First Report of Flower Rot Disease Caused by Cladosporium tenuissimum on loquat ( Eriobotrya japonica L.) in Shanghai, China

Loquat (Eriobotrya japonica Lindl. family Rosaceae), is an evergreen subtropical economic fruit tree native to Southwest China. Unlike other rosaceous species, loquat typically flowers in autumn and early winter (Wang et al., 2025). In Shanghai, China, loquat blooms from November to the following February, which is often accompanied by rainy and freezing weather (An et al. 2021). Low temperatures combined with high humidity predispose loquat flowers to fungal invasion, causing flower rot. The pathogens quickly colonize the petal surface, producing a dense grayish-green or black mold that induces tissue browning, wilting, and decay. Affected flowers either drop off prematurely or dry out and remain shriveled and attached to the branches, substantially reducing fruit yield and quality (Wang et al. 2025). The flower rot of loquat occurred severely during December 2025 to January 2026 in loquat orchards in Zhuanghang Town, Fengxian District, Shanghai City of China. The incidence rate was generally 50% in the cultivar ‘Qixing’. Infected flowers had grayish-green or black moldy layer growing on the surface of the stigma. The infection spreads downward from the stigma through the entire flower receptacle and pedicel, causing the whole flower to turn brown, wilt, rot, and eventually drop off or hang dry and shriveled on the branch. Six symptomatic flowers were collected. Diseased flower pieces were surface sterilized with 70% ethanol for 2 to 3 min, rinsed with sterile distilled water three times, and placed on potato dextrose agar (PDA) medium at 25℃ in darkness. A total of four fungal isolates with similar morphology were obtained from the infected samples. Purified fungal colonies at the age of 3 days, dark green to black, with white regular edges and olive at the reverse. The conidial size was 3.58 to 6.51 × 2.01 to 3.72 μm. The fragments in the ITS and ACT regions of the fungal rDNA, were amplified using the primers ITS1/ITS4 and ACTF/ACTR (White et al. 1990; Carbone and Kohn 1999). The DNA sequences obtained from all four isolates were identical. The resulting ITS (PZ654928) and ACT (PZ669366) sequences from representative isolate LOF01 were 99 to 100% identical to the C. tenuissimum accessions (ITS: MH712173; ACT: MF474134). The pathogenicity test was performed with conidia of a 14-day-old culture, sprayed at a final concentration of 1 × 106 conidia/mL on eight flowers of five plants. For the control group, the same volume of sterile distilled water was sprayed onto three flowers of two plants. The inoculated flowers were covered with plastic bags, which were removed 2 days post-inoculation. The inoculated plants were maintained in the greenhouse with automated temperature and humidity control at 20℃± 2 ℃ and 75±5% relative humidity throughout the experiment. Disease symptoms were recorded 10 days after inoculation. The inoculated flowers exhibited symptoms similar as those previously observed, characterized by distinct grayish-green or black mold, whereas no symptoms were observed on control flowers. The fungus reisolated from symptomatic inoculated flowers was morphologically and molecularly identified as C. tenuissimum. This fungus has been previously reported to cause tea plant diseases in China. (Lv et al. 2014). To our knowledge, this is the first report of C. tenuissimum causing flower rot on loquat in China.