Blueberry blight caused by Bipolaris cynodontis in Argentina

Blueberry (Vaccinium corymbosum) production in Argentina has grown remarkably in the last eight years due to the high demand worldwide in the off-season fresh market. Since it is a new crop in Argentina, diseases are just starting to become problematic for farmers. Surveys have been conducted since 2000 to detect new pathogenic associations and to evaluate their distribution, incidence and severity in different blueberry varieties and localities.

Blueberry plants cv. Duke with dieback, and bud and branch blight, were observed in the winter of 2006 in La Plata, Buenos Aires province. Diseased pieces were washed with running water, disinfected with 2% sodium hypochlorite, then 70% alcohol, rinsed in sterile distilled water, plated on carrot agar (CA), and incubated for 12 h under near UV light until colony maturation. Under optic microscopy, conidia that were single, fusiform, straight or slightly curved, 30-50 (46.7) x 11-22 (18.4) μm, 3-7 distoseptate (mostly 5-6), pale to mid-golden brown, with bipolar germination, were observed (Fig. 1). Based on these characteristics, the fungus was identified as Bipolaris cynodontis (Marig.) Shoemaker (Sivanesan, 1987). The strain was deposited in the culture collection of the Instituto de Micología Spegazzini (La Plata, Buenos Aires, Argentina), No. 1018.

Pathogenicity tests were carried out using two-month-old blueberry plants cv. O'Neal inoculated with a suspension containing 10⁶ conidia/ml. Sterile distilled water was sprayed on controls. Plants were maintained in a humidity chamber at 20°C ± 2°C for 48 h, and incubated under 12 h light until symptoms developed. The fungus was recovered from inoculated plants that displayed similar symptoms to those observed in the field. Control plants did not show symptoms. B. cynodontis has been isolated from Cynodon, other grasses, apple, pine, Ipomoea, and Lycopersicon and is seed-borne on Agropyron, Hordeum and Triticum (Sivanesan, 1987). In Argentina, this fungus has been found on leaves of Bromus unioloides (Sisterna & Wolcan, 1989) and Cynodon dactylon (Sisterna & Dal Bello, 1991-1992) and on cereal seeds (Sisterna, 1987). This is the first report of Bipolaris cynodontis on blueberry in Argentina.