探討亞磷酸對疫病菌侵染過程的影響

疫病菌屬(Phytophthora)被歸類於雜色藻界卵菌綱，包含多種危害猖獗的土壤傳播性病原菌，常對作物經濟產量及品質造成嚴重鉅害。亞磷酸(Phosphite)為針對卵菌類病害有良好效果的非農藥防治資材，受到廣泛運用，但關於亞磷酸的詳細作用機制仍待深入探討。為瞭解亞磷酸對疫病菌感染植物過程的影響，本研究觀察表現綠螢光蛋白的疫病菌Phytophthora parasitica (菌株代號1121)在以中和後亞磷酸(neutralized phosphorous acid; NPA)預處理之圓葉菸草(Nicotiana benthamiana)的感染情形，發現接種後 18小時，NPA 處理組及水處理控制組皆出現明顯病徵；接種後 24 小時，控制組的病斑面積和生物量都明顯比多於NPA 處理組，顯示 NPA 處理能增加菸草對疫病菌的抗病能力。以疫病菌游走子接種於NPA-預處理的菸草葉片50–70 分鐘後，靜止子平均發芽率約 31.3% ± 5.8%，相對的，控制組靜止子平均發芽率為 50.5% ± 9.4%。接種後 24至 30 小時，觀察每平方毫米菸草葉片形成孢囊的數量，發現會因 NPA的處理而受到抑制，並且有所延遲，但 NPA 處理對疫病菌在菸草的壓器形成率、菌絲分支以及壓器、吸器和孢囊等重要侵染構造的外觀皆未造成影響。另外， NPA 處理能有效促進菸草葉片癒傷葡聚醣(callose)的累積以及提升感染初期植物活化氧族(reactive oxygen species; ROS)的產生量。

關鍵字

疫病菌；亞磷酸；中和後亞磷酸；疫病菌侵染過程

並列摘要

The genus Phytophthora belongs to Oomycota, Chromista. Many species in this genus are notorious soil-borne plant pathogens, which cause economical losses and serious threats to food security worldwide. Phosphite is a well-known non-pesticide for effective control of Phytophthora blight. However, the mechanism of phosphite action is not fully elucidated. The purpose of this study is to know how phosphite impairs the development of disease caused by Phytophthora parasitica, which causes severe diseases in a wide variety of plant species. When tobacco (Nicotiana benthamiana) leaves were inoculated with green fluorescent protein (GFP)-expressing P. parasitica (strain 1121), disease symptoms appear on the leaves of both control and neutralized phosphorous acid (NPA)-pretreated plants at 18 h post inoculation. At 24 h post inoculation, the lesions in control leaves were bigger than those on NPA-treated leaves. When inoculated with zoospores of P. parasitica (1121), only about one third of cysts (31.3% ± 5.8%) germinated at 50-70 min post inoculation in NPA-pretreated leaves, whereas 50.5% ± 9.4% of cysts germinated in water-pretreated control leaves. The number of sporangia per square millimeter on tobacco leaves was reduced by NPA from 24 h to 30 h post inoculation. The results showed that the differentiation of sporangia in NPA-treated leaves was postponed. However, there was no effect of NPA on the rate of appressoria formation, hyphal branching, nor on the appearance of appressoria, haustoria, and sporangia of P. parasitica. Nevertheless, NPA induced callose deposition as well as reactive oxygen species (ROS) accumulation.