由Phytopythium helicoides引起之玫瑰根腐病

Root rot of rose caused by Phytopythium helicoides in Taiwan

2015年在南投縣埔里鎮數處玫瑰栽培田及國姓鄉一處玫瑰育苗場發現一種玫瑰新病害，主要病徵為植株幼苗根腐與莖基部褐化腐敗，嚴重時會造成植株萎凋枯死。一種腐霉菌由罹病植株的根部與莖基部組織可持續的被分離得到，於26－35℃之溫室條件下，將該腐霉菌的游走子懸浮液接種到盆栽玫瑰幼苗根部，2週之後會出現與田間及育苗場罹病玫瑰苗相同的病徵，並能再分離得到與原接種的同種腐黴菌，完成科霍氏法則測試，證實其病原性，並將此病害定名為玫瑰根腐病。此病原菌經由形態特徵以及核醣體內轉錄區間（rDNA internal transcribed spacer）核酸序列之鄰近連接法（Neighbor-Joining）分析，鑑定為Phytopythium helicoides。此病原菌在瓊脂培養基上菌絲生長溫度範圍為12－40℃，最適生長溫度為28－36℃，經由人工接種証實本病原菌可感染數種供試作物幼苗，可在玫瑰、巴西野牡丹、藍星花、草莓及左手香造成嚴重根腐病徵，在青椒及萵苣造成輕微根腐，可以感染百香果、胡瓜及青蔥根部但不會造成病徵。

"In 2015, a new rose disease was discovered in several rose cultivation fields in Puli Township, Nantou County, and a rose nursery in Guoxing Township, Nantou County, Taiwan. The main symptoms are root rot and basal stem rot, which caused plants to wither and die. A Phytopythium species was constantly isolated from diseased root and basal stem tissues of the infected plants. Zoospore suspension of the Phytopythium species was used for pathogenicity test of potted rose seedlings under the greenhouse conditions of 2635℃. The inoculated plants showed similar symptoms mentioned above 7-10 days after inoculation, and the same Phytopythium species could be re-isolated to confirm the Koch's postulates. The pathogen was identified as Phytopythium helicoides based on morphology and phylogenetic analysis of the nucleic acid sequence of the rDNA internal transcribed spacer. Mycelium of P. helicoides could grow at 12-40℃, and the optimum growth temperature is 2836℃. In the host range test of potted plants, P. helicoides could infect and cause severe root rot in roses (Rosa hybrida Hort.), glory flower (Tibouchina semidecandra Cogn.), blue daze (Plumbago auriculata Lam.), strawberry (Fragaria ananassa Duch.) and Indian borage (Coleus amboinicus Lour.), but could only cause mild root rot in green peppers (Capsicum annuum L.) and lettuce (Lactuca sativa var. sativa L.). It could infect roots of passion fruit (Passiflora edulis Sims), cucumber (Cucumis sativus L.) and green onion (Allium fistulosum L.) without producing any symptom."