First report of Erwinia pyrifoliae on strawberries in the Netherlands
The NPPO of the Netherlands recently informed the EPPO Secretariat of the first finding of an Erwinia species in strawberry (Fragaria ananassa) which was assigned to the E. pyrifoliae taxon. E. pyrifoliae is closely related to Erwinia amylovora (EPPO A2 List) and was initially described in 1999 in Korea on Pyrus pyrifolia (Asian or nashi pear) causing symptoms resembling those of fireblight (EPPO RS 99/134). In Japan, Erwinia isolates from P. ussuriensis or P. communis were found to be closely related to E. pyrifoliae but it is not entirely clear whether they were distinct species or not from E. pyrifoliae.
In the Netherlands, symptomatic strawberry plants collected from two different locations (glasshouse commercial crops) were received in June and October 2013 for diagnosis. The identity of the bacterium was confirmed on 23 December 2013 by the National Reference Centre (biochemical and molecular tests of pure cultures followed by pathogenicity tests on F. ananassa cv. ‘Elsanta’). Affected strawberry plants showed intense blackening of immature fruits, fruit calyx and attached stems. In many cases, fruits were also heavily distorted. No symptoms were observed on the leaves. The discolouration was obvious inside young fruits which presented an intense darkening/blackening of the fruit tissue at the edges, and the fruit tissue was extremely shiny in the middle. Release of bacterial slime was additionally observed on the surface of the young fruits and their attached stems (ooze formation). Symptomatic fruit were unmarketable. At the two different locations, symptoms were generally observed across the whole greenhouses and disease incidence was high (with approximately 50% of the plants bearing at least 1 symptomatic fruit). Pictures of symptoms can be viewed on the Dutch NPPO website:
It is noted that according to the time when infection starts during the strawberry growing season, economic losses can greatly vary from low (when infection occurs at the last stages of the cultivation for fruit production) to very high (when infection occurs at the initial stages of the cultivation for fruit production). The origin of the introduction of E. pyrifoliae in strawberry crops in the Netherlands is unknown. In 2014, a specific surveillance programme of strawberry fruit growers will be carried out to determine the distribution of E. pyrifoliae in the Netherlands. Depending on the outcome of this surveillance programme, further phytosanitary measures will be considered. Since affected crops have already been removed, no further phytosanitary measures have been taken at the affected fruit companies.
The pest status of Erwinia pyrifoliae in the Netherlands is officially declared as: Present, only in some areas, only in protected cultivation.
NPPO of the Netherlands (2014-01).
Kim WS, Gardan L, Rhim SL, Geider K (1999) Erwinia pyrifoliae sp. nov., a novel pathogen that affects Asian pear trees (Pyrus pyrifolia Nakai). International Journal of Systematic Bacteriology 49, 899-906.