Identification and Fungicide Sensitivity of Fusarium Asiaticum Causing Seedling Rot of Hinoki Cypress in a Forest Nursery in South Korea

In 2021, a seedling rot disease was observed on Hinoki cypress (Chamaecyparis obtusa) seedlings in a bareroot forest nursery in Naju-si, Jeollanam-do Province, South Korea. Infected seedlings were yellowing at the disease outset but became black after severe infection. At onset of disease, seedlings began yellowing. As disease progressed, black rot of the leaves and roots was common and eventually wilt and seedling death was observed. Seedling mortality was about 30%. The causal organism was isolated from the seedlings on potato dextrose agar media. A total of nine isolates were recovered and two representative isolates were identified as Fusarium asiaticum based on morphological characterization and phylogenetic analysis of the internal transcribed spacer (ITS) region, translation elongation factor (EF1-alpha) and RNA polymerase II (RPB2) genes. Pathogenicity and fungicide sensitivity were tested to confirm pathogen viability and control efficacy of the disease. The fungal isolate caused severe disease in the inoculated Hinoki cypress seedlings. Also, the isolates were sensitive to benomyl, hexaconazole and pyraclostrobin and showed reduced sensitivity to penthiopyrad. In planta assays showed 98.81 and 100% disease control by the application of pyraclostrobin and hexaconazole, respectively. The pathogen was re-isolated from the inoculated seedlings and its identity was confirmed by morphological analysis fulfilling Koch's postulates. The pathogen-causing disease in the Hinoki cypress is the first reported in the host worldwide.