Occurrence of Postharvest Fruit Rot of Mango Caused by Fusarium pernambucanum in China.

Abstract

Mango (Mangifera indica L.) is one of the most important tropical fruits in the world, thanks to its pleasant taste, aroma and high nutritional value (Ibarra et al. 2015). In June 2021, Surveys were conducted in three agricultural markets (113°36'E, 23°11'N) of the Yuancun district in Guangzhou, China. Postharvest fruit rot was observed on mango (about 25% of the fruits showed disease symptoms). Black rot symptomatic lesions were observed on the fruit surface and eventually penetrated the mesocarp of mango fruits. To isolate and identify the pathogen, fruits (n=35) were surface disinfected with 1% NaOCl (1 min), 70% ethanol (30 s) and then washed twice with sterile distilled water. Thirty small pieces (3-5 mm2) were excised from the lesion margins. The excised tissue pieces were cultured on potato dextrose agar (PDA). Pure cultures were obtained by transferring hyphal tips onto fresh PDA. Fungal isolates XTM-5 and XTM-8 were isolated from diseased fruits. All isolates grown on PDA had abundant, fluffy, whitish to yellowish aerial mycelia, and the colony reverse was pale brown. Macroconidia were falcate, slightly curved with 5-7 septa, 29.5-42.2 × 4.3-6.2 μm. Spindle-shaped mesoconidia were abundantly produced, straight to slightly curved with 3-4 septa, 20.3-24.5 × 4.6-4.8 μm. Microconidia were pyriform to obovate with 0-2 septa, 7.3-11.7 × 2.4-3.2 μm. Chlamydospores were globose or irregular, in chains and, hyaline to light brown. Based on the morphological characteristics, the fungus was tentatively identified as Fusarium pernambucanum (Santos et al. 2019). The molecular identity of the isolates was confirmed by sequencing the internal transcribed spacer (ITS), translation elongation factor 1 alpha (TEF1) and RNA polymerase subunit II gene region (RPB2) genes (White et al. 1990; O'Donnell et al. 2022). Sequences of isolate XTM-8 were deposited in GenBank (ITS: ON413679.1, TEF1:ON420221.2, RPB2: ON420222.2). A maximum-likelihood phylogenetic tree based on the concatenated sequences confirmed the isolates as F. pernambucanum (Xia et al. 2019). A pathogenicity test was conducted on mango. Six healthy fruits were inoculated with F. pernambucanum mycelial discs (5 mm in diameter) after being wounded with a needle or unwounded, six control fruits were inoculated with PDA agar. All inoculated fruits were incubated in the dark at 26°C and 95% relative humidity for 7 days post inoculation. Control fruits remained asymptomatic, whereas inoculated fruit developed symptoms on the fruit surface at the point of inoculation. The pathogenicity test was performed three times. The original isolates were confirmed morphologically and molecularly after they were reisolated from the symptomatic fruit, thus confirming Koch's postulates. F. pernambucanum is a widespread pathogen that causes diseases across a wide range of plant hosts in China, such as muskmelon fruit rot (Zhang et al. 2022); mango leaf spots (Guo et al. 2021) and plum leaf blight (Lu et al. 2022). To our knowledge, this is the first report of F. pernambucanum causing fruit rot of mango in China. As mango contamination with Fusarium mycotoxins poses a health risk for consumers, the occurrence of this disease needs to be carefully monitored to ensure effective disease management strategies are implemented in mango production.