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First Report of Gliocephalotrichum bulbilium Causing Fruit Rot of Posthavest Mangosteen in China

Mangosteen (Garcinia mangostana L., Guttiferae) is a tropical fruit renowned for its pleasant taste, rich nutrition, and medicinal value. Little research about mangosteen diseases during storage and transport has been reported. In June of 2012, fruit rots on mangosteens imported from Thailand were observed in Guangzhou, China. In infected fruits, pericarps showed an increased firmness, were discolored to deep pink, and the edible aril became brown and rotten. In order to search for the etiological agent of this rot symptom, infected mangosteens were analyzed. Diseased mangosteen tissues were surface-sterilized with 70% alcohol, then with 0.1% HgCl₂, dipped in sterilized water three times, and placed onto potato dextrose agar (PDA) at 26°C. The fungi isolated from tissues of the pericarp and aril were similar in morphology and grew rapidly, covering the plate surface (9 mm diameter) after 2 to 3 days of incubation at 26°C. The morphological characters of 10 single-spore isolates were observed. These isolates showed light yellow to light brown fertile colonies on PDA. On corn meal agar (CMA), conidiophores were erect, arising from wide hyphae; they were composed of a basal stipe ending in a penicillate conidiogenous apparatus with directly subtending sterile stipe extensions ranging from 74.5 to 195.0 μm long. Conidia were unicellular, smooth, oblong to elliptical, 6.3 to 8.5 × 2.5 to 3.0 μm, and accumulated in a mucilaginous mass. Chlamydospores were multicellular, dark brown, regular in shape and thick-walled, and 40.0 to 52.5 μm in diameter. On the basis of these morphological characters, these isolates were identified as Gliocephalotrichum bulbilium (2). To confirm the identity of this fungus, genomic DNA of two isolates was extracted, and fragments of ITS region and β-tubulin gene were amplified by PCR, sequenced, and compared with sequences of Gliocephalotrichum species available in NCBI GenBank. Both DNA regions (GenBank Accession Nos. KF716166 and KF716168) had sequence similarities of 99% and 97%, respectively, to other G. bulbilium sequences at GenBank. Pathogenicity tests were conducted on three detached fruits for two isolates. Fruits were inoculated using 5-mm mycelial disks with conidia taken from 3-day-old cultures of G. bulbilium isolate Gb1 and Gb10 grown on PDA. Controls were inoculated with PDA disks only. All treated fruits were kept individually in a humid chamber at 26°C. Tests were repeated twice. Three days after inoculation, white mycelial growth for Gb was observed at inoculation sites. Eight days after inoculation, mycelium of Gb nearly covered the fruit, causing fruit rot, and the pericarp became hard and light in color. The control fruit did not rot. G. bulbilium was re-isolated from diseased plant tissue, thus fulfilling Koch's postulates. G. bulbilium has been reported causing postharvest fruit rot of rambutan (Nephelium lappaceum) and guava (Psidium guajava) in some locations (3,4). Moreover, the fungus caused cranberry fruit rot in the United States (1). To our knowledge, this is the first report of G. bulbilium causing postharvest fruit rot of mangosteen in China. It is uncertain whether the fungus infected mangosteen in Thailand and was carried to China due to commercial relationship.

References: (1) C. Constantelos et al. Plant Dis. 95:618, 2011. (2) C. Decock et al. Mycologia 98:488, 2006. (3) L. M. Serrato-Diaz et al. Plant Dis. 96:1225, 2012. (4) A. Sivapalan et al. Australas. Plant Pathol. 27:274, 1998.