Occurrence of Botrytis cinerea on Pelargonium spp. in Argentina

Pelargonium spp. are perennial ornamental plants used as potted plants or bedding plants in gardens. During the spring and summer of 2003, symptoms of an unknown disease appeared on florists' geranium (Pelargonium inquinans (L.) L'Herit) and ivy geranium (P. peltatum (L.) L'Herit.) adult plants growing in gardens in the suburbs of Buenos Aires. Flowers showed small, water-soaked spots that expanded and eventually blighted the petals. Brown, circular to irregular, water-soaked spots developed in leaves and advanced into the peduncules. A fungus was isolated from diseased leaf tissue on potato dextrose agar after surface disinfestations in 2% NaOCl for 2 min. Pure cultures formed a whitish, dense mycelial mat and turned gray after 72 h. Conidia were ellipsoid, hyaline, nonseptate, and were formed on botryose heads with an average size of 8.6 × 10.2 μm. Black, round, and irregular sclerotia developed on 7-day-old cultures with an average size of 1.1 × 1.7 mm. Morphological characteristics agree with those described for B. cinerea Pers.:Fr (1). Pathogenicity tests were conducted. Five 3-month-old plants of each host were spray inoculated with a conidial suspension (1 × 10⁶ conidia/ml). Three controls of each host were sprayed with sterile distilled water. Plants were covered with plastic bags for 48 h and incubated at 20 ± 2°C with natural light for 15 days. Lesions similar to those observed in natural infection developed after 4 days. B. cinerea was reisolated from lesions, thus completing Koch's postulates. Controls remained symptomless. To our knowledge, this is the first report of B. cinerea causing a disease on Pelargonium. spp. in Argentina. Reference: (1) M. V. Ellis and J. M. Waller. No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI. Kew, Surrey, UK, 1974.