台灣蔬菜細菌性軟腐病菌之物種多樣性

Species diversity of bacterial soft rot pathogens of vegetables

Pectobacterium及Dickeya屬之軟腐細菌是引起植物軟腐病的重要病原，可感染多種經濟作物，造成嚴重損失。軟腐細菌原分類於Erwinia屬，因分子系統分類學之進展，其分類地位已重新修訂，且持續有新物種被發現，因此有必要重新瞭解台灣的軟腐細菌。本研究根據16S rDNA gene、dnaX、leuS及recA等基因之序列，分析原Erwinia屬的9株蔬菜軟腐細菌及2株未知軟腐細菌之分類地位。結果顯示原E. carotovora subsp. carotovora菌株分別歸類於P. aroidearum、P. brasiliense、P. colocasium及Pectobacterium spp.，原E. chrysanthemi菌株則為D. fangzhongdai，而未知2株菌株分別為P. brasiliense 及P. versatile。除P. brasiliense菌株無法引起洋蔥組織軟腐之外，其餘供試菌株對馬鈴薯及洋蔥皆具有致腐能力，但菌株間有顯著差異。供試菌株皆可產生果膠分解酵素，但僅D. fangzhongdai菌株可產生藍色色素。供試菌株培養在pH5至pH10之液態營養培養基中皆可生長，但在pH4中不利生長，且菌株間有明顯差異。本研究顯示台灣蔬菜軟腐細菌存在物種多樣性，此結果將有助於瞭解台灣細菌性軟腐病之分類現況。

Soft rot bacteria of the genera Pectobacterium and Dickeya are important pathogens that cause the soft rot diseases in plants. They can infect a variety of economic crops and cause severe losses. Soft rot bacteria were originally classified to the genus Erwinia. With the progress of molecular taxonomy, their taxonomic status has been revised and new species continue to be discovered. Thus, it is necessary to understand the soft rot bacteria in Taiwan again. Based on 16S rDNA, dnaX, leuS and recA gene sequences, we analyzed the phylogenetic placement 9 strains of the original Erwinia genus and 2 unknown strains of soft rot bacteria of vegetables. Results showed that the original E. carotovora subsp. carotovora strains were classified as P. aroidearum, P. brasiliense, P. colocasium, and Pectobacterium spp. and the original E. chrysanthemi strain was identified as D. fangzhongdai. The unknown strains were P. brasiliense and P. versatile. Almost all tested strains were able to induce soft rot symptoms on potato and onion. Only strains belonging to P. brasiliense did not induce symptoms on onion. There were significant differences among the symptom severities caused by different strains. All tested strains can produce pectolytic enzymes, but only the D. fangzhongdai strain can produce blue pigment. Tested strains were able to grow in nutrient broth adjusted to pH5 to pH10, but not in those adjusted to pH4. There were significant different among the OD600 values of different strains. This study revealed the species diversity of soft rot bacteria causing vegetable diseases in Taiwan. The results will help to understand the current status of bacterial soft rot in Taiwan.