First report of bacterial leaf spot disease, caused by Xanthomonas axonopodis pv. begoniae, on begonia in Turkey

In the spring of both 2003 and 2004, serious outbreaks of a suspected bacterial leaf spot disease were observed on tuberous non-stop begonia plants (Begonia x tuberhybrida cvs. Futta, Kleo, Apricot and Red) and strawberry begonia (Saxifraga sarmentosa) grown for potted production in commercial greenhouses located in Adana, Manisa, Yalova and Istanbul provinces of Turkey. The initial symptoms of the disease were small round spots and angular necrotic areas on leaf surfaces (Fig. 1). A general leaf yellowing and necrosis followed the spotting. Defoliation, open stem canker and vascular discoloration were observed on plants in advanced stages of the disease (Fig. 2).

Disease incidence was recorded in the range of 15-30% over two years. Isolations were made from leaves and stems of the affected plants on YDC agar.Bacteria consistently isolated from the diseased tissues formed yellow-coloured mucoid and convex colonies on the media. Eighteen bacterial strains were purified and used for further studies. All isolate were characterised as non-sporing, gram negative, rod-shaped, motile, aerobic, oxidase-negative, catalase-positive and amylolytic-positive (Schaad et al., 2001). All of the bacterial strains isolated in the present study were identified as Xanthomonas axonopodis pv. begoniae (Xab; Vauterin et al., 1995) based on fatty acid methyl ester analysis (Yeditepe University, Istanbul, Turkey) with similarity indices ranging from 51 to 77 % (Chase et al., 1992) and indirect-ELISA tests (Agdia BRA 23700) (Benedict et al., 1990). All of the test results were similar to those of the reference strain used in this study.

Pathogenicity was confirmed by spray inoculation of the leaves on tuberous begonia and strawberry begonia plants. Sterile distilled water and a reference strain (BPIC 2013, Xanthomonas axonopodis pv. begoniae) were used as negative and positive controls respectively. All plants were covered with polyethylene bags for 48 hour at 25°C. After inoculation, water-soak and necrotic symptoms were observed on tuberous and strawberry begonia plants within 5-7 days (Fig. 3-4). No symptoms were observed on control plants. This is the first report of Xab in commercial floriculture in Turkey and to the best of our knowledge is also the first report of infection of strawberry begonia by this pathogen anywhere.