Bidens sulphurea (synonym Cosmos sulphureus) (Asteraceae), commonly known as yellow cosmos, is a native herbaceous species from Mexico that is widely used as an ornamental. It has been introduced in Brazil and has escaped from gardens, becoming a minor weed in ruderal, crop and pasture areas (2). In June 2010, groups of B. sulphurea individuals were found in a garden at the locality of Piúna, municipality of Viçosa (state of Minas Gerais, Brazil), that were severely attacked by gray mold. The disease led to flower rot with dieback of infected peduncles and stems. Plant tissues became brown to grayish brown and were covered by extensive fungal sporulation; in addition, seeds were colonized and destroyed by the fungus. A hyphomycete was regularly found associated with the diseased flowers, which was readily recognized as having a morphology typical of Botrytis cinerea: conidiophores solitary, cylindrical, terminally branched, 15 to 20 μm wide, grayish to olivaceous gray, and smooth; conidiogenous cells polyblastic, subcylindrical to ampulliform, and 120 to 230 × (13-) 14 to 16 (-19) μm; conidia ellipsoid to obovoid, 8 to 12 × 6.5 to 8 (-9) μm, with a discrete hilum at the base, 1 to 2 μm, aseptate, and hyaline. The fungus was isolated in pure culture and inoculation of one isolate on healthy B. suphurea individuals was carried out with a 2.14 × 106 conidia/ml suspension, which was sprayed to runoff onto three plants bearing four to six inflorescences. All plants were left in a moist chamber for 48 h and later transferred to a bench in a greenhouse at 21 ± 3°C. Gray mold symptoms appeared after 10 days that led to rapid and complete necrosis of flowers and peduncles. Infection first appeared on the flowers but progressed downward, leading to top dieback and finally plant death (not seen in the field). Only Botrytis cinerea was obtained in isolations from diseased flowers, demonstrating the pathogenicity of the fungus. A representative sample was deposited in the UFV herbarium (VIC 31602). The only other record of Botrytis cinerea causing gray mold of B. sulphurea is from China (1,3). To our knowledge, this is the first record of Botrytis cinerea causing gray mold on B. sulphurea in Brazil.
References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Botany and Mycology Laboratory, ARS, UDSA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/, 2011. (2) H. Lorenzi and H. M. Souza. Plantas Ornamentais no Brasil. Plantarum, Nova Odessa, Brazil. 1995. (3) Z. Zhang. Flora Fungorum Sinicorum. Vol. 26. Botrytis, Ramularia. Science Press, Beijing, China. 2006.