First Report of Blueberry Botrytis Blight in Buenos Aires, Entre Ríos, and Córdoba, Argentina

Since 2003, a new field disease has been observed on several cultivars of highbush blueberry (Vaccinium corymbosum L.) in Buenos Aires (Baradero, Colonia Urquiza, Lima, Mercedes, and San Pedro), Entre Ríos (Concordia, Gualeguaychú, and Larroque), and Córdoba (Capilla del Monte and La Cumbre). Infected flowers turned brown to tan with a water-soaked appearance and shriveled up. Blighted flowers typically did not produce fruits; even an entire cluster of berries could be aborted. A chlorotic area, that later became necrotic and turned light brown, developed when leaves were in contact with blighted flowers. A watery rot developed on fruit occasionally before harvest but more generally after harvest. Infected tender green twigs also became blighted, with leaf tissue becoming brown to black. Older twigs and stems were also blighted. Abundant, gray mycelium with conidial masses developed on all affected tissues under moist conditions. Sections of infected leaves, twigs, stems, flowers, and fruits were surfaced sterilized with 0.2% NaOCl, plated on 2% potato dextrose agar (pH 7), and incubated at 22°C. Pure cultures formed a whitish dense mycelial mat and turned gray after 72 h. Conidia were ellipsoid, hyaline, nonseptate, and formed on botryose heads. They ranged from 5.8 to 9 × 8.1 to 13.7 μm (average 8.6 × 10.2 μm). Black, round, and irregular microsclerotia developed on 7-day-old cultures with an average size of 1.1 × 1.7 mm. Morphological characteristics agree with those described for Botrytis cinerea Pers.:Fr (1). Pathogenicity was tested on 10 12-month-old potted blueberry plants cv. O'Neal by spraying a suspension of 1 × 10⁶ conidia per ml of sterile distilled water. Ten plants used as controls were sprayed with sterile distilled water. Each plant was covered with a transparent polyethylene bag for 48 h and incubated at 20 ± 2°C in humid chambers for 15 days. Lesions similar to those observed in the fields developed after 4 days and asexual fructifications developed after 5 days. The same pathogen was reisolated from the lesions, thus completing Koch's postulates. Water-treated plants remained symptomless. To our knowledge, this is the first report of a disease caused by B. cinerea on blueberry in Buenos Aires, Córdoba, and Entre Ríos provinces of Argentina. References: (1) M. V. Ellis and J. M. Waller. Sclerotinia fuckeliana (conidial state: Botrytis cinerea) No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1974.