美葉蘇鐵疫病

Abstract

西元二○○一年六月至七月問南投草屯蘇鐵育苗場種植之美葉蘇鐵(Zamia furfuracea)發生嚴東枯死情形。罹病植株葉片黃化、根系腐敗、莖部組織褐化，嚴車時全株枯萎死亡。經組織分離獲得3株疫病菌，將該疫病菌之游走子懸浮液接種蘇鐵幼苗根部，一個月後引起接種根部腐敗，並由罹病處分離得接種疫病菌，證明蘇鐵幼苗腐敗係因疫病菌引起。獲得之疫病菌的特性為：在馬鈴薯葡萄糖培 養基(PDA)上形成玫瑰花瓣狀之圖形；菌絲在8-32℃下可生長，最適生長溫度為24-28℃；胞囊須經土壤抽出液或礦物鹽液漂洗後才會形成，胞囊橢圓形、長橢圓形，不具乳突(non-papilate)亦不脫落，胞囊釋放游走子後會再生內生或串生胞囊；形成珊瑚狀菌絲膨脹體及厚膜胞子；配對型為A1，可刺激A2型之Phytophthora parasitica形成卵胞子，但本身無卵胞子產生；經鑑定為Phytophthora cinnamomi Rands。P. cinnamomi危害蘇鐵為世界首度報導。 Serious seedling decline of Zamia furfuracea was found at Tsaotuan, Nantow in the summer of 2001. The leaves of the affected seedlings became smaller and yellow at the early stage and their root systems were necrotic and seriously rotted. The internal tissues of affected stems turned brown and soft with gummosis. The diseased plants grew slowly and died eventually. Three isolates of Phytophthora were isolated and all of them caused disease symptoms similar to those appearing in the field on the inoculated young seedlings. The same fungi were reisolated from the inoculated diseased seedlings. The isolated Phytophthora grew on V-8 agar at temperature ranging from 8-32 with the optimum temperatures of 24-28 . The fungal colonies showed rosette pattern on PDA plates. Hyphal swellings were spherical, irregular to coralloid, clustered or single. Sporangia were not formed on agar plates but were produced abundantly in soil extract solution or washed with mineral solution. Sporangia, 42.5-(53.5)-65.0 27.5-(32.1)-35 m, were non-papillate and non-deciduous, and displayed nested and extended proliferation in water. The ratios of L/B were 1.21-(1.67)-2.7. Chlamydospores, 25-(31)-35 m, were spherical and thin-walled. All of the three Phytophthora isolates belonged to A1 mating type. None of them form oospores themselves when paired with A2 type of P. parasitica. However, they were able to stimulate A2 to initiate sexual reproduction. The Phytophthora was identified as Phytophthora cinnamomi Rands according to Waterhouse' key. This is the first report of Phytophthora disease of Zamia furfuracea in Taiwan as well as in the world.