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Taiwan Agricultural Research Institute, Council of Agriculture, Executive Yuan--Publication-Journal of Taiwan Agricultural Research

Journal of Taiwan Agricultural Research

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Petal Spot of Phalaenopsis Caused by Exserohilum rostratum

Huang, C. W., J. H. Huang, J. N. Tsai, L. H. Chung, and T. F. Hsieh. 2019. Petal spot of Phalaenopsis caused by Exserohilum rostratum. J. Taiwan Agric. Res. 68(1):47–58.

Petal Spot of Phalaenopsis Caused by Exserohilum rostratum

Chiao-Wen Huang1, Jin-Hsing Huang2, Jhih-Nung Tsai2, Li-Hsiang Chung3, and Ting-Fang Hsieh4,*

Abstract

    In April 2017, flower diseases of Phalaenopsis (Sogo Yukidian ‘V3’) occurred in Tainan area with the symptoms showed brown small spots on petal, sometimes sunken, and about 1 mm or less in diameter without expanding. It seriously affected quality of ornamental flowers and cut flowers. The pathogen isolated from the diseased tissue produced dark grey mycelium on potato dextrose agar (PDA). Conidium is ellipsoidal to fusiform, dark brown, and with hilum. The causative fungus was identified as Exserohilum rostratum (Drechsler) Leonard & Suggs based on symptoms, morphological characteristics and ITS rDNA sequence. The pathogen not only harmed the white flowers of Phalaenopsis Sogo Yukidian ‘V3’, but also caused symptoms on the petals of Phalaenopsis Queen Beer ‘Mantefon’, Phalaenopsis Green Pixie ‘Ever Green’, Oncidesa Gower Ramsey ‘Honey Angel’, Cattleya Chien Ya ‘Ocean’ and Vanda Princess ‘Mikasa White’. The optimal temperature was 28℃ for mycelial growth of Exserohilum rostratum and 24–36℃ for spore germination. Mycelial growth of the pathogen was effectively inhibited more than 90% by oxine-copper, procymidone, difenoconazole and Iprodione with the concentration at 10 mg a.i. L-1. Spore germination of pathogen was inhibited by oxine-copper, copper (II) hydroxide, mancozeb and chlorothalonil with the concentration at 10 mg a.i. L-1. This is the first report of Phalaenopsis petal spot disease caused by E. rostratum in Taiwan.

Key words: Phalaenopsis, Petal spot, Fungicide screening.


* Corresponding author, e-mail: TFHsieh@tari.gov.tw
1 Assistant Research Fellow, Plant Pathology Division, Taiwan Agricultural Research Institute, Taichung, Taiwan, ROC.
2 Associate Research Fellows, Plant Pathology Division, Taiwan Agricultural Research Institute, Taichung, Taiwan, ROC.
3 Research Assistant, Plant Pathology Division, Taiwan Agricultural Research Institute, Taichung, Taiwan, ROC.
4 Research Fellow and Director, Floriculture Research Center, Taiwan Agricultural Research Institute, Yunlin, Taiwan, ROC.

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