Fruit rot of oriental pear caused by Erwinia carotovora subsp. carotovora and in vitro bactericide screening

於1998 年6 月間在南投縣中寮鄉種植之橫山梨發現果實腐爛問題，經柯霍氏 法則確認該病原為細菌，隔年（1999）於新竹栽培之橫山梨亦發現相同病害。此 病害主要危害果實，在枝條及葉片上不引起病徵，果實初期病徵僅在表皮上出現 淡褐色水浸狀小斑點，病斑繼續擴展造成內部果肉腐爛，輕壓表皮具彈性，嚴重 時整個果實腐爛，並有乳白色汁液與氣泡湧出。從罹病果實上分離之細菌，經生 理生化測定，Biolog 鑑定系統，專一性引子對PCR 分析等方法，鑑定該病原細菌 為Erwinia carotovora subsp. carotovora。將此病定名為果腐病。以蟲針沾細菌懸浮 液刺傷果實及浸菌無傷口接種等方法接種橫山梨果實，發現僅傷口處理者出現病 徵，且病徵擴展迅速，病斑直徑可達1.2 cm/day，該病菌也感染新興梨，在馬鈴薯、 胡蘿蔔及洋蔥等組織上具有致腐能力，且可造成煙草植株腐爛。果實蠅媒介試驗 顯示在有果實蠅成蟲之蟲箱內，不論以病菌處理果實蠅取食之洋菜膠或以病菌直 接覆於果實上，供試之橫山梨及新興梨果實均出現典型果腐病徵。另外，讓果實 蠅於梨果實上產卵後，於產卵孔滴病原菌也產生相同果腐病徵。測試市售11 種藥 劑在一般使用濃度下對該病菌生長之抑制效果，結果顯示除鋅乃浦外，其餘供試 之枯萎寧、四環黴素、鏈黴素、安達菌、嘉賜黴素、嘉賜銅、氫氧化銅、鹼性氯 氧化銅、銅合浦及鋅錳乃浦等藥劑於培養基上均能抑制該病菌之生長。 An incidental fruit rot of oriental pears occurred in Chung Liao, Nantou in July, 1998. The causal agent attacked fruits and caused severe fruit rot. After being attacked, fruits firstly showed water-soaked lesions, the tissues became extremely soft, followed by a slimy decay that associated with mushy slimy white color ooze emerging from lesions. An unknown bacterium was isolated from the diseased fruits and followed identification based on physiological characteristcs, Biolog analyses and primer pairs specific to Erwinia carotovora and Erwinia chrysanthemi using polymerase chain reaction, the causal agent was therefore identified as Erwinia carotovora subsp. carotovora (Ecc). Inoculation tests conducted in the laboratory indicated that the expansion of the soft lesion could reach up to 1.2 cm diameter per day. In addition to pear, the bacterium could also cause soft rot of potato, carrot, onion and tobacco. Transmission tests combining oriental fruit flies and Ecc in a confined space indicated that oriental fruit flies could transmit the disease through feeding or egg laying. Screening eleven chemicals include Streptomycin + Tetracycline, Tetacycline, Streptomycin, Thiophanate methy1 + Streptomycin, Kasugamycin, Kasugamyucin + Copper oxychloride, Copper hydroxide, Copper oxychloride, Copper oxychloride + Mancozeb, and Mancozeb in vitro, the results showed that all chemicals, except Zineb, effectively inhibited bacterial growth at various dosage tested