Variations in defense related enzyme activities in tomato during the infection with bacterial wilt pathogen

The present investigation was focused on the role of defense-related enzymes in imparting resistance in tomato against bacterial wilt pathogen Ralstonia solanacearum. Twenty different tomato cultivars were collected from private seed agencies and screened for resistance to bacterial wilt disease, using artificial inoculation technique under greenhouse conditions. Involvement of defense related enzymes in bacterial wilt pathogenesis was studied in resistant, susceptible and highly susceptible tomato cultivars. Eight-day-old seedlings were root dip inoculated with a bacterial suspension (1 x 10(8) cfu/ml) and harvested at different time intervals (0, 3, 6, 9, 12, 15, etc., up to 72 h) and assayed for two defense-related enzymes. Temporal accumulation of peroxidase and lipoxygenase enzymes showed maximum activity at 9 h after pathogen inoculation (hpi) in resistant cultivar, whereas in susceptible and highly susceptible cultivars it increased at 15 and 24 h for peroxidase and 18 and 27 h for lipoxygenase respectively. Furthermore, in native polyacrylamide gel electrophoresis analysis, five isoforms of peroxidase and three isoforms of LOX were observed in the resistant cultivar. Resistant cultivar showed higher enzyme activity after pathogen inoculation when compared to uninoculated control and also the susceptible cultivars. The role of these two defense-related enzymes in imparting resistance to tomato against bacterial wilt pathogen is discussed.