A new pathogen, Xanthomonas arboricola pv. fragariae, causing bacterial leaf blight of strawberry: Addition to the EPPO Alert List
So far, Xanthomonas fragariae (EPPO A2 quarantine pest) was the only known economically important bacterial disease of cultivated strawberry. During autumns/winters 1993 to 1995, unusual symptoms attributed to X. fragariae were observed on many cultivars in both experimental and production fields near Cesena, Emilia-Romagna, Italy. On the lower leaf surface, small, reddish-brown lesions, which were neither water-soaked nor translucent were observed at the initial stage of the disease. On the upper leaf surface, such lesions appeared as reddish spots. Bacterial exudate was never observed. Lesions then enlarged and became surrounded by a chlorotic halo. In some cases, along the leaf margins, large brown V-shaped lesions surrounded by a chlorotic halo were also observed. Frequently, midribs, major veins and petioles also showed lesions which, as they enlarged, caused a blackening of plant tissues. The final stage of the disease is a complete yellowing and whitening of the leaf. No symptoms were observed on flowers, peduncles or fruits. In preliminary descriptions, the disease was called bacterial leaf blight of strawberry. A gram-negative bacterium was consistently isolated from lesions. It was characterized (biochemical tests, fatty acid analysis, protein electrophoresis, serology, PCR, pigment analysis, ice-nucleation activity, AFLP, DNA hybridisation, pathogenicity and host range) and described as a new and distinct pathovar called Xanthomonas arboricola pv. fragariae. During characterization studies, 2 bacterial isolates from France, previously attributed to X. fragariae, were finally identified as Xanthomonas arboricola pv. fragariae, which suggested that this new pathogen may also be present in France. In host range studies, artificial inoculations caused infections also on Begonia natalensis, Ficus elastica and Philodendron scandens.
Xanthomonas arboricola pv. fragariae (bacterial leaf blight - a new disease of strawberry)
Why: A new bacterial disease of strawberry (distinct from Xanthomonas fragariae) called bacterial leaf blight has recently been reported from Italy (Emilia-Romagna) in experimental and commercial fields. Although more data is needed on this new bacterium and in particular on the severity of the disease it causes, the EPPO Secretariat decided to add it on the Alert List.
Where: Italy (Emilia-Romagna), probably also present in France but to be confirmed.
On which plants: Strawberry (Fragaria ananassa). Infections could be obtained by artificial inoculations to Begonia natalensis, Ficus elastica and Philodendron scandens.
Damage: Leaf lesions (small reddish brown on lower leaf surface and reddish spots on the upper leaf surface) which never appear water-soaked or translucent. Lesions when enlarging become surrounded by a chlorotic halo. Final stage of the disease is a complete yellowing and whitening of the leaf. No symptoms are observed on flowers, peduncles or fruits. No data is yet available on crop damage or losses caused by the bacterium in areas where it is present.
Dissemination: No data for the moment.
Pathway: Plants for planting of strawberry from areas where the disease occur.
Possible risks: Strawberry is an important crop for the EPPO region. Bacterial diseases are difficult to control in practice. Although more data is needed on the geographical distribution, host range, biology, epidemiology, economic damage of the bacterium, the spread of a new bacterial disease could represent a threat to strawberry cultivation in Europe.
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EPPO RS 2002/061
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Panel review date: -
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Entry date 2002-04
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Sources
Janse, J.D.; Rossi, M.P.; Gorkink, R.F.J.; Derks, J.H.J.; Swings, J.; Janssens, D.; Scortichini, M. (2001) Bacterial leaf blight of strawberry (Fragaria (x) ananassa) caused by a pathovar of Xanthomonas arboricola, not similar to Xanthomonas fragariae Kennedy & King. Description of the causal organism as Xanthomonas arboricola pv. fragariae (p. no., comb. nov.). Plant Pathology, 50(6), 653-665.