Abstract
Pectobacterium atrosepticum, P. carotovorum subsp. brasiliensis, and Dickeya spp. cause soft rot of potato (Solanum tuberosum) worldwide. Plants respond to bacterial invasion by activating defense responses associated with accumulation of several enzymes and inhibitors, which prevent pathogen infection. This study focused on the role of polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), chlorogenic acid, and total soluble phenols in imparting resistance to soft rot pathogens. Seven and 11 varieties grown by farmers in South Africa and Zimbabwe, respectively, were used in the study. The results showed significantly higher (P < 0.001) enzyme activity of PPO and PAL as well as higher concentrations of chlorogenic acid and total soluble phenols in Vanderplank, Pentland Dell, M69/11, Romano, M59/20, and MondialZw. PAL activity increased significantly with time in all varieties, and the highest activity was recorded 8 h after cutting. The resistance of the varieties was correlated with high PPO and PAL enzyme activity as well as increased concentrations of chlorogenic acid and total soluble phenols. PPO, POD, and PAL activities increased significantly in wounded and inoculated tubers. These findings show that PAL, PPO, POD, chlorogenic acid, and total soluble phenols play a role in imparting resistance to potato soft rot infection.
