臺灣紅龍果莖部潰瘍病之研究

Abstract

紅龍果為仙人掌科(Cactaceae)，三角柱屬(Hylocereus)之多年生攀緣性多肉植物，病蟲害問題較少於其他作物，為臺灣新興果樹之一。近幾年來於臺灣各地之紅龍果果園常發現紅龍果莖部表面有黃點、紅點及潰瘍病徵，連果實表皮上也發現遭受黃點危害，造成賣相不佳，甚至果實腐爛。故本研究從2011年夏天開始至宜蘭、花蓮、彰化、南投及麥寮之紅龍果果園進行病害調查，採樣及病原分離、鑑定等工作，經病原分離所得到之分離株皆以菌落型態呈黑色之菌株佔最大比例，但分離率約僅為50%。經三種病原性測試，包括針刺接種、金鋼砂接種及孢子懸浮液噴灑接種，發現皆可於紅龍果莖部表面產生與田間所見相同之病徵，並且可再分離得到相同之病菌，故確定此一黑色菌株為造成紅龍果莖部黃點、紅點及潰瘍病徵之病原菌。因本病最近已被發表報告並命名為莖部潰瘍病，故本研究採用此一名稱，稱之為紅龍果莖部潰瘍病。本病病原黑色菌株於PDA平板培養基上菌落初期白色，待長滿培養皿後，從菌落中央開始往外變黑，即見產生節生孢子。其節生孢子為圓柱形、鈍橢圓形到甕形，深褐色，厚壁，0至2個隔膜，於病原菌接種之枝條上可發現產生柄子殼及分生孢子，分生孢子為橢圓形至卵形，端點圓形，0-1個隔膜。依上述型態鑑定及ITS分子鑑定結果，可將本病菌鑑定為Neoscytalidium dimidiatum。此病原菌菌絲最適生長溫度為30-35℃，於15℃生長緩慢，於40℃之環境下仍可生長，對照病原性測試結果可得知溫度較高時有利於發病。在藥劑防治測試方面，發現以24.9%待克利乳劑(EC)及23%菲克利水懸劑(SC)對菌絲生長抑制效果最佳。本研究於田間調查、病原性測試之結果上皆證明本病原可產生局部莖腐，但目前尚無法排除其他微生物複合感染或二次感染之可能性，故仍需後續研究探討Neoscytalidium dimidiatum與局部莖腐之間的關係。

Pitaya, belongs to the genus Hylocereus and the family Cacteceae, is a perennial succulent plant with less pest problems than other crops, it is now an important fruit crop in Taiwan. In recent years we found a new pitaya stem disease with symptoms of yellow spots, red spots and cankers on the stems in many Taiwan areas. Even the pitaya fruits are also affected, causing fruit rot and yield or quality losses. Therefore, we initiated the study on this disease and started to visit Yilan, Hualien, Changhua, Nantou, and Mailiao counties to conduct the field investigation since summer, 2011. The diseased spots and canker were isolated to cultivate the pathogen. Isolation results show that a black colony isolate can be isolated from all diseased canker or yellow spots with dominant proportion although the isolation rate is only about 50%. Three pathogenicity test methods thereafter were applied to prove the cause-effect relationship, including the needle inoculation, carborundum-scrubbing and spore suspension spraying methods. All inoculated pitaya stem can produce the identical canker with or without yellow spot symptoms. The same pathogen can be reisolated from all the inoculated stems in all three methods, determining that the black isolates is the pathogen that cause the pitaya stem canker showing yellow spots, red spots, canker and even stem rot symptoms. As the disease was recently reported and named as pitaya stem canker, we adopted this as the disease name. The colony of black isolates on PDA plate is white in early stage then became black from colony center as its arthroconidia produced in arthric chain on aerial hyphae. Its arthroconidia are dark brown, thick-walled, 0-2 septate with shapes of cylindrical, truncate, oblong-obtuse to doliiform. The inoculated pitaya stem could found to produce pycnidia and conidia on infected lesion. The conidia have 0-1 septate, ellipsoidal to oval, with round apex. According to the morphology and the ITS molecular identification results, the black isolates were identified as Neoscytalidium dimidiatum. The optimal temperature for hyphae growth of this fungus was 30-35℃. It grew slowly at 15℃ and could grow even at 40℃. Therefore, higher temperature is in favor of the disease development. Results of chemical control tests, showing that 24.9% difenoconazole emulsifiable concentrate (EC) and 23% hexaconazole suspension concentrate (SC) were able to completely inhibit the mycelia growth of this pathogen. From the field investigation and pathogenicity test, we can prove that the stem rot can be caused by this pathogen. However, we could not exclude the possibility of complex infection or secondary infection with other microorganism. Therefore, further studies are required to investigate the relationship between Neoscytalidium dimidiatum and the stem rot problem.