First Report of Anthracnose on Chayote Fruits (Sechium edule) Caused by Colletotrichum brevisporum

Colletotrichum orbiculare is traditionally considered the etiological agent of anthracnose on such Cucurbitaceae as chayote, cucumber, melons, pumpkin, squash, and watermelon (Tocchetto 1946; Damm et al. 2013). Recently, an isolate of Colletotrichum with morphological characteristics distinct from C. orbiculare was collected from chayote fruits in Antonio Carlos, Santa Catarina State, Brazil (27°30′43″ S; 48°46′18″ W). Therefore, this study aimed to verify the etiology of anthracnose on chayote (Sechium edule) based on morphological and molecular data. The symptoms initially appear as soaked and cylindrical lesions on the surface of the fruit, which gradually enlarges in size, becomes elliptical, sunken and pale brown to black. A monosporic isolate was obtained on potato dextrose agar (PDA), and derived culture was deposited in the Coleção de Culturas de Fungos Fitopatogênicos da Universidade Federal de Alagoas (code COUFAL7300). Colonies on PDA were white to off-white, cottony to felted; and in reverse uniformly white to pale becoming orange toward the center with a growth rate of 6.61 mm/day and sparse sporulation. The hyaline, aseptate, cylindrical with round ends, smooth-walled, guttulate conidia were 7.5 to 10.5 µm long and 2 to 3 µm wide, differing from the morphological characteristics of C. orbiculare (10.5 to 12.5 µm long and 4 to 4.5 µm wide). For precise identification, partial sequences of the actin (ACT), calmodulin (CAL), chitin synthase (CHS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), internal transcribed spacer (ITS), and β-tubulin 2 (β-TUB) genomic regions were obtained and deposited in GenBank (Accession Nos. KT285378 to KT285383). The sequence of the ACT and other regions (CAL, CHS, GAPDH, ITS, and β-TUB) exhibited 100% and 99% of identity, respectively, with sequences from C. brevisporum strain GZAAS5.09545. Additionally, Bayesian inference analysis using concatenate sequences (ACT, CAL, CHS, GAPDH, ITS, and β-TUB) placed our isolate in a same clade with others C. brevisporum (study S17963 deposited in TreeBASE). To confirm pathogenicity, mycelial PDA discs of 5 mm were taken from a 7-day-old culture and deposited on five mature chayote fruits superficially wounded with a sterilized needle. In control fruits, only PDA discs without fungal growth were used. Fruits were kept for two days in a humid chamber at 25°C. This pathogenicity test was additionally carried out using commercial (Acclaim, Syngenta) and noncommercial fruits of Cucumis melo from the Melon Breeding Program of UFAL. After six days, soaked and pale-to-black, sunken lesions were observed on 100% of the inoculated fruits. No disease symptom was observed on the control fruits. To fulfill Koch’s postulates, the fungus C. brevisporum was successfully reisolated from inoculated chayote and melon fruits. This pathogen has been previously reported in Thailand and Korea in association with Neoregalia spp., Pandanus pygmaeus, and Lycium chinense (Noireung et al. 2012; Paul et al. 2014), and recently reported on papaya in Brazil (Vieira et al. 2013). To our knowledge, this is the first report of C. brevisporum causing anthracnose on chayote fruits worldwide. © The American Phytopathological Society.