薰衣草根腐疫病發病生態及非農藥防治之研究

Abstract

薰衣草(Lavandula spp.)屬唇形科(Lamiaceae)薰衣草屬(Lavandula)之植物，皆為芳香的常綠灌木或亞灌木，原產於地中海沿岸，性喜冷涼乾燥環境，主要分布在法國、西班牙及義大利。自從台灣由國外引入薰衣草栽培後，薰衣草常因台灣夏季高溫多雨而不利生長，一般多認為是因為夏季高溫及淹水此兩種環境因素使薰衣草栽培不易，以至於薰衣草無法順利度夏。但本研究及過往之報告已指出，薰衣草於入夏後易被Phytophthora nicotianae感染根部而造成根腐疫病，罹患根腐疫病的薰衣草，可發現根部有褐化現象，嚴重者地上部逐漸萎凋、葉子轉為灰綠色進而全株枯死。本研究亦探討栽培環境對薰衣草根腐病發病生態之影響，以及篩選出除了現行防治藥劑以外之非農藥防治資材。本研究所得之薰衣草根腐疫病分離株經柯霍氏法則測試其病原性，再以分子生物學鑑定後，確認Phytophthora nicotianae為薰衣草根腐疫病之病原菌。將此病原菌以不同溫度培養，發現菌絲可於16℃~37℃生長，最適生長溫度為22℃。以不同溫度處理觀察薰衣草根腐疫病病害發展中，發現病原菌可於溫度20℃侵染薰衣草，且隨溫度提升至35℃，疾病嚴重度也隨之提升；而當溫度提升至40℃，未接種病原菌之薰衣草在二週後仍保持健康，顯示薰衣草難以度夏之主因為根腐疫病等病害而非高溫本身。在土壤水潛勢對薰衣草根腐疫病病害之影響方面，以三種不同土壤水潛勢處理，薰衣草根腐疫病之發病率及疾病嚴重度皆無差異，而土壤水潛勢較低且未接種病原菌之薰衣草則會呈現輕微旱害病徵。在淹水環境對薰衣草根腐疫病病害發展之影響試驗，顯示淹水組薰衣草根腐疫病之發病率及疾病嚴重度在第三天時較不淹水者嚴重，但五天後二者已無差異。在非農藥防治資材之研究中，發現五種中草藥植物酒精萃取，都可以有效抑制病原菌遊走子發芽及菌絲生長，但實際應用於盆栽試驗時則未見顯著防治效果。在盆栽防治試驗方面，以丁香萃取液及五倍子萃取液防治效果較好，但其效果仍不及亞磷酸中和液及除疫寶。亞磷酸中和液不論在接種前或接種後處理都有良好的防治效果，其中以稀釋500倍於接種前7天施用之防治效果最佳，可使疾病嚴重度低於11%；接種後立即施用可使疾病嚴重度低於22%。除疫寶稀釋500倍於接種前7天施用可使疾病嚴重度低於6%。而就亞磷酸中和液及除疫寶兩者配置方式及保存方式比較，以除疫寶之配製方式最為簡便，且原液保存方式較不受環境影響而降解。在九種殺菌劑抑制菌絲生長之影響中，抑制效果最顯著之殺菌劑為滅達樂、達滅芬、嘉賜銅、福賽得及銅快得寧。建議選用滅達樂及達滅芬作為薰衣草根腐疫病菌之治療性殺菌劑，但滅達樂及達滅芬已有其他卵菌類病害之抗藥性紀錄，需輔以其他不同機制之卵菌殺菌劑使用。

Lavandula (common name lavender) is a flowering and aromatic shrub in the mint family, Lamiaceae. Lavender was derived from temperate area such as the Mediterranean countries, and mainly distributed over France, Spain and Italy. It prefers the dry and cool weather. Since lavender introduced from abroad, it was observed that the hot and humid environment in summer in Taiwan is not suitable for lavender to grow. It is thought that the hot and humid environment make lavender not easy to overcome the summer. This study and previous reports, however, show that lavender is frequently infected by Phytophthora nicotianae, and the root rot disease is the key problem in summer. This disease can cause the browning root rot , the discolored leaves and plant wilt. The severely infected plants will die. This study is also aimed to identify whether the environmental condition influence the occurrence of lavender root rot. Furthermore, several non-pesticide material, such as phosphorus acid and herbal plant extracts are also treated for their role in controlling the root rot disease. Through the pathogenicity test and molecular identification, we accomplish the Koch’s postulates of the disease caused by Phytophthora nicotianae. Culturing the pathogen at different temperature showed that the pathogen grows best at 22℃, although the myceliumcan grow at temperature range from 16℃ to 37℃. The study of lavender root rot disease at different temperature showed that the pathogen could infect the host lavender at 20℃ and the disease severity increased at high temperature of 35℃. The non-inoculated lavender still keep healthy at 40℃ for two weeks. It shows that the wilt and death of lavender in summer is caused by root rot disease rather than high temperature. The study of lavender root rot disease at different water potential showed that the three levels of water potential make no significant difference to disease incidence and severity, although the non-inoculated lavender appeared a slight drought injury in low water potential. The study of lavender root rot disease in flooding situation showed that the disease incidence and severity in flooding is less serious than non-flooding in three days, but it make no difference between both three days and five days. The non-pesticide control study showed that five plant extracts could inhibit the zoospore germination and mycelial growth significantly, but they didn’t have good effectiveness in the pot plant test. In the plot plant test, the neutralized phosphorous acid solution(NPA) and phosphoric acid had better effectiveness than the ethanol extract of clove and galla rhois. No matter pre-inoculated or post-inoculated, the sprayed NPA showed good effectiveness in reducing the disease. The NPA at 500X reduced the disease severity to 11% in pot plant test aftere pre-applied at seven days prior to inoculation, and reduced to 22% in pot plant test when applied after inoculation. The pre-application of phosphoric acid at 500X reduced the severity to 6% when applied before inoculation. Furthermore, the application of phosphoric acid is easier than NPA, and can not be affected by environment factors. Nine fungicides were treated for their inhibition effects on the pathogen. Among them, Metalaxyl, dimethomorph, kasugamycin＋copper oxychloride, fosetyl-aluminium and copper hydroxide + oxine-copper showed good inhibition in the mycelial growth test. The application of metalaxyl and dimethomorph recommended for controling the disease. However, it is reported that both has fungicide resistance problems. Therefore, they should be rotated with different fungicide of different mechanisms of action.