Chlorophyll Fluorescence Response in Susceptible and Tolerant Pear Cultivars to Fire Blight in Active and Inactive Chloroplast Conditions

Fire blight disease in interaction with host trees causes considerable damages via oxidative burst and finally necrosis on the tissues. In this research, to investigate the role of chloroplast electron transfer chain (ETC) in this interaction, the chlorophyll fluorescence response of susceptible and tolerant in vitro pear cultivars were studied in both active and inactive chloroplast conditions. For comparison of active and inactive ETC of chloroplasts, the experiments were conducted in the sucrose presence (inactive ETC) and absence (active ETC) in the growth media. The results showed faster disease progression in susceptible cultivar, as well as in sucrose presence condition. Also, the minimum (Fo) and maximum (Fm) chlorophyll fluorescence indices were reduced in sucrose presence compared to the sucrose absence condition; Therefore, the negative role of sucrose presence in the activity of chloroplasts was confirmed. Comparing the effects of pathogen attack on Fo and Fm indices in sucrose presence and absence condition showed minimum effects of pathogen attack on Fo index in the sucrose presence condition, while this index demonstrated high variation in susceptible cultivar in sucrose absence condition.