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First Report of Bacterial Stalk and Head Rot Disease Caused by Pectobacterium atrosepticum on Sunflower in Turkey

Bacterial stalk and head rot on sunflower (Helianthus annuus) was investigated in Konya Province of Turkey in 2008. Disease incidence was estimated as 30%. Bacteria appeared as droplets and ooze and symptoms were dark and water-soaked necrotic areas on stems and heads. Twenty-four strains were isolated from lesions on stalks and heads of sunflower cv. TR3080 from a 25-ha field and identified as Pectobacterium atrosepticum (formerly Erwinia caratovora subsp. atroseptica) (2) on the basis of biochemical, physiological (3), and molecular tests (1). Bacteria were gram negative, rod shaped, fermentative, nonfluorescent on King's B medium; positive for gelatin liquefaction, CVP test, catalase, and pectolytic activity, growth on 5% NaCl, reducing substances from sucrose, acid-production from lactose and α-methyl glucoside; and negative for growth at 37°C, acid production from sorbitol and maltose, phosphatase activity, tests for egg yolk (lecithin), sensitivity to erythromycin, and pigmentation on yeast dextrose calcium carbonate agar medium. To distinguish between P. atrosepticum and P. carotovorum, particular attention was paid to the growth at 37°C, reducing substances from sucrose and the utilization of α-methyl glucoside. Mesophyll cells of tobacco plants (Nicotiana tobaccum cv. White Burley) were infiltrated with bacterial suspensions (10⁸ cells/ml) or water (control). Brown, collapsed areas of tissues (hypersensitive response) were observed at the injection sites after incubation for 48 h at 28°C and 80% relative humidity. A P. atrosepticum-specific primer set, Y45/Y46 (3), was used in PCR reactions to generate a 439-bp DNA fragment. Reference strains, Eca17 from Aegean University, Department of Plant Protection (İzmir, Turkey) and NCPPB 1277 from Selcuk University, Department of Plant Protection, Konya, Turkey, were employed in all biochemical, physiological, and molecular tests as positive controls and similar results were obtained. Koch's postulates were carried out to establish a causal relationship between the bacteria and the disease. A bacterial suspension (10⁸ CFU/ml) was injected into sunflower shoot tips and inoculated plants were incubated for 2 weeks at 28°C and 80% relative humidity. All bacterial strains obtained from the stalks and heads produced the rot symptoms and ooze following inoculation to the susceptible sunflower cv. TR 3080. No symptoms were observed on controls that were inoculated with sterile water. The bacteria were isolated from the lesions on stalks and heads and their identities confirmed by the biochemical, physiological, and molecular tests. All tests were performed three times on three plants per strain. To our knowledge, this is the first report of P. atrosepticum on sunflower in Turkey. Further research is needed to determine how far the disease is spread in Turkey since other provinces also grow sunflowers.

References: (1) L. Gardan et al. Int. J. Syst. Evol. Microbiol. 53:381, 2003. (2) L. Hauben et al. Syst. Appl. Microbiol. 21:384, 1998. (3) A. Darrasse et al. Appl. Environ. Microbiol. 60:298, 1994.