Epidemiology of Erwinia pyrifoliae, a new pathogen on strawberry in The Netherlands

During the late spring of 2013 strawberry plants (Fragaria × ananassa Duch. 'Elsanta') were showing an intense blackening of their immature fruits, their fruit calyxes and the peduncule were found at several locations (greenhouses) in The Netherlands. Symptoms include brown petals, green young fruits turning brown, malformed fruits and bacterium slime (ooze) formation on the surface of the young fruits. Fruits did not develop or were in many cases heavily malformed. In certain cases 40% of the crop was lost. Isolations from these symptomatic immature strawberry fruits yielded Erwinia-like colonies on YPG (yeast peptone glucose) agar. The isolates differed biochemically from E. amylovora and they were closely related to biochemical profiles of the Erwinia pyrifoliae reference strain LMG 25888. The isolates were further identified as E. pyrifoliae based on the real time PCR assay. Pathogenicity of several isolates was tested and confirmed on potted strawberry plants ('Elsanta' and 'Selva'). Honeybees from pollinating colonies were tested to detect E. pyrifoliae in a flowering strawberry greenhouse cultivation. Host range, mechanisms of survival and spread of this new Erwinia species on strawberry will be discussed.