First Report of Neoscytalidium dimidiatum Causing Fruit Rot on Fig in China.

Abstract

Fig (Ficus carica L.) holds economic significance in Atushi, Xinjiang, but as fig cultivation expands, disease prevalence has risen. In July 2024, approximately 22% of harvested fig (cv. Xinjiang Zaohuang) from 20 commercial orchards (covering 40 hectares) in Atushi (39°39'37.65" N, 76°14'3.62" E) showed varying degrees of fruit rot symptoms. The initial symptoms were characterized by the appearance of small, brown lesions on the fruit surface. These lesions rapidly progressed into water-soaked spots, which expanded quickly. As the disease advanced, the affected areas became covered with dense, white, fluffy mycelia, accompanied by prominent black sporulation. In later stages, the infected tissues softened further, ultimately resulting in the complete decay of the fruit. Twenty diseased fig were collected from the sampling site. Tissue samples (5×5×5 mm) were cut at the diseased-healthy junction, surface-sterilized in 0.5% NaClO for 1 minute, rinsed twice in sterile distilled water, air-dried, and transferred aseptically onto potato dextrose agar (PDA), and incubated at 25°C for 5 days with a 12-hour photoperiod. Fifteen isolates were obtained from the infected tissues, with two representative isolates (WH 12 and WH 23) selected for further study due to morphological similarity. The fungal colonies initially appeared as white mycelium, later turning olive green to grayish-black. Colony growth was rapid (32 mm/day). Arthrospores were colorless to light brown, short columnar, aseptate, with a truncated base, 0 to 1 septate, averaging 11.9±2.3×3.6±0.8 μm (n = 50), and sometimes formed arthric chains. Chlamydospores were dark brown, round or oval, 0 to 1 septate, averaging 7.26±1.7×5.05±1.0 μm (n = 50). Genomic DNA was extracted from the two isolates. The internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF1-α), and beta-tubulin (TUB2) genes were amplified using primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone & Kohn. 1999), and BT2a/BT2b (Glass & Donaldson. 1995), respectively, and sequences were deposited in GenBank (ITS: PQ555020, PQ555021; TUB2: PQ557519, PQ557521; TEF1-α: PQ557520, PQ557522). BLAST analysis revealed 99-100% similarity to Neoscytalidium dimidiatum Arp2-D (ITS: MK813852; TUB2: MK816354; TEF1-α: MK816355). Phylogenetic analysis using IQ-Tree and MrBayes3.2.7 based on concatenated ITS-TEF1-TUB sequences showed WH 12 and WH 23 clustering with N. dimidiatum Arp2-D (99% bootstrap). Morphological and molecular data identified the isolates as N. dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). Pathogenicity tests were conducted on 20 healthy fig (cv. Xinjiang Zaohuang) by inoculating each fruit with 10 µl of a WH 12 conidial suspension (1 × 10⁶ conidia/ml) using sterile needles. The Control were treated with 10 µl of sterile distilled water. All fruits were placed in sterile plastic containers and incubated at 25 ± 1°C, 90% relative humidity, and a 12-hour light cycle. This experiment was performed twice. On the 1st day post-inoculation, brown lesions began to develop on the fruit. By the 4th day post-inoculation, the entire fruit was completely decayed and covered with white mycelia and black spores, while the control fruit showed no symptoms. The fungus was successfully reisolated from the inoculated fruits and identified as N. dimidiatum following the methods described above, fulfilling Koch's postulates. N. dimidiatum has been reported to have a wide range of hosts in China, such as Jacaranda mimosifolia, Hylocereus megalanthus, Hylocereus undatus, and Styphnolobium japonicum (Li et al. 2024; Zeng et al. 2024; Lan et al. 2022; Luo et al. 2024). To our knowledge, this study is the first report of N. dimidiatum as the causal agent of fruit rot in fig in China. Our findings have expanded the host range of N. dimidiatum in China and provide a theoretical basis for the diagnosis and treatment of the disease.