ISHS Acta Horticulturae 665: II International Symposium on Lychee, Longan, Rambutan and other Sapindaceae Plants
BROWN ROT OF LONGAN FRUITS CAUSED BY PHYTOPHTHORA PALMIVORA IN THAILAND |
| Authors: | S. Kooariyakul, S., K. Bhavakul |
| Keywords: | pathogenicity, necrotic, tissue transplanting, zoospores, coenocytic hyphae |
| Abstract:
Brown rot of longan fruits was first observed in Mae Suai District, Chiang Rai Province, Thailand during 1998-2000. The disease started as small necrotic brown spots on fruit skin, enlarged rapidly to irregularly patches and absence of fungal hyphae on the surface of fruit skin. Often, splitting of these necrotic patches occurred after early infection. Later, the diseased fruits fell to the ground. The lesions on the surface and inner wall of the skin eventually turned to dark-brown discolouration, while the translucent flesh beneath the affected areas collapsed and turned yellowish tan. Under humid condition, the affected areas were often covered with white fungal mycelia. A Phytophthora sp. was consistently isolated from the skins of the symptomatic fruits on PDA and a selective medium, BNPRA, by the tissue transplanting method. Pathogenicity of the two representative isolates was confirmed by applying the mycelial plugs on ripening ‘Do’ longan fruits without wounding, and then soaking the fruits in zoospore suspensions (2.5 and 3.2 x 104 zoospores/ml). After two days, the fruit skins showed irregular necrotic brown lesions. The symptom on artificial inoculated fruits was similar to natural infection. The fungus was identified as Phytophthora palmivora (Butl.) Butl. MFl based upon some physiological and morphological characteristics. | |
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