腐霉菌引起薰衣草根腐病之研究

Abstract

薰衣草具有觀賞、烹飪及醫療等廣泛用途，為目前台灣香草業中重要的經濟作物之一，唯自國外引進後發現，其在田間極易發生根腐病害，罹患根腐病之薰衣草根部褐變、腐敗，嚴重者地上部萎凋甚至全株枯死。自2011年起至台灣中北部三個薰衣草栽培區皆可調查發現根腐病病株，並從罹病株分離得到根腐病菌，包括Pythium irregulare 、 Pythium “group F”、 Pythium spinosum 、 Pythium myriotylum 及Phytophthora nicotianae等五種，其中以Pythium在田間檢出率達59％為最主要。將上述五種根腐病菌以游走孢子懸浮液或菌絲塊接種至齒葉薰衣草、羽葉薰衣草、甜薰衣草及甜馬郁蘭四種香草之扦插苗，於試管中進行病原性檢測，發現皆可造成根部變色、腐敗，與田間所觀察到之病徵相同，對照組則未發病。自接種發病之病根上亦可再分離得到原接種之菌株，已符合柯霍氏法則，證實上述五種根腐病菌皆可造成上述四種香草之根腐病。其中又以Pythium spinosum 、 Pythium myriotylum及Phytophthora nicotianae等三種對香草扦插苗致病力較強，故能造成地上部萎凋病徵，且嚴重者可致死，故此三者可能是造成田間薰衣草萎凋之主要病原，而Pythium irregulare 及Pythium “group F”田間分離率雖高，但皆無法造成萎凋也不能致死，屬病原性較弱者，僅造成根腐之潛隱性病徵(subclinical symptoms)。另外亦發現，齒葉薰衣草為四種香草中最感病者，甜薰衣草次之，羽葉薰衣草則為較具抗性者，甜馬郁蘭則僅對P. myriotylum較感病。

Lavender as an ornamental, culinary and medicinal herb, now is one of the economically important crop in agricultural industry in Taiwan. Since lavender introduced from abroad, it was found to be frequently affected with root rot diseases. The diseased plants showed symptoms of root browing and root rot . The severely infected plants wilted, and died in the long run. In this study, the root rot diseases of lavender plants can be found in all three lavender plantation areas in northern and central parts of Taiwan in 2011. Five root rot isolates, including Pythium irregulare, Pythium “group F”, Pythium spinosum, Pythium myriotylum and Phytophthora nicotianae were isolated from these diseased roots of lavender and sweet marjoram. Results also showed that Pythium spp. are dorminant pathogens as 59% of the diseased roots contained this species. Pathogenicity tests using zoospore suspensions or mycelial pellets to inoculate the healthy lavender cuttings in tubes showed that all five isolates can induce the root browing and root rot symptoms on all three lavender cultivars including dentata lavender, fernleaf lavender ,sweet lavender and sweet marjoram. No symptoms developed on control plants. Five root rot pathogens can be consistently reisolated from symptomatic roots after the pathogenicity tests . These results proved that all of five isolates are root rot pathogens of lavender or sweet marjoram according to the Koch’s postulates. Among these pathogens, three are stronger pathogens as they can cause wilt and death of the test cuttings. They are Pythium spinosum, Pythium myriotylum and Phytophthora nicotianae . On the other hand, Pythium irregulare and Pythium “group F” are weak pathogens to all the four different test cuttings. They can only produced subclinical root rot symptoms. This study also found that among these three lavender cultivars, dentata lavender was the most susceptible host to these root rot pathogens, while fernleaf lavender showed the higher resistence to them. Sweet marjoram was, however, only susceptible to Pythium myriotylum.