First report of crown gall of apricot (Prunus armeniaca) caused by Agrobacterium tumefaciens in Turkey

In the winter of 2002, nearly 30% of two-year-old apricot trees (Prunus armeniaca cv. Ninfa) in two commercial orchards in Adana and Mersin, in the eastern Mediterranean region of Turkey, were observed with grown gall symptoms (Fig. 1). Tumours and galls were often found at or just below the soil surface on the roots or crown region of the apricot plants as described by Ogawa et al. (1995). A non-fluorescent, Gram-negative bacterium was isolated from diseased tissues onto King's medium B. Fifteen representative strains were characterised as aerobic, non-sporing, non-pigmented, rod-shaped, oxidase negative and catalase positive. Fatty acid analysis identified the strains as Agrobacterium tumefaciens with similarity indices ranging from 94.6 to 98.2% (Bouzar et al., 1993).

Pathogenicity of the strains was tested on carrot slices in Petri dishes and five week-old tomato plants (cv. H-2274) by needle inoculation of bacterial suspensions containing 10⁸ CFU per mL in 8.5 g/L saline. A reference strain of A. tumefaciens, GSPB 7, and saline were used as positive and negative controls respectively. Inoculated and control plants were maintained in a controlled climate room, for 20 days at 25°C and 70% RH to observe symptom development. Gall symptoms on carrot slices developed within 7-8 days (Fig. 2) and on tomato plants within 15-20 days (Fig. 3). No symptoms developed on negative control plants. The bacterium was re-isolated from inoculated tomato plants and identified as A. tumefaciens. Occurrence of crown gall disease on rose (Rosa spp.) cultivars in Turkey has been reported previously (Aysan & Sahin, 2003). However, this is the first report of the crown gall on apricot trees grown in Turkey. To the best of our knowledge, the apricot cuttings in both orchards were imported from outside of Turkey. Therefore, it is possible that the pathogen may have been introduced into Turkey with the cuttings.