Journal of Taiwan Agricultural Research

Author:Chiao-Wen Huang*、Jin-Hsing Huang、and Ting-Fang Hsieh

Abstract:

Fleck spot disease is critical for oriental cymbidium cultivation owing to decreasing the appearance quality of plants. The main symptom is circular or irregular fleck lesions in black to brown on young leaves with or without a yellowish halo around the lesions. Occasionally in severe disease conditions, young shoots showed browning rot of basal leaves and shoot death. A species of fungus was isolated from the diseased tissue and identified as Fusarium proliferatum based on morphological characters, nucleotide sequence comparison of internal transcribed spacer (ITS), and translation elongation factor 1 alpha (TEF-1α) gene. Pathogenicity tests were carried out by artificial inoculation with conidial suspensions of the tested fungus to fulfill Koch’s postulates. The optimal temperatures for mycelial growth and spore germination of F. proliferatum were 24−28℃ and 20−32℃, respectively. Seven oriental cymbidium cultivars including Cymbidium ensifolium, C. sinense and C. goeringii, showed brown-to-black fleck lesions on young leaves, but no symptom appeared on mature leaves after artificial inoculation. To investigate the effect of shoot age on the susceptibility of fleck spot disease, potted oriental cymbidium (C. ensifolium ‘Tsai-hong’ cultivar) contained different ages of shoots were inoculated with conidial suspension at 28℃. Results showed that disease severities of 0.5, 1.0, 1.5, 2.5, 3.5 and 4.5-month-old of shoots were 58.3−59.3%, 52.8−62.5%, 29.2−49.3%, 13.9−25.9%, 2.8−14.6% and 0%, respectively; whereas the adult shoots showed no fleck spot symptoms. The above results might provide the information for controlling fleck spot of oriental cymbidium caused by F. proliferatum. 

Key words: Oriental cymbidium, Fleck spot, Fusarium proliferatum.

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