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Circular Spot of Sweet Potato Caused by Sclerotium rolfsii in Taiwan
Circular spot symptom (arrow) of naturally infected storage root of sweet potato ‘TN57’ (A) and white to brown sclerotia production on the field soil (B). Colony of <em>Sclerotium rolfsii</em> SCL-003 isolate cultured on PDA showing white mycelium and dark brown sclerotia (C). Clamp connection (arrow) of hyphae in <em>Sclerotium rolfsii</em> SCL-003 cultured on 1.5% WA for 2 days (D).
Circular spot symptom (arrow) of naturally infected storage root of sweet potato ‘TN57’ (A) and white to brown sclerotia production on the field soil (B). Colony of Sclerotium rolfsii SCL-003 isolate cultured on PDA showing white mycelium and dark brown sclerotia (C). Clamp connection (arrow) of hyphae in Sclerotium rolfsii SCL-003 cultured on 1.5% WA for 2 days (D).

Author:Chiao-Wen Huang, Hong-Ren Yang, Ching-Yi Lin, Sui-Li Hsu, Su-Yu Lai, Wen-Chi Ko, and Hui-Fang Ni*

Abstract:

    In 2015, a severe disease outbreak on sweet potato storage root with the symptoms of circular yellowish brown to brown lesions occurred in Chunghua, Yunlin, and Pingtung areas. The pathogen isolated from the diseased tissue had white mycelium, clamp connection, and it produced brown sclerotia, which was identified as Sclerotium rolfsii Sacc. based on these morphological characters and ITS sequence. The growth temperature of pathogen isolates ranged from 15 to 35℃, and the optimum growth temperature was 30 ℃. The pathogen isolate, SCL-003, showed pathogenic ability on sweet potato storage roots and seedlings. Nine fungicides were selected for evaluating the inhibition effect on mycelial growth of two pathogen isolates (SCL-001 and SCL-003). The results showed that the effective fungicides with more than 89% inhibition rate were 50% flutolanil, 75.0% mepronil, 7.5% epoxiconazole, 23.0% hexaconazole, and 25.0% pencycuron + tebuconazole with 10 mg a.i. L-1 dilution concentration. This is the first report of circular spot disease on sweet potato caused by Sclerotium rolfsii in Taiwan.

Key words:Sweet potato (Ipomoea batatas), Circular spot diseases, Fungicide screening

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Journal of
Taiwan Agricultural Research
Vol. 73, No.1 (2024) ISSN: 2790-086X Vol. 73, No.1 (2024)
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