Association of Resistance Level to the Fire Blight (Erwinia amylovora) Disease with Chloroplastic and Mitochondrial Oxidative Stress in Two Pear Cultivars Harrow Sweet and Barteltt

Oxidative stress of the fire blight disease in host plant consists of chloroplastic and mitochondrial oxidative stresses that leads to the necrosis of tissues. This research was conducted to quantify and compare the role of oxidative stress of these organelles using glutaraldehyde as chloroplastic inhibitor of electron transport chain (ETC) and rotenone as mitochondrial inhibitor ETC. Due to the necrotic effect of inhibitors, in the primarily tests, different concentrations of inhibitors were examined under in vitro conditions and two concentrations of inhibitors (5 and 10 mg l-1) were optimized for co-cultivation tests of host-pathogen interaction. In co-cultivation tests, necrosis appearance was recorded at 48 and 72 hours after inoculation in susceptible cv. Bartlett and tolerant cv. Harrow Sweet, respectively. Although both concentrations of inhibitors postponed necrosis appearance and reduced necrosis progress rate, but in cv. Harrow Sweet, higher effects of glutaraldehyde were observed in 10 mg l-1. The higher effects of chloroplastic glutaraldehyde inhibitor demonstrated more effective role of the chloroplastic ETC in oxidative stress of pathogen in comparison with the role of mitochondrial ETC. Additionally, in susceptible cv. Bartlett, mitochondrial inhibitor caused similar necrosis progress rate to the chloroplastic inhibitor which demonstrated another evidence for more effective role of chloroplast organelle in resistance to the fire blight disease in cv. Harrow Sweet.