Expression of chloroplastic psbA gene in susceptible and tolerant pear cultivars in ‎response to invasion of fire blight agent and inhibitors of electron chains of the ‎chloroplasts and mitochondria

Fire blight, the most important disease of pear tree causes necrosis by an oxidative stress in tissues. Therefore, identification of resistant cultivars and mechanisms of resistance to the oxidative stress of disease, that are mainly related to the chloroplasts, are important in breeding programs of this tree.  In order to study the role of chloroplasts in this interaction, expression of chloroplastic gene psbA that are under control of oxidation/reduction (redox), was evaluated in susceptible (Williams) and resistant (Harrow Sweet) cultivars during 48 h post inoculation by Erwinia amylovora in in vitro condition. In addition, expression of this gene was studied at presence of glutaraldehyde and rotenone as the inhibitors of the electron transport chain of chloroplast and mitochondria, respectively. The results showed higher necrosis progress rate in the in vitroshootlets of susceptible cultivar. Expression of psbA gene at presence of inhibitors in both presence and absence of E. amylovora was higher in cultivars Harrow Sweet. According to the results, the higher resistance level of cultivars Harrow Sweet to the disease could be due to the higher rapid responses and reaction of the chloroplasts of this cultivar in comparison to the cultivar Williams.