蘭花疫病菌之生態與防治

Abstract

本文報告蘭花疫病菌Phytophthor palmivora和P. parasitica之生熊以及其防治法。 疫病在不同蘭屬引起三種不同之病徵，對蝴蝶蘭、狸狐尾蘭、文心蘭和石斛蘭引起軟腐，對萬代蘭、愛瑞地蘭和嘉德利亞蘭引起褐黑腐，對中國蘭或虎頭蘭黃化現象。 病勢進展之溫度範圍以16~36℃，最適為28℃，病斑之擴大比較適合在高標對濕度。 寄主葉片之水份潛勢與病斑之擴大程度成正相關，水分潛勢愈低病斑之擴大愈慢。 胞囊之形成溫度以P. palmivora 24-28℃ , P. parasitica 24℃。相對溫度95%時胞囊產量很多，但相對濕度85%時則無胞囊形成。高溫下(36℃)病菌在病葉組織內產生很多厚膜胞子。相對濕度90~100%時病菌在病葉表面產生很多胞囊相對濕度90~95%時病菌在萬代蘭葉片組織內產生之胞囊比厚膜胞子多，但相對濕度在80~85%時只有厚膜胞子。 胞囊可以在溫度加20~28℃，水分潛勢-1~-10 bar時直接發芽，蝴蝶蘭葉片汁液可縮短胞囊直接發芽之時間，但並不能增加發芽率，成熟胞囊可在溫度8~28℃, pH5- 8間間接發芽。 P. palmivora游走子在16~24℃間游動時間較長。pH值影響游走子游動之型式，pH 7.7時做快速直線而旋轉游動；pH 8.5時做不規則圓形游動；pH5.5時蛇行。振盪150~200轉／秒時會干擾游走子之游動。各種蘭花汁液有加速游走子靜止之功能。 游走子之發芽受下列各種處理而增加：低速振盪，改變pH值或加入蘭花葉片汁液。除木瓜葉片外所有供試寄主及非寄主汁液皆能加造游走子之發芽，萬代蘭不同部位葉片對游走子發芽之促進效果並沒有差別。 厚膜胞子之發芽溫度範圍以5~37℃，最適溫度P. palmivora 28℃，P. parasitica 24℃，在水分潛勢-1~-10 bar間厚膜胞子發芽良存，蝴蝶蘭葉片汁液。各種碳素源或氨基峻之添加並不能增加厚膜胞子之發茅。 蝸牛及蛞蝓不只直接為害蘭花，而且可以傳播蘭花疫病茵。 數種防治疫症之方法包括改進栽培環境，幼苗之照顧，化學藥劑之防治及化學療法在文中討論。 This paper reports ecology of Phytophihora palmivora and P. parasitica the causal organisms of black rot of orchids and its control. These fungi induce three types of symptoms on different genera of orchids; soft rot on Phalaenopsis, Rhyncoiylis, Oncidium and Dendrobium, black or brownish rot on Vanda, Aerides and Cafileya, and yellowing on Cymbidium. The temperature range for disease development was 16-36℃ with optimum at 28℃. The lesion enlargement was favorable at high relative humidities of near saturated. There was a good correlation between water potentials in leaves and lesion enlargement of the disease, lower the water potential of the leaves, decrease the lesion development. The temperature range for sporangia formation was 12-32℃. with optima at 24-28 ℃ for P. paimivora and at 24℃ far P. parasitica. A large amount of sporangia were formed at relative humidity 95% of no spoangia were farmed at 85%. High temperature at 36℃ was favorable for formation of chlamydospores in diseased tissues. On diseased leaves of orchids, the fungi produced abundant sporangia at 90-100% RH. In diseased Vanda leaves, the fungi produced more sporangia than chlamydospores at 90-95% RH, however, only chiamydospores were produced at 80-85% RH. Aged sporangia germinated directly under 20-28℃ at -1 - -10 bar. In the presence of leaf juice of Phataenopsis, duration required for direct germination of sporangia was shortened, however the percentage of germination was not increased. Young mature sporangia germinated indirectly under 8-28℃ at pH 5-8. Zoospore motility of P. patmivora was longer at 16-24℃. The hydrogen concentration affected the pattern of motility; straight swing with rotation at pH 7.7, irregular circular movement at pH 8.5, snaky movement at pH 5. 5. Motility of zoospores was impaired by shaking at 150-200 cycle/sec. Juice extrated from various orchids enhanced zoosp ores encystation. Germination of zoospores was enhanced by lower speed of shaking, mild change of pH values and addition of leaf juice. Juice extracted from leaves of various orchids, other host plant and non-host plants had stimulatory effect on germination of zoospores with exception of juice from papaya leaves. There was. no difference between juice extracted from old and young leaves or Vanda in stimulating germination of soospores. Chlamydospores of the fungi germinated at 8-37℃ with optimum at 28℃ for P. Palmivora and at 24℃ for P. Parasitica. Chlamydospores germinated well on media with water potential between -1 - -10 bar. Addition of Phalaenopsis leaf extract, carbon sources or amino acids did not affect the germination of chiamydospores. Helix spp. and Philomycus spp. injury on orhids not only through direct feeding, but also capable of transmission of the black rot fungi of the orchids. Several control measures are suggested here including improvement of environment for orchid cultivation, taking care of seedlings, chemical control and chemical therapy.