可可椰子果實蒂腐病之研究

Abstract

可可椰子(Cocos nucifera L.)為熱帶地區重要經濟作物，然而採收後鮮果實的儲藏問題，一直以來皆困擾著相關行業從事者。作者於2005年間，發現採自屏東縣九如、長治、內埔等地之椰子果實，在採收數日後，開始自果頂或果實傷口出現果肉黑化、軟化之病徵，以及帶有特殊香味之病兆。自罹病果實內部可分離出一種於PDA平板培養基上菌落初期白色、一至二天後變黑，且散發強烈水果香氣之有隔真菌。該菌可產生兩種無性孢子，一種為自長形壺狀產孢梗開口冒出成長串之分生孢子，分生孢子短筒至長筒形、無色，成熟後為卵形，且略為厚壁，顏色轉為黑色，大小為8.5-16.0 × 4.7-6.7μm，其產胞梗大小為80.0-155.0 × 5.0-7.8μm；另一種為菌絲末端特化形成之卵形、黑色，排列成短鏈狀之厚膜孢子，大小為13.4-25.0 × 8.9-12.5μm。以分離所得菌株配對進行對峙培養，在兩個月後發現其中一組菌株配對產生淡咖啡色、球狀子囊殼，大小約280μm，有長約1100μm之黑色長喙；此子囊殼產生之子囊孢子為梭形，部分彎向一側，大小約12 × 3μm。依上述之形態特性，將此菌鑑定為Ceratocystis paradoxa (Dade) C. Moreau（無性世代：Thielaviopsis paradoxa (de Seynes) Höhn）。將此分離菌株接種於椰子果實上，可產生與最初發現相同之病徵，並且可再分離得到相同之菌株。此病原菌菌絲最適生長溫度為25-30℃，此時生長速度可達3.3cm/day，低於10℃或高於35℃時則幾乎不生長。在已知文獻中，此病原菌可在椰子樹上造成樹幹流膠病(stem bleeding)與心芽腐敗病(bud rot)，另在1955年巴西曾有果實蒂腐病(fruit basal rot)之報導，且病源同為C. paradoxa，但建議本病害亦可稱為黑腐病(black rot)。在病害調查上，發現此病害週年均可發生，但採收後開始發病之日數，則依時序而異，尤其在6~10月間，採收後10天內之發病率可上升至2%。而在寄主範圍上，本菌株可在鳳梨果實上造成鳳梨黑腐病（病原菌亦為C. paradoxa）之病徵，故此二病害之病原應屬相同。

Coconut (Cocos nucifera L.) is an important economic crop in tropical areas. Just like other fruits, the post-harvest diseases are big problems for farmers. Since 2005, coconut fruits harvested from Jiouru, Changjr, Neipu in Pintung county have showed a fruit rot disease. Principal symptoms are blackening of exocarp, mesocarp and then endocarp of coconut fruit. The affected fruit usually emitted fruit-type fragrant. A fungus was consistently isolated from the diseased fruits. Its colony on PDA plate was white in early stage but became black one or two days later. It emitred a strong fruity fragrance. This fungus produced two asexual spores. The first was phialospore-type conidia released in long chains from tip of long phialides. They were hyaline to mid-brown, cylindral to somewhat oval and thick-walled when mature, 8.5-16.0 × 4.7-6.7μm. The phialide had the size of 80.0-155.0 × 5.0-7.8μm. The second was chlamydospore formed in short chains from specialized hyphal tip, oval, black, 13.4-25.0 × 8.9-12.5μm. Dual cultures of all paired isolates on PDA with one piece of coconut exocarp induced the production of perithecia. Perithecia were brown, globose, 280μm in diameter, with a 1100μm long neck. Ascospores were ellipsoid, but some were unequally bent, 12 × 3 μm. According these characteristics, this fungus was identified as Ceratocystis paradoxa (Dade) C. Moreau (Anamorph：Thielaviopsis paradoxa (de Seynes) Höhn). Inoculation of all wild-type isolates on healthy coconut fruits reproduced the same black rot disease. The same pathogen was reisolated from the inoculated fruits. The temperature for hyphae growth of this fungus was 25-30℃, with the growth rate of 3.3cm/day. It cannot grow at temperatures lower than 10℃ or higher than 35℃. This pathogen was reported to cause stem bleeding disease in 2004 and bud rot disease of coconut in 1993, but a disease called fruit basal rot of coconut have been reported in 1955 in Brazil. With the same pathogen, we suggest this newly found disease can be also named as black rot. This disease accused on coconut fruits around all seasons, but is more serius in warm seasons, especially in the period from June to October. Disease incidence could reach 2% after 10 days of fruit storage. This black rot pathogen caused black rot disease of pineapple, while the pathogen from black rot of pineapple also caused black rot of coconut fruit, indicating that both diseases have the identical pathogen.