First Report of Fruit Rot Caused by <i>Lasiodiplodia pseudotheobromae</i> on Loquat ( <i>Eriobotrya japonica</i> ) in China

Loquat (Eriobotrya japonica Lindl.), a subtropical fruit tree native to Asia, is not only known to be nutritive but also beneficial for the treatment of diabetes in southern China (Wu et al. 2021). In May 2022, fruit rot symptoms were observed on loquat trees in three commercial orchards in Zhejiang Province, China. Soft, dark brown to black lesions with white mycelium were observed on immature and mature loquat fruit. Spotting affected 10 to 30% of loquat fruit on individual trees. To identify the causative agent, 20 symptomatic loquat fruit samples were collected and diseased portions of the fruit were cut into small pieces (4 mm×4 mm) and surface sterilized with 2.5% sodium hypochlorite for 2 min, 75% ethanol for 30 s, and rinsed three times with sterilized distilled water. The samples were plated on potato dextrose agar plates containing chloromycetin (50 mg/liter) and incubated at 25 ± 1°C in the dark for 7 days. Twenty-three identical fungal isolates were obtained from all symptomatic tissues. The isolates produced mycelium and grew rapidly, initially white, and then became gray to black after 5 d. A representative isolate DEJ-1 was purified and characterized. Conidiogenous cells were smooth, hyaline and cylindrical. Conidia were oval, dark brown with one central septum, measuring 24.4×13.2 μm on average (n=50). The culture and conidial morphology matched the description of Lasiodiplodia pseudotheobromae (Alves et al. 2008). To confirm this identification, the internal transcribed spacer (ITS), β-tubulin gene (TUB) and translation elongation factor-1 alpha (TEF-1α) regions of isolate DEJ-1 were PCR-amplified and sequenced using the primer pairs ITS1/ITS4 (White et al. 1990), Bt2a/Bt2b (Glass and Donaldson 1995) and EF1-728F/986R (Carbone and Kohn 1999), respectively. BLASTn analysis revealed the ITS sequence (ON624125) of DEJ-1 exhibited 100% similarity (521/521 bp) with L. pseudotheobromae YBUJr54 (OP412374), the TUB sequence (ON640626) had 100% identify (436/436 bp) with L. pseudotheobromae 17-003 (LC314724), and TEF-1α sequence (PX098039) showed 100% similarity (529/529 bp) with L. pseudotheobromae 17-004 (LC270869). Phylogenetic analysis based on concatenated ITS, TUB, and TEF-1α sequences grouped DEJ-1 within the clade of L. pseudotheobromae. To confirm pathogenicity, mycelium plugs of a 3-day-old colony of strain DEJ-1 were placed onto the surface of wounded mature loquat fruits (ten replicates). Wounded but not inoculated fruits were used as negative controls. The inoculated fruits were stored in a constant temperature incubator under the conditions of 25°C, 90% relative humidity, and incubated in a 12 h light/12 h dark cycle for 7 d. The symptoms on all inoculated fruit as dark brown necrotic lesions developed after 4 d, and subsequently covered the entire fruit. Symptoms were similar to those observed in the orchards, while no symptoms were observed on the negative controls. The same fungus was re-isolated from symptomatic loquat fruit and identified (three replicates), fulfilling Koch's postulates. Therefore, L. pseudotheobromae was confirmed as the causal agent of the disease. L. pseudotheobromae has been previously reported to cause disease in litchi in China (Wei et al. 2025), but this is the first report of loquat fruit rot caused by L. pseudotheobromae in China. These results provide important information for studying the epidemiology of this disease and may contribute to future studies involving disease management in loquat.