Virulent and avirulent isolates of Pseudomonas syringae subsp. savastanoi as colonizers of olive leaves: evaluation of possible biological control of the olive knot pathogen.
The epiphytic survival of virulent and avirulent (IAA-deficient mutants) isolates of P. s. pv. savastanoi and their ability to colonize the olive phylloplane, was monitored for up to 30 d after artificial inoculation of several olive cultivars. After an initial decrease in numbers, the virulent bacteria multiplied and established a potential inoculum on olive leaf surfaces. In contrast, the numbers of avirulent bacteria rapidly diminished, so that they were eventually no longer detectable. Under the conditions used, none of the avirulent mutants (producers or non-producers of bacteriocins) were able to compete with or successfully inhibit the virulent isolate in vivo. It is suggested that this was probably due to the lack of epiphytic multiplication of the avirulent mutants. This paper was presented at the joint MPU/EPPO conference on olive diseases held in Sounion, Greece on 5-8 May 1992.