In vitro system for studying the interaction between Erwinia amylovora and genotypes of pear

A new in vitro system is described for studying an interaction between Erwinia amylovora and Pyrus communis (L.). The system uses single shoots placed onto the solid medium, and it enables to detect changes in pH of the medium and differential appearance of shoot necrosis. Shoots of susceptible cultivar (Williams) and tolerant cultivar (Harrow Sweet) were compared measuring the necrosis rate along the in vitro shoots and the pH variation following proton extrusion of both plant and pathogen. Shoots acidified differentially the culture medium depending on the presence of the pathogen, cultivar susceptibility and shoot inoculation methods. Differences in the tolerance level against pathogen among the cultivars were distinguishable only when the shoots were inoculated at the basal end. In susceptible cultivar, the necrosis appeared after 48 h of inoculation, while in tolerant cultivars after 72 h. This system is repeatable and more reliable than already known methods, such as in vitro leaf explants or in vivo plants; it can be used all around the year to test the gene expression and products essential to characterize the genes involved in the pathogenesis. This system showed the effects of E. amylovora on the photosystem dependent system of host cells, confirmed by the effects of pathogen attack on the variation of chlorophyll a and chlorophyll b ratios and positive effects of light on the appearance of the first disease symptoms.