Identification of stem blight of caused by in China.

, commonly known as Sprinkled coral due to its golden-yellow spotted leaves, is a widely utilized plant in Chinese landscaping. In September 2023, severe symptoms of stem blight were observed on grown in a 0.45-ha field in Kunshan City, Jiangsu Province, China (36°61'44″ N, 134°52'59″ E), with an incidence rate of 13% (n=100). The disease manifested predominantly on the stems and branches of the plant. Initially, circular or irregular black necrotic spots appear on the branches, which gradually expand and lead to the branches and stems wilting. To isolate the causal agents, six plants exhibiting typical symptoms were collected from the field, and three 5 × 5 mm infected tissue sections were taken from each plant. The sections were surface-disinfected in 75% alcohol for 30 seconds, followed by 3% sodium hypochlorite for 2 minutes, and rinsed three times with sterile distilled water. After air-drying on sterile filter paper under aseptic conditions, a total of 18 sections were cultured on Potato Dextrose Agar (PDA) and incubated at 25℃. After 3 days of incubation, single hyphal tips were transferred to fresh PDA media for purification. The initially white aerial mycelium changed to a black-gray coloration within 3 to 6 days on PDA plates. Additionally, the formation of globose pycnidia was observed after 2 weeks of growth on Water Agar plates. The conidia were hyaline, fusiform, with a subobtuse apex and a truncate base, measuring 15.65 to 24.43 × 5.35 to 8.74 μm in length and width respectively. All 18 isolates obtained exhibited consistent phenotypic characteristics. Based on these morphological features, the isolates were consistent with sp. (Pavlic et al., 2007). Three isolates (2024YKY1 to 3) were selected for molecular identification. PCR was performed on extracted DNA to amplify the ITS region and the translation elongation factor 1-alpha (EF1α) gene using the universal primers ITS1/ITS4 (White et al., 1990) and EF1-728F/EF1-986R (Carbone and Kohn, 1999), respectively. The ITS and EF1α sequences were deposited in GenBank (accession number PP389880 to PP389882 for ITS, PP429376 to PP429378 for EF1α), showing 99% to 100% (492/493 bp for ITS, 293/293 bp for EF1α) homology with Bot02 (accession number MG745827 and MG745818). A phylogenetic tree constructed from concatenated ITS and EF1α sequences using the Maximum Likelihood (ML) model confirmed that the isolates belonged to the clade. For pathogenicity testing, 20 healthy plants were selected, and their stems were carefully wounded with a sterilized hypodermic needle. Among these, 15 plants were inoculated with 10 µL of conidial suspension (10 conidia/mL) from the selected isolates (five plants per isolate), while five control plants were treated with 10 µL of sterile distilled water. All plants were placed in a greenhouse maintained at 26 ± 2℃. Black spots developed at the inoculation sites on treated plants 6 days post-inoculation, closely resembling the symptoms observed under natural conditions. In contrast, the control plants remained asymptomatic. To fulfill Koch's postulates, the causal pathogens were re-isolated from the inoculation sites and confirmed as based on morphological characteristics. It is noteworthy that the present study reports for the first time on the occurrence of induced blight of in China, providing a foundation for future disease management.