由Botryosphaeria rhodina引起的番石榴莖潰瘍病及其病原性測定

Abstract

西元2003至2005年調查發現，番石榴莖潰瘍病普遍發生於高雄縣燕巢鄉、大社鄉、岡山鎮，台南縣後壁鄉、玉井鄉，及彰化縣溪州鄉、社頭鄉等番石榴主要產區。本病害造成主幹及分枝形成線形潰瘍且樹皮開裂，受害部位橫切面可見形成層及木質部組織褐化，並延伸至髓部(pith)組織；另外莖潰瘍病亦造成枝條萎凋，及主幹與分枝的樹皮條狀剝離，導致植株生長勢衰弱，且葉片佔萎而逐漸死亡。以菌絲塊人工傷口接種番石榴珍珠拔品種的植株後獲得相同的病徵。於高雄地區罹病植株的褐化組織及子囊抱子，分離獲得10個分離株進行形態觀察，依子囊孢子分離株鑑定病原菌的有性世代為Botryosphaeria rhodina;於田間潰瘍組織及BR-10分離株中可發現精子器(spermogonia)形成，扁球形至圓錐形；精子(spermatia)為無色，短桿狀；將10個分離株分別接種於含番石榴葉的15%水瓊脂(water agar)，並鍛於近紫外燈下培養，10個分離株皆產生Lasiodiplodia theobromae的分生孢子。選擇致病性(virulence)較強的BR-01與BR-11為供試菌株，接種於17種番石榴品種、草莓番石榴、真珠拔、模里西斯番石榴及7種熱帶果樹（包含鳳梨釋迦、印度棗、荔枝、六團邊、芒果、木瓜及蓮霧）的新梢，結果顯示模里西斯番石榴、荔枝、龍眼、芒果及鳳梨釋迦等對病原菌具有抗性。然而，番石榴新梢亦對2個芒果分離株及1個印度棗分離株具有抗性，顯示B. rhodina存在不同的病原型(pathotype)。此外，L. theobromae於枯萎靠接苗的接合部位(graft union)、乾枯的果柄及乾枯的新梢等部位的高分離率，顯示此些部位可能為田間的侵人感染點(infection site)。 The fungal pathogen Botryosphaeria rhodina has been identified as the causal agent of a guava (Psidium guajava L.) stem canker in Taiwan. According to a 3-year survey during 2003 to 2005, the stem canker was commonly found in guava orchards of Kaohsiung, Tainan, and Changhua Counties. Symptoms of the stem canker including linear cankers with bark cracks on the trunks and branches of guava tree were found on diseased plants. A brown discoloration was showed in the infected areas of cambiums and xylem, extending to the pith tissues. The cankers on the branchlets and separation of the bark strips on the branches and trunks resulted in retarding guava’s growth, leaf wilting, and progressive death. The same disease symptoms were observed in a guava cultivar ‘Zhen-zhu Ba’¶ through artificial inoculation of wounded tissues with mycelial agar discs. The ten isolates derived from either infected tissues or ascospores collected from three different geographic locations in Kaohsiung were used for morphological studies. Sexual stages of pathogen isolated from infected tissues were identified as B. rhodina. Spermogonia (160-220 110-140 m), suboblate to conical in shape, with hyaline, rod-like spermatia (2.5-4 1-1.5 m) were observed in the BR-10 isolate and the infected canker tissue. All isolates produced asexual spores of Lasiodiplodia theobromae on water agar medium with a piece of guava leaf under near-UV light. Two isolates, BR-01 and BR-11, were used for inoculation tests on 17 guava cultivars, strawberry guava, Jhen-jhu Ba, Mauritius guava and 7 tropical fruits, including atemoya, Indian jujube, lychee, longan, mango, papaya and wax apple. The results indicated that Mauritius guava and 4 tropical fruits (lychee, longan, mango and atemoya) were resistant to the pathogen. However, guava was resistant to two isolates of mango and one of Indian jujube. It showed that different pathotypes presented in B. rhodina. In addition, the results that L. theobromae was readily isolated from graft unions of blighted seedlings, dry fruit stalks, and blighted shoots might imply the possible infection sites of pathogen.