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© 2012 Plant Management Network.
Accepted for publication 7 March 2012. Published 17 May 2012.


Leaf Spotting of Turkish Filbert in Colorado Caused by Xanthomonas arboricola pv. corylina and Pseudomonas syringae pv. syringae


Jorge Ibarra, Graduate Student, and Jacob Snelling, Research Associate, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177; Kathleen Alexander, City Forester, City of Boulder Forestry, 5200 Pearl Street, Boulder, CO 80301-2437; and Ned Tisserat, Professor, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177


Corresponding author: Ned Tisserat.  ned.tisserat@colostate.edu


Ibarra, J., Snelling, J., Alexander, K., and Tissera, N. 2012. Leaf spotting of Turkish filbert in Colorado caused by Xanthomonas arboricola pv. corylina and Pseudomonas syringae pv. syringae. Online. Plant Health Progress doi:10.1094/PHP-2012-0517-01-BR.


Turkish filbert (Corylus colurna L.) is a medium-sized tree native to southwest Asia and southeast Europe. It is well adapted to urban settings, although its use as an ornamental in the United States has been limited (1). In 2010 and 2011, Turkish filberts at a site in Boulder, CO, USA, exhibited leaf spotting, partial defoliation, and shoot dieback (Fig. 1). Small, black angular leaf spots formed along leaf margins and veins resulting in leaf crinkling. Tan to brown lesions with a translucent sheen dotted the bark on twigs whereas shepherd’s crooks formed on blighted succulent shoots. Bacterial streaming was consistently observed in necrotic tissue. Approximately 5 to 10% of the canopy in each tree was affected. Trees were well maintained and did not appear to be suffering from drought or other stresses that may have contributed to the disease. However, spring weather in both years was cooler and wetter than normal.


 
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Fig. 1. Symptoms caused by Xanthomonas arboricola pv. corylina in Turkish filbert include: (A) crown thinning resulting from defoliation and shoot blighting; (B) small, black angular spots concentrated on the leaf veins and margins; (C) tan twig lesions; and (D) shepherd’s crook formation in blighted shoots. Pseudomonas syringae pv. syringae was also isolated from leaf spots.

 

Two different bacteria were cultured on nutrient agar from leaf spots; the first isolate had smooth, yellow colonies whereas the second was translucent and exhibited irregular colony margins. Only bacteria with yellow colonies were isolated from blighted shoots. The yellow bacterium had sequence similarities of 99% to the 16S rDNA and gyrB (partial sequence only) respectively, of Xanthomonas arboricola pv. corylina (blast.ncbi.nlm.nih.gov/Blast.cgi). The translucent bacterium had sequence similarities of 99% and 98% to the 16S rDNA and to hrpL, respectively, of Pseudomonas syringae pv. syringae. Furthermore, a 752-bp fragment was amplified using primers specific to the syringomycin gene, syrB (Fig. 2). This distinguished our isolate from Pseudomonas syringae pv. coryli, which lacks syr B and is associated with leaf spotting and blighting of European filbert (C. avellana) in Italy (4).


 

Fig. 2. Amplification of the syringomycin gene, syrB, from a Pseudomonas syringae pv. syringae isolate collected from Turkish filbert in Colorado (lane 2) and an isolate from bean (lane 3). Pseudomonas syringae pv. coryli lacks syrB and has only been found in European filbert in Italy.

 

The upper and lower leaf surfaces of four, one-year-old Turkish filbert trees were brushed to runoff with bacterial suspensions (107 cfu/ml) of X. arboricola pv. corylina, P. syringae pv. syringae, or a mixture (1:1 v/v) of both species. Leaves of an additional four trees were brushed with distilled water. Trees were placed in a mist chamber for three days and then transferred to a greenhouse. After five days, a few angular, necrotic spots developed in leaves inoculated with one or both bacteria, but not in leaves treated with water (Fig. 3). No additional spotting was observed for the next month, but by seven weeks post-inoculation the number of leaf spots had increased to approximately the same severity in trees inoculated both with X. arboricola pv. corylina and with the mixture of X. arboricola pv. corylina and P. syringae pv. syringae, but not in those inoculated with P. syringae pv. syringae alone (Fig. 3). The two bacteria consistently were isolated from lesions. In the case of the mixed inoculation, both X. arboricola pv. corylina and P. syringae pv. syringae were recovered from the same lesions.



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Fig. 3. Leaf spot symptoms in Turkish filbert: five days post inoculation with (A) a mixture of Xanthomonas arboricola pv. corylina and Pseudomonas syringae pv. syringae; and seven weeks post inoculation with (B) P. syringae pv. syringae, (C) X. arboricola pv. corylina, and (D) a mixture of the two bacteria.


Xanthomonas arboricola pv. corylina is an important pathogen of European filbert in nut production areas (2,3). Turkish filbert has been listed as a host of X. arboricola pv. corylina in Europe (3), and Miller et al. (2) successfully reproduced symptoms in this species following artificial inoculations in Oregon in 1949. However, we were unable to find any published reports of natural infection of Turkish filbert in the United States. Thus, North American arborists should be aware of potential damage caused by this bacterium to this host. We did not reproduce shoot blight by artificial inoculation, but the dieback we observed in Turkish filbert is consistent with symptoms caused by X. arboricola pv. corylina in European filbert. We also documented that P. syringae pv. syringae can contribute to leaf spotting in Turkish filbert.


Literature Cited

1. Dirr, M. A. 1998. Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics, Culture, Propagation and Uses, 5th Edn. Stipes Publ., Champaign, IL.

2. Miller, P. W., Bollen, W. B., and Simmons, J. E. 1949. Filbert bacteriosis and its control. Agric. Exp. Stn. Tech. Bull. 16. Oregon State College, Corvallis, WA.

3. OEPP/EPPO. 1986. Data sheets on quarantine organisms: No. 134, Xanthomonas campestris pv. corylina (Miller et al. 1940) Dye 1978. OEPP/EPPO Bulletin 16:13-16.

4. Scortichini, M., Rossi, M. P., Loreti, S., Bosco, A., Fiori, M., Jackson, R. W., Stead, D. E., Aspin, A., Marchesi, U., Zini, M., and Janse, J. D. 2005. Pseudomonas syringae pv. coryli, the causal agent of bacterial twig dieback of Corylus avellana. Phytopathology 95:1316-1324.