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First Report of Papaya Fruit Anthracnose Caused by Colletotrichum brevisporum in Brazil

Papaya fruits (Carica papaya L.) (cv. Golden) showing post-harvest anthracnose symptoms were observed during surveys of papaya disease in northeastern Brazil from 2008 to 2012. Fruits affected by anthracnose showed sunken, prominent, dark brown to black lesions. Small pieces (4 to 5 mm) of necrotic tissue were surface sterilized for 1 min in 1.5% NaOCl, washed twice with sterile distilled water, and plated onto potato dextrose agar (PDA) amended with 0.5 g liter^–1 streptomycin sulfate. Macroscopic colony characters and microscopic morphology characteristics of four isolates were observed after growth on PDA (2) for 7 days at 25°C under a 12-hr light/dark cycle. Colonies varied between colorless and pale brown in reverse, with orange conidial mass. Conidia were hyaline, aseptate, cylindrical with round ends, slightly flattened, smooth-walled, guttulate, and 13.5 (10.5 to 17.1) μm × 3.8 (2.1 to 4.8) μm (l/w ratio = 3.5, n = 50), typical of Colletotrichum spp. DNA sequencing of partial sequences of actin (ACT) gene and the internal transcribed spacer (ITS1-5.8S-ITS2 rRNA) were conducted to accurately identify the species. Sequences of the papaya isolates were 99% similar to those of Colletotrichum brevisporum (GenBank Accession Nos. JN050216, JN050217, JN050238, and JN050239). A phylogenetic analysis using Bayesian inference and including published ACT and ITS data for C. brevisporum and other Colletotrichum species was carried out (1). Based on morphological and molecular data, the papaya isolates were identified as C. brevisporum. Conidia of the papaya isolates were narrower than those described for C. brevisporum (2.9 to 4.8 μm and 5 to 6 μm, respectively) (1), which may be due to differences in incubation temperature or a typical variation in conidial size in Colletotrichum species (3). Sequences of the isolates obtained in this study are deposited in GenBank (ACT Accession Nos. KC702903, KC702904, KC702905, and KC702906; ITS Accession Nos. HM163181, HM015851, HM015854, and HM015859). Cultures are deposited in the Culture Collection of Phytopathogenic Fungi of the Universidade Federal Rural de Pernambuco, Recife, Brazil (CMM 1672, CMM 1702, CMM 1822, and CMM 2005). Pathogenicity testing was conducted with all four strains of C. brevisporum on papaya fruits (cv. Golden). Fruits were wounded at the medium region by pushing the tip of four sterile pins through the surface of the skin to a depth of 3 mm. Mycelial plugs taken from the margin of actively growing colonies (PDA) of each isolate were placed in shallow wounds. PDA discs without fungal growth were used as control. Inoculated fruits were maintained in a humid chamber for 2 days at 25°C in the dark. After 6 days, anthracnose symptoms developed that were typical of diseased fruit in the field. C. brevisporum was successfully reisolated from symptomatic fruits to fulfill Koch's postulates. C. brevisporum was described from Neoregalia sp. and Pandanus pygmaeus in Thailand (1). To our knowledge, this is the first report of C. brevisporum in Brazil and the first report of this species causing papaya fruit anthracnose.

References: (1) P. Noireung et al. Cryptogamie Mycol., 33:347, 2012. (2) B. C. Sutton. The Genus Glomerella and its anamorph Colletotrichum. CAB International, Wallingford, UK, 1992. (3) B. S. Weir et al. Stud. Mycol. 73:115, 2012.