Response of Pear Cultivars to Invasion of Mutant Strains of Fire Blight Causal Agent (Erwinia amylovora) Based on H2O2 Generation

Pear (Pyrus communis), is the most important host of fire blight disease, and the response of pear cultivars to this disease is highly dependent on the host response related to Reactive Oxygen Species (ROS) generation especially Hydrogen Peroxide (H2O2). In order to have a better understanding of these reactions, quantitative level of H2O2 generation related to tissue response of pear cultivars during interaction with wild type Erwinia amylovora and mutant strains of this bacterium including HrpW–, HrpN– and DspA/E through active and inactive chloroplast was determined in present study. Comparison of results of evaluated indices including necrosis development and severity and percent of H2O2 production in periods of time after inoculation showed that HrpN and DspA/E effector proteins had the highest and HrpW effector protein had the lowest portion in pathogenicity and H2O2 production in host and HrpN had a key role during interaction with host chloroplast. Quantitative evaluation of the bacterial effector proteins on H2O2 generation indicates that HrpN and DspA/E effector proteins hahadve a complementary role in development of oxidative burst in pear cultivars and it seems that oxidative tension of host is caused by HrpN and due to complementary role of DspA/E it reaches to a destructive level for host tissue. Based on severity index of H2O2 Production, just development of this ROS in host is not enough for causing necrosis and increasing of its severity upper than index 3 is essential for necrosis and sensitivity.