First Report of Stigmina palmivora Causing Leaf Spots on Phoenix roebelenii in Brazil
Authors: Colmán A. , da Silva R. A. , Alves R. , Silva M. , Barreto R. W. 
Published: February 2014

Phoenix roebelenii (Arecaceae), known as dwarf date (tamareira-anã in Brazil), is a palm native to Southeast Asia and widely cultivated worldwide because of its ornamental value and ease of adaptation to a broad range of climates and soil types (4). In June 2012, some individuals were observed in a private garden in the municipality of Viçosa (state of Minas Gerais, Brazil) bearing numerous necrotic lesions on its leaves. Representative samples were taken, dried in a plant press, and brought to the laboratory for examination. A fungus was regularly associated with the leaf spots. Fungal structures were mounted in lactophenol and slides were examined under a microscope (Olympus BX 51). Spores were taken from sporulating colonies with a sterile fine needle and plated on PDA for isolation. A pure culture was deposited in the culture collection of the Universidade Federal de Viçosa (accession COAD1338). A dried herbarium sample was deposited in the local herbarium (VIC39741). The fungus had the following morphology: conidiophores grouped on sporodochia, cylindrical, 12 to 29 × 5 to 6 μm, dark brown; conidiogenous cells, terminal, proliferating percurrently (annellidic), 8 to 20 × 5 to 6 μm, pale to dark brown; conidia obclavate to subcylindrical, straight, 58 to 147 × 5 to 6 μm, 6 to 16 septate, hila thickened and darkened with a thin-walled projecting papilla, dark brown, and verrucose. The morphology of the Brazilian collections agrees well with the description of Stigmina palmivora (2), a species known to cause leaf spots on P. roebelenii in the United States (Florida) and Japan (3). Pathogenicity was demonstrated through inoculation of leaves of healthy plants by placing 6 mm diameter cuture disks of COAD1338 on the leaf surface followed by incubation in a moist chamber for 48 h and then transferred to a greenhouse bench at 21 ± 3°C. Typical leaf spots were observed 15 days after inoculation. DNA was extracted from the isolate growing in pure culture and ITS and LSU sequences were generated and deposited in GenBank under the accession numbers KF656785 and KF656786, respectively. These were compared by BLASTn with other entries in GenBank, and the closest match for each region were Mycosphaerella colombiensis strain X215 and M. irregulariamosa strain CPC 1362 (EU514231, GU2114441) with 93% of nucleotide homology (over 100% query coverage) for ITS and 98% of nucleotide homology (over 100% query coverage) for LSU. There are no sequences for S. palmivora deposited in public databases for comparison, but for Stigmina platani, the type species in this genus, 86% and 96% nucleotide homology for ITS and LSU with S. palmivora were found. The genus Stigmina is regarded as being polyphyletic (1) and this is probably reflected by these low homology levels found in the BLASTn search. To our knowledge, this is the first report of Stigmina palmivora in Brazil.

References: (1) P. W. Crous et al. Stud. Mycol. 75:37, 2012. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, UK, 1971. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab. ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , 2013. (4) H. Lorenzi et al. Palmeira no Brasil: Exóticas e Nativas, 2nd ed. Editora Plantarum, Nova Odessa, Brazil, 2005.