Cathaya argyrophylla Chun et Kuang is a tertiary relict plant unique to China, with important scientific and practical value, and is a Class I key protected wild plant in China (Qian et al., 2016; Qu et al., 2018; Yang et al., 2020). In June 2025, during a field study in the Dashahe National Nature Reserve (107.6 E, 28.89 N) in Daozhen County, Guizhou Province, leaf spot symptoms were observed on C. argyrophylla for the first time. As a core distribution area of C. argyrophylla, the Dashahe National Nature Reserve in Guizhou Province has a distribution area of approximately 8.81 hectares, with a total of 866 C. argyrophylla trees. According to the survey, 217 trees were affected by leaf spot disease, with a disease incidence rate of about 25%. Symptoms appeared as irregular necrotic lesions on infected leaves, reddish brown with dark brown margins, gradually expanding. Ten symptomatic leaves were collected. Tissue segments (5 × 5 mm) cut from lesion margins were surface-disinfected in 75% ethanol for 30 s, then in 3% sodium hypochlorite for 2 min, and rinsed three times with sterile distilled water. Hyphal tips were transferred to PDA and incubated at 28 ℃ for 7 days. Three single-spore isolates (YB-1, YB-2, LE-1) were obtained, showing identical morphological characteristics. DNA was extracted, and the ITS region was amplified using ITS1/ITS4 (White et al. 1990). Results confirmed that YB-1, YB-2 and LE-1 belong to the same species, Diaporthe eres. YB-1 was selected as the representative strain. After 3–5 days on PDA, colonies showed slightly raised centers with dense white mycelium. After 7 days, mycelium turned from white to light gray, with distinct radial growth. Colony margins were indistinct, villous, with white granular protrusions. Spherical to subspherical black conidiomata were embedded in the white mycelium. Alpha conidia are unicellular, translucent, fusiform, and measure 9.2 to 10.6 × 5.4 to 6.3 µm (n = 50). Beta conidia were hyaline, aseptate, filiform, hamate, and 9.05 to 33.12 × 0.5 to 1.2 µm.（n = 10). For molecular identification, total genomic DNA was extracted. The complete internal transcribed spacer (ITS), translation elongation factor-1 alpha (TEF1), and calmodulin (CAL) regions were amplified and sequenced using primers ITS1/ITS4 (White et al., 1990), EF1 728F/EF1-986R, and CAL-228F/CAL 737R (Carbone and Kohn, 1999), respectively. The ITS, TEF1, and CAL sequences were obtained and deposited in GenBank under accession nos. PX999695, PZ094119, and PZ094118, respectively. BLAST searches in GenBank showed 100% identity with Diaporthe eres GH06. Phylogenetic analysis further confirmed that the isolate clustered within a well-supported clade with D. eres. Pathogenicity tests were conducted using isolate LE-1 on three 2-year-old C. argyrophylla plants. Per plant, three leaves were inoculated with spore suspension (10⁶ conidia/mL); three control plants received sterile water. Incubation: 25℃, 12-h photoperiod, 75% relative humidity. Experiment repeated three times. At 14 days post-inoculation, inoculated leaves showed reddish brown lesions (similar to field symptoms); controls were asymptomatic. The fungus was re-isolated from symptomatic leaves and identified by morphological and molecular methods, fulfilling Koch's postulates. This is the first report of leaf spot on Cathaya argyrophylla in China, providing a basis for disease control strategies and understanding of pathogen effects on host health.
Yang et al. (Mon,) studied this question.