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Gu H.,Hainan Key Laboratory for Postharvest Physiology | Gu H.,Chinese Academy of Sciences | Zhan R.-L.,Hainan Key Laboratory for Postharvest Physiology | Zhan R.-L.,Chinese Academy of Sciences | And 6 more authors.
Plant Disease | Year: 2015

Fruitlet core rot caused by Fusarium ananatum, a serious pineapple [Ananas comosus (L.) Merr.] fruit disease, has been reported in South Africa and other regions of the world (Jacobs et al. 2010). A disease that resembled fruitlet core rot was observed on pineapple cv. Comte de Paris fruits in Xuwen County, Guangdong Province, China, in March 2014. Approximately 10% of the harvested fruit were affected. Typical external symptoms included infected fruitlets that remained green or were delayed in maturity. Internal browning was observed in the center of the affected fruitlet and the rot occasionally spread to the fruit core. The brown flesh, which remained quite firm, was a type of dry rot, and was usually limited to a single infected fruitlet. The flesh between macerated and healthy tissue of 5 symptomatic fruitlets from 5 fruit was cut into small pieces (0.5 cm × 0.5 cm), surface-sterilized with 0.1% HgCl2 solution for 1 min, and cultured on potato dextrose agar (PDA) at 28°C. After 5 days of incubation, four fungal colonies were observed, and each was purified by single conidial isolation. Pathogenicity studies were conducted with pineapple plants at anthesis stage. A 15-ml spore suspension (1 × 106 spores/ml) of each fungal isolate was sprayed evenly onto the opening flowers of one inflorescence. Five inflorescences were inoculated for each isolate, while the controls sprayed sterile water. Symptoms typical of fruitlet core rot were observed within 9 to 10 weeks after inoculation on all the five inflorescences inoculated with isolate GH0305, while control plants and those inoculated with other isolates were symptomless. GH0305 was reisolated from the symptomatic plants. To identify the fungus, the isolate was cultured on PDA at 28°C and natural light cycle. Seven days after incubation, white aerial mycelia was present and was concentrated at the center of the plate and thin at the edges. Ten days after incubation, saffron pigmentation was observed on PDA. The fungus was cultured on synthetic low-nutrient agar (SNA) for micro-morphology observation (Summerell et al. 2003). After 5 days of incubation at 28°C, morphological characteristics were found to be identical to those of F. ananatum (Guarro 2013). Microconidia grew on erect conidiophores with false heads bearing monophialides. No conidia chains were observed. Microconidia were ovate to long and oval, 0 to 1 septate, and 5 to 15 × 2 to 4 µm. Macroconidia were straight or falcate, 1 to 3 septate, 15 to 40 × 3 to 6 µm, with an acute or coniform apical cell. Chlamydospores were absent. To confirm identity of the causal fungus, the gene encoding translation elongation factor 1 alpha (TEF-1a) was amplified and sequenced (Geiser et al. 2004). The TEF-1a sequence was 597 bp long. The sequence (GenBank Accession No. KP751254) was 100% identical with sequences of F. ananatum (HE802668 and HE802666) in the NCBI database. On the basis of symptoms, pathogenicity testing, fungal morphology, and the TEF-1a region sequence, this fungus was identified as F. ananatum. To our knowledge, this is the first report of F. ananatum causing pineapple fruitlet core rot in China. This report will establish a foundation for further study of F. ananatum and effectively addressing the disease. © The American Phytopathological Society.

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