RESUMO
Three ornamental species, Osteospermum sp. (L.), Felicia amelloides (L.) Voss, and Ranunculus asiaticus L., cultivated in greenhouses on the outskirts of Buenos Aires, showed sudden wilt and death during October 2002. These species are new ornamentals in Argentina. The diseased plants were cultivated in plastic containers filled with commercial potting mix. Soft rot was observed at the base of the plants. Stem lesions became covered with whitish mycelium that produced large, black sclerotia (5 to 7 mm in diameter) characteristic of Sclerotinia sclerotiorum (Lib.) de Bary (1). The fungus was consistently recovered from infected stem pieces that were disinfested for 1 min in 0.2% NaOCl and plated on potato dextrose agar (PDA), pH 7. Pathogenicity of the three isolates obtained from infected plants was confirmed by inoculating 10 3-month-old healthy plants of each species in 14-cm-diameter plastic pots. Each isolate was inoculated on the host from which it had been isolated. Inoculum consisted of three mycelial plugs from 7-day-old PDA cultures that were placed on the substrate at the base of the plants. Control plants were treated with sterile agar plugs. Inoculated and noninoculated plants were covered with transparent plastic bags for 2 days and incubated in a growth chamber at 20 to 24°C with a 12-h photoperiod. All inoculated plants developed symptoms of leaf yellowing and wilt. Soft and watery tissues were observed at the base of the plants, soon followed by the appearance of white mycelium. Disease symptoms were similar to those observed on the original infected plants and appeared 6, 5, and 3 days after inoculation on Osteospermum sp., F. amelloides, and R. asiaticus, respectively. All inoculated plants died within 3 weeks, and control plants remained healthy. S. sclerotiorum was reisolated from inoculated plants of each species, fulfilling Koch's postulates. To our knowledge, this is the first report of the occurrence of Sclerotinia stem rot on these three plant species in Argentina. Reference: (1) J. E. M. Mordue and P. Holliday. No. 513 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK. 1976.
RESUMO
During the spring of 2003, flower spots were observed on French hydrangea (Hydrangea macrophylla (Thunb.) DC) in CETEFFHO-INTA-JICA experimental greenhouses in Castelar, Argentina. Brown, irregular spots randomly distributed on petals were detected on an old, whiteflowering variety of unknown origin, cultivated by growers. Small pieces of diseased tissue were surface disinfested with 2% NaOCl, plated on 2% potato dextrose agar (PDA) with pH 7, and incubated at 22 to 24°C. Dense, whitish mycelium developed within 48 h and turned gray after 72 h. Conidia were ellipsoid, hyaline, nonseptate, and formed in botryose heads. Spores from 10-day-old colonies that were developed on PDA in test tubes were removed with 4 ml of sterile water per tube. Prior to inoculation, inflorescences were detached and placed in water-filled glass vases. To test pathogenicity, eight healthy inflorescences were sprayed with a 5-ml suspension (2 × 104 conidia per ml of sterile distilled water). Another eight healthy inflorescences were sprayed with sterile distilled water. The inflorescences were maintained at 21°C and covered with polyethylene bags that were removed after 3 days. Brown, circular-to-irregular spots appeared on petals 5 days after inoculation, became coalescent, and covered 50 to 60% of each inflorescence in 8 days. Gray mold consisting of black conidiophores and gray-in-mass conidia was observed 3 days after the development of the symptoms. Controls remained symptomless. The same pathogen was recovered from inoculated flowers and was identified as Botrytis cinerea Pers.:Fr. (1). To our knowledge, this is the first report of this fungus on Hydrangea macrophylla in Argentina. Reference: (1) M. V. Ellis and J. M. Waller. Sclerotinia fuckeliana (condial state: Botrytis cinerea).No. 431 in: Descriptions of Pathogenic Fungi and Bacteria, CMI, Kew, Surrey, UK, 1974.
