Biochemical responses associated with common bean defence against Sclerotinia sclerotiorum

The aim of this study was to investigate changes in defence compounds of common bean cultivars with different levels of resistance to the fungus Sclerotinia sclerotiorum and determine the relation of the compounds to pathogen tolerance. The lines were inoculated with the pathogen and assessed for enzymatic and non-enzymatic parameters related to plant defence: peroxidases (POX), polyphenol oxidases (PPO), catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX), total soluble phenol and lignin contents. Stem tissue samples were collected from two regions of the plant for biochemical analyses. Stem tissue samples were collected from two regions of the plant for biochemical analyses. In the position one, 5 cm of the stem was collected from the region with necrosis caused by the pathogen, and in the position two, 5 cm of the stem was collected from the end of the position one at the times of 12, 24, 48, 72, 96 and 120 h after inoculation (HAI). Greater lignin and total soluble phenol contents and greater induction of POX and SOD activity in inoculated plants in the region near the inoculation (position one) indicate local activation with later signalling for activation of defence mechanisms in other regions of the plant. The genotype with a greater level of resistance was superior to the susceptible one in regard to lignin production and the activities of POX, APX and SOD defence enzymes. These results suggest that a combination of these defence responses in common bean may contribute to greater plant resistance to the pathogen and that these enzymes have potential use in selection of common bean genotypes.