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Rosa roxburghii Tratt is a plant from the Rosaceae family whose fruits are rich in vitamins, dietary fiber, flavonoids, phenolic acids, and other active components (Jiang, et al. 2024). In July 2023, about R. roxburghii 500 plants were investigated in a field of 6000 m2 in Guiding County (107°14'E, 26°45'N), Guizhou province, China, and the results showed a leaf spot incidence of s 20 to 30%. The affected leaves had irregular, black lesions with a clear blackish brown boundary and faint black conidiomata in a brown center. Fifteen symptomatic leaves were collected from 10 plants washed with sterile distilled water, and 5 × 5 mm pieces of the infected tissues were cut. After surface sterilization for30 s with 75% ethanol, 2 min with 3% NaOCl, three washes in sterilized distilled water, the leaf pieces were dried and placed on potato dextrose agar (PDA) and incubated at 25℃ for 5 days. Three isolates (H3-Y-1-1, H3-Y-1-2, H3-Y-1-3) with identical morphology were obtained, and the isolate H3-Y-1-1was selected for further study. The colonies on PDA exhibited irregular growth patterns, with white felty aerial mycelium on the upper surface, and white mycelium on the lower surface. Conidiomata were irregularly distributed over the agar surface. The isolate H3-Y-1-1 produced darkly pigmented pycnidia on PDA after 30 days and oozed milky mucilaginous drops. The fungus produced two types of conidia, α and β. Regular α conidia were 4.74 – 5.96 × 1.52 – 2.24 μm (n = 50), hyaline, elongated, biguttulate and non-septate. Beta conidia were 20.13 – 25.74 × 0.86 – 1.29 μm (n = 50), aseptate, hyaline, smooth, spindle shaped, slightly curved to bent. The morphological features were consistent with the description of Diaporthe eres (Pereira, et al. 2022). The pathogen was confirmed to be D. eres by amplification and sequencing of the internal transcribed spacer region (ITS), the partial β-tubulin (TUB), the partial translation elongation factor 1-alpha (TEF) genes using primers ITS1/ITS4, Bt-2a/Bt-2b, EF1-728F/EF1-986R, respectively. Sequences from PCR amplification were deposited in GenBank with accession numbers PP411998 (ITS), PP502153 (TUB), PP502156 (TEF). BLAST searches of the sequences revealed (96%) (500/523nt), 97% (479/494 nt) and 99% (334/338 nt) homology with those of D. eres CBS 138594 from GenBank (OM698848, OM752196 and OM752197), respectively. Phylogenetic analysis using maximum-likelihood and Bayesian methods placed the isolate H3-Y-1-1 in a well-supported cluster with D. eres CBS 101742. The pathogen was thus identified as D. eres based on the morphological characterization and molecular analyses (Feng, et al. 2013; Tao, et al. 2020). To assess its pathogenicity, healthy R. roxburghii potted plants were inoculated with H3-Y-1-1 spore suspensions. Symptomatic leaves mirroring field symptoms were observed after XX days of incubations at XX°C, while control plants exhibited no symptoms. Diaporthe eres was consistently reisolated from the infected leaves showing brown irregular or round lesions at the initial stage of the disease, expanding and become more irregular over time ultimately causing leaf curling and plant death. To our knowledge, this is the first report of leaf spot on R. roxburghii caused by D. eres in China. The disease may become a serious threat to fruit of R. roxburghii production in China. Therefore, detection of this pathogen is very important to ensure timely disease management.
Jia et al. (Tue,) studied this question.