Fire blight resistance and genetic trueness-to-type of four somaclonal variants from the apple cultivar Greensleeves

Four somaclonal variants regenerated from adventitious buds of the apple va riety Greensleeves were preselected on the basis of their reduced fire blig ht susceptibility. The present study aimed at assessing precisely their lev el of fire blight resistance through various inoculation techniques (on in vitro leaves and microcuttings, on greenhouse plants and in field condition s). Overall results of these tests indicated that one clone (R 46/3) was cl early less susceptible than the control. This clone was also characterized as a 'spur' variant, with a reduced growth which can explain its limited su sceptibility to fire blight. A second clone (R 20/63) was slightly less sus ceptible than the control in greenhouse and field tests, but this low level of resistance was overcome by high concentrations of inoculum. The absence of variation in chromosome number and isozyme patterns confirmed the genet ic trueness-to-type of these four somaclones.