Feasibility of rating fire blight susceptibility of pear cultivars (Pyrus communis) on in vitro microcuttings

Typical symptoms of fire blight (ooze production and necrosis) can easily be obtained from the inoculation of in ritro microcuttings of a host plant.The purpose of the study was to determine whether the susceptibility of pear cultivars to fire blight can be evaluated in vitro.In a work based on several Pyrus cultivars (susceptible and resistant) propagated in vitro, the effects of different external factors (method of inoculation, concentration of inoculum, growing conditions) on quantitative and qualitative expression of symptoms were analyzed.The variability of the results, already noticed in orchards, was not lessened on this plant material.Inoculations on in vitro microcuttings usually overestimated susceptibility.However, a decrease of the receptivity of susceptible cultivars was sometimes observed.Therefore tests on in vitro microcuttings do not seem to be suitable for accurate discrimination between cultivars based on their different levels of susceptibility.Nevertheless these tests may be useful for selecting out individuals with high levels of resistance from a population (i.e. after mutagenic treatment or induction of somaclonal variations).