Abstract A serious disease of green, actively expanding
stems of young Eucalyptus grandis, E. dunnii, E. globulus
and E. globulus subsp. maidenii has been observed in
plantations in Uruguay and Argentina during the course of
the past 10 years. The symptoms of the disease are unlike
those previously observed on any species of Eucalyptus. In
this study, we describe the symptoms of this new disease
and determine its cause. A diagnostic feature of the disease
is a red discolouration of the young host tissue and
blistering of the young bark leading to rapid shoot death.
A bacterium was consistently isolated from the stem blisters
on to nutrient agar, purified and a selection of six strains
were subjected to standard phenotypic tests and 16S rRNA-,
gyrB- and rpoB-gene sequencing. The ability of these strains
to induce a hypersensitive reaction (HR) was tested on
tobacco and a pathogenicity tests were undertaken on a E.
grandis clone. The bacterium was found to be identical to
Erwinia psidii. Strains inoculated into tobacco produced a
HR within 36 h and discolouration of internal shoot tissue
was observed in the inoculated E. grandis clone. E. psidii is
known to cause die-back of guava (Psidium guajava) which
is closely related to Eucalyptus, also belonging to the
Myrtaceae. Results of this study suggest that E. psidii has
undergone a host shift to become an important pathogen of
Eucalyptusspp. that are widely planted in South America to
sustain important paper and pulp industries.