由Bipolaris zizaniae引起的文心蘭花瓣斑點病

Oncidium has become one of the most popular orchids in Taiwan in recent years. The cultivation area of oncidium cv. Gower Ramsey, used as cut flower, was over 150 ha in 1999 and was distributed mainly in the central and southern Taiwan. In the summer of 1993, a new flower disease of oncidum was found to occur at Puli and Yuche, Nantou County. The infectd petals of the orchid plants appeared small brown spots. The disease shortened the life spans of the infected cut flowers and decreased flower quality. All of the diseased orchid fields were located adjacent water bamboo (Zizania latifolia) fields, which had serious leaf blight disease caused by Bipolaris zizaniae. The diseased flowers were collected, stained with 0.5% cotton blue, and examined microscopically. In the center of each young spot, one or two germinating spores of Bipolaris species were observed. After isolation, purification, inoculation and reisolation procedures, the Bipolaris fungus was conformed to be the causal agent inducing brown spots on oncidum petals. The morphological characteristics of spores of the Bipolaris isolates from oncidum were similar to those of Bipolaris zizaniae attacking water bamboo. Two isolates of Bipolaris from each host were selected and were cross-inoculated on both hosts in greenhouse. Test isolates were cultivated on autoclaved corn-leaves for sporulation. Spore suspension approx. 5xl04 spores/ml were inoculated on oncidium petals and water boamboo leaves by aid of stilled brush. Those two Bipolaris isolates from both hosts were pathogenic to both plants and induced disease symptoms same as those appearing in the fields. Therefore, the causal agent of petal brown spot of oncidum is identified as Bipolaris zizaniae and the primary inoculum sources of the disease were considered to come from Bipolaris-infected water bamboo nearby. Besides, B. oryzae from rice, B. maydis from corn, and Bipolaris sp. from bamboo also caused similar brown spot symptoms on petals of the inoculated oncidium in pathogenicity test. Based on these results, to avoid occurrence of brown spot disease on oncidium, farmers should protect their orchid from infection by these four pathogens in advance.

並列關鍵字

Bipolaris zizaniae ； cross infection ； oncidium ； water bamboo(Manchurian wild rice)

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