寄生性綠藻「台灣產Stomatochroon sp.」之生態調查及其習性、形態之研究

Abstract

本報告??述寄生性綠藻台灣產Stomatochroon sp.對單株寄主感染程度與氣象因數（如：溫度、相對濕度、輻射量，降雨量和風速）的關係，及其習性、形態和藻斑及感染過程，以及此藻寄生前後，寄主組織形態之變化。 Stomatochroon sp.比同科（橘色藻科）中的其他各屬（如：橘色藻屬、頭孢藻屬和葉楯藻屬），其形態最?簡單，台灣產Stomatochroon sp.在台灣屏東地區被發現，內寄生於熱帶經濟果樹蓮霧Syzygium samarangense (Blume) Merr & Perry之葉片下表面，但在其他各器官或他種植物體上並未發現。實地調查其自然生態特況及利用解剖，一般光學顯微鏡及掃描式電子顯微鏡觀察顯出，台灣產Stomatochroon sp.之感染率，經年高達100％，對單株寄主之感染程度亦非常嚴重，且具消長之現象。此種消長現象似與氣象因數的改變有關。當溫度稍高(24－28℃)，高相對濕度（80％以上），輻射量(300-400 Cal/cm2/day)，高降雨量（?雨季時）和稍高風速(1M/Sec左右)，都可能有助於此藻之發生或生長。 台灣產Stomatochroon sp.之藻體，最初皆由存在於氣孔內側之中心細胞發育而來，藻體分?二部分：一?次氣生藻體，係由棲息於氣孔室內之中心細胞和固著細胞以及寄主海綿組織間隙內的分枝絲狀體所組成，以上亦稱?營養體。通常這藻體?薄壁，含葉綠素而呈現出淺綠或深綠色。分枝狀之絲狀體在環境不良時，潛伏在寄主組織間隙內，俟環境適當時，再由其頂端細胞發育成中心細胞，進而長出新的氣生藻體。二?氣生藻體，乃指曝露於寄主體外生長者，包括直立的不孕性之凸起物，遊走孢子囊枝和配子囊。氣生部分由於含有多量血色素，而顯現出黃褐色或紅褐色，其顏色之轉變似與其藻體之成熟度有關。台灣產Stomatochroon sp.的遊走孢子囊枝，是一種直立多細胞之絲狀體，由頭狀細胞、柄細胞和遊走孢子囊所組成。在無性繁殖時期，首先由表面有顆粒狀之中心細胞產生一個頭狀細胞，再由頭狀細胞形成一至三個（一個者居多）彎曲之柄細胞，每個柄細胞長出一個頂生之遊走孢子囊。成熟的遊走孢子囊枝中頭狀細胞和柄細胞外壁平滑，而浮走孢子囊?球形，外具顆粒狀突起及一明顯之塞狀遊走孢子釋放孔，藉此孔可釋出8－32個（多?16）具有二或四根等長頂生鞭毛的遊走孢子。配子囊?此藻有性生殖期所形成之藻體，由一表面平滑或具層狀重疊而周邊皺褶的中心細胞所產生，通常一至四個著生在此中心細胞之頂部或周圍，其間有明顯之橫壁，但不產生離層隔板。成熟之配子囊?似羽狀，無柄，有一明顯的塞狀配子釋放孔。8-64個（通常?32）前端祇具二根等長鞭毛之配子藉此孔釋放。所有的動細胞含葉綠素，呈現綠色，但不具眼點。 台灣產Stomatochroon sp.之藻斑，乃由氣生藻體部分所構成，因常顯現出黃褐或紅褐色，?肉眼可辨。其感染之過程，乃藉風、雨和昆蟲?媒介。在感染初期，寄主之葉緣和葉尖處先出現藻斑，隨著生長，藻斑呈現不規則狀分佈於寄主葉片下表面各處。感染末期時，藻斑呈現褐色，且寄主葉片出現黃化現象。此藻感染後，初、中期之寄主組織切片觀上並無多大變化，但晚一末期時，寄主海綿組織有明顯之變形曲扭。儘管於感染晚一末期間，寄主組織有顯著變化，但並未發現台灣產Stomatochroon sp.之任何藻體穿入寄主組織細胞內生長。

The present investigation deals with the relationship between disease incident degree to host and climatic factors (i.e. temperature, relative humidity, glosal solar radiation, precipitation and wind speed). The habit, morphology, algal spot and infectious process of parasitic green alga-Stomatochroon sp. in Taiwan and the morphological changes of host tissue during the infection were also described. As compared with the other members of the Trentepohliaceae (i. e. Trentepohlia, Cephaleuros and Phycopeltis), Stomatochroon seems to be the most reduced one in plant body. Stomatochroon sp. in Taiwan has been found in Ping-Tung area in Taiwan. It is endophyte on the lower surface of leaf of tropic economical fruiter Syzygium samarangense (Blume) Merr Perry, but neither the other organs of the same plant nor the other plants. The ecological survey, dissecting-, compound-and scanning electron microscopies indicate that the disease incident rating of Stomatochroon sp. in Taiwan is perennially up to 100%. The disease incident degree of single host is very serious. The fair degree of infection seems to be correlated with some climatic factors, such as: higher temperature (24-280C), higher relative humidity (more than 80%), glosal solar radiation (300-400 Cal/cm2/day), higher precipitation and higher wind speed. There are two growing phases in its thalli: 1) subaerial thallus (or vegetative thallus), and 2) aerial thallus. The former is composed of central basal cell or/and anchor cell that inhabit in the substomatal chamber and the branching filament which is formed in intercellular space of spongy tissue of host. The latter consists of erect sterile trichome (or trichomes) and reproductive structures (including zoosporangiophore and gamatangium). The subserial thallus is always green in color, whereas its aerial part shows rich haematochrome content in their cell, consequently they appear to be yellowish brown to reddish brown. The indication of the first entrance of the algal cell is happened to be stoma in lower epidermis of host leaf. The branching filament seems to be represent an over-winter stage and would produce new fertile thallus under favorable enviromental condition. The zoosporangiophore is uniseriate multicellular erect filament which includs head cell, suffultory cell and zoosporangium. Prior to the formation of sporangium, a head cell is formed from the central basal cell which is papillate on the surface. The head cell produces one to three (usually one) suffultory cells. Each suffultory cell bears one terminal zoosporangium. The mature zoosporangium has a pluged escape pore, with papillate outerwall, but both the head cell and the suffultory are smooth. Of 8-32 (usually 16) zoospores are discharged from the escape pore when the zoospprangium matures, Both bi-and quadriflagellagellate zoospores are found. They are anterior and equal in length. When sexual reproduction occurrs one to four gametangia are prodeced from the central basal cell which is smooth or folded on the surface. The mature gametangium is puffball-like with smooth outerwall and possesses a conspicuous pluged escape pore. Of 8-64 (usually 32) gametes are formed. Only anterior biflagellate gametes are found. All the motile cells are green, lack eyespots The algal spots can be distinguished by nacked eye due to their color. The process of infection is by means of wind, rain and insects. As the alga grew, the algal Spot appear first on the drip tip and margin of host leaf, then the spots spread randomly on the lower surface of the host leaf. In both the early and the middle stages of infection, the cells in host tissue kept their original morphology in outline as seen under LM. But in later stage, the spongy cells become irregularly shringed or distorted. However the algal strands did not invade the interior of mesophyllous cells but stayed intercellularly.