澳洲石斛疫病病原菌的鉴定及其杀菌剂毒力测定

Pathogen Identification and Fungicide Toxicity Test of Phytophthora Blight in Dendrobium kingianum

澳洲石斛(Dendrobium kingianum)属于兰科石斛属植物,在我国作为观赏植物被广泛种植。近年来,广东省澳洲石斛生产上发生一种疫病,该病害为害茎杆和叶片,引起受害部位变褐腐烂,植株死亡,对生产造成严重的影响。从发病的澳洲石斛上分离获得一种真菌,通过致病性测定显示,该菌可以侵染健康的澳洲石斛盆栽植株引起发病,表现出的症状与大田症状相似。从接种发病的植株上再次分离得到的菌株与接种菌的形态特征一致,说明原分离菌为引起澳洲石斛疫病的病原菌。通过形态学特征观察和β-微管蛋白基因(β-tubulin,tub)序列分析对分离菌株进行了鉴定。该菌株的形态学特征与棕榈疫霉(Phytophthora palmivora)基本一致。BLAST比对分析发现,本研究中的2个菌株(SHL918和SHL921)的tub基因序列与棕榈疫霉的相似性均为99%。在基于tub基因构建的系统发育树上,研究菌株与棕榈疫霉聚在同一分支上,支持率为100%。因此,结合形态学特征和系统发育分析将引起澳洲石斛疫病的病原菌鉴定为棕榈疫霉(P.palmivora)。棕榈疫霉侵染澳洲石斛引起疫病为首次报道。进一步采用菌丝生长速率法测定10种杀菌剂对澳洲石斛疫病病原菌的毒力作用,结果显示,双炔酰菌胺、烯酰吗啉、甲霜灵和精甲霜灵·代森锰锌4种杀菌剂对该病原菌的毒力较强,EC50分别为0.00003、0.0628、0.2381、0.5457μg/mL;其次是百菌清、嘧菌酯和代森锰锌,EC50均小于10μg/mL;而霜霉威盐酸盐和三乙膦酸铝的抑制效果差,EC50均大于100μg/mL;多菌灵对该病原菌基本无抑制作用,EC50大于1000μg/mL。本研究结果可为澳洲石斛疫病的田间防治提供理论依据。

Dendrobium kingianum belongs to Orchidaceae family,which is widely grown as an ornamental plant in China.In recent years,a blight disease in D.kingianum is observed in Guangdong province,China.This disease infects the stems and leaves of D.kingianum,causing brown rot and plant death.It has a serious impact on production.A fungus was isolated from the diseased plants of D.kingianum.The pathogenicity test showed that this fungus could infect healthy potted plants and cause the disease.The symptoms on inoculated plants were similar to field symptoms.Morphological characteristics of the fungus from the inoculated plants were consistent with that of the original fungus from field samples.The pathogen was identified by both morphological characteristics andβ-tubulin(tub)gene sequence analysis.The morphological characteristics of the isolates were similar to Phytophthora palmivora.BLAST results showed both the sequences of two isolates in this study were 99%identical to the sequence of P.palmivora.In the maximum likelihood(ML)tree based on tub gene sequences,the strains in this study clustered with P.palmivora with 100%support.Therefore,P.palmivora was identified as the pathogen of Phytophthora blight on D.kingianum based on morphological characteristics and phylogenetic analysis.This is the first report of P.palmivora causing Phytophthora blight on D.kingianum in China and worldwide.The inhibitory effect of 10 fungicides on P.palmivora was determined using the mycelial growth rate method.The results showed that four fungicides,namely diacetylomyamide,dimethomorph,metalazepine and metalazepine·mancozeb,were the top four toxic to P.palmivora,and the EC50 value was 0.00003μg/mL,0.0628μg/mL,0.2381μg/mL and 0.5457μg/mL,respectively.It was followed by chlorothalonil,pyrimethole and mancozeb,the EC50 was less than 10μg/mL.However,the effect of downy mildew hydrochloride and triethylphosphonate was poor,and the EC50 was more than 100μg/mL.Carbendazim showed no inhibitory effect,the EC50 was more than 1000μg/mL.The result would provide a theoretical basis for the prevention and control of Phytophthora blight in Dendrobium.