Pectobacterium atrosepticum (Pa), P. carotovorum subsp. brasiliensis (Pcb) and
Dickeya spp. cause soft rot of potato 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 eleven 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.