引起玫瑰根腐病發生之環境因子及其防治藥劑篩選

Environmental factors affecting disease development of rose root rot and the chemical screening for the disease control in Taiwan

玫瑰根腐病是由腐霉菌 （Phytopythium helicoides） 感染所造成，將此菌游走子懸浮液接種於盆栽玫瑰幼苗根部，在24-40℃環境中可造成供試植株出現根腐與萎凋病徵，最適發病溫度為28-36℃；接種後的盆栽玫瑰根部不浸水或浸水1天後則不會出現病徵；浸水2天或以上則會造成病害發生，浸水天數愈久則病害越嚴重。苗齡小於6個月的玫瑰苗接種才會發病，接種苗齡2、4及6個月的2品種盆栽玫瑰苗（萬年紅、埔里之星），其發病度指數分別為1.8-2.7、1.3-1.8及0；盆栽玫瑰接種試驗皆以埔里之星品種較感病。以含有0.1-1000mg/L不同供試藥劑的培養基測試對供試病原菌菌絲直線生長抑制率，結果顯示半抑制濃度（IC50） 小於20 mg/L者為氟比拔克、依得利及滅達樂，介於20-200 mg/L者為中和化亞磷酸及達滅芬。盆栽試驗結果顯示，中和化亞磷酸、亞磷酸二氫鉀、氟比拔克、滅達樂、依得利、達滅芬皆能降低供試植株的發病度，具有防治潛力。而田間試驗顯示氟比拔克、銅滅達樂、中和化亞磷酸與亞磷酸二氫鉀具有防治效果，以後二者效果較好，可使發病率由對照組的23.1%降至7.0%以下。

Root rot disease caused severe reduction of rose production, and Phytopythium helicoides is proved as the major causal agent. Zoospore suspension of the pathogen was used to infect roots and basal stems of potted rose seedlings, and the artificial inoculation test caused root rot and wilt symptoms of the tested plants at 24–40°C with the optimum temperature for disease development at 28–36℃. In the further inoculation test, potted rose seedlings showed no symptom if they were soaked in water for only 1 day or without water. Soaking for 2 days or more will cause disease development, and the longer the soaking days were, the more severe the disease symptoms showed. Furthermore, other test result showed that young seedlings were more susceptible to the pathogen. While 2, 4 or 6 months old of the potted rose seedlings (cultivars: Wannainhong and Puli Star) were inoculated with pathogen, the disease severity indexes were respectively 1.8–2.7, 1.3–1.8 and 0. In all the artificial inoculation test Puli star cultivar were more susceptible than Wannainhong cultivar. For chemical screening, the media containing 0.1-1000mg/L of different chemicals were used to test the inhibition of the linear mycelial growth of the pathogen. The tested chemicals which had the half maximal inhibitory concentration ( I C 5 0 ) less than 2 0 mg/ L were fluopicolide + propamocarb hydrocholoride, etridiazole, and metalyxyl-copper; which 20–200 mg/L were monopotassium phosphate and dimethomorph. In the potted experiments, those chemicals mentioned above could significantly reduce the disease severity of rose root rot, and showed high potential for disease management in the field. The results of field trials showed that fluopicolide + propamocarb hydrocholoride, metalyxyl-copper, monopotassium phosphate, and neutralized phosphorous acid could significantly reduce disease incidence of the field roses. The latter two chemicals had better effects, which could reduce the disease incidence from 23.1% to less than 7.0%.