杭白菊叶枯病病原菌鉴定及其对多菌灵的抗性机制

Identification of the pathogen causing the leaf blight of Dendranthema morifolium and its resistance mechanism to carbendazim

为明确浙江省桐乡市发生的杭白菊叶枯病的病原菌,采用传统组织分离法对采集的病样进行病原菌分离,在测定其致病性的同时,结合形态学特征及基于核糖体内部转录间隔区(ITS)、nrDNA大亚基(LSU)和β-微管蛋白基因(TUB2)的联合系统发育分析对该病原菌进行鉴定,并测定其对多菌灵的抗性。结果表明,从杭白菊叶枯病病样中共分离到35株菌株,在回接试验中杭白菊表现出的症状与田间自然发病症状一致,证明分离到的菌株为引起杭白菊叶枯病的病原菌。该病原菌菌丝生长初期为淡黄色,后为灰白色;培养25 d后菌落上的黑色球形分生孢子器产生大量液体状的淡粉色分生孢子堆;分生孢子为单胞、无色、长椭圆形,大小(n=200)为2.8~4.9μm×1.2~3.0μm,初步判断该病原菌是茎点霉属Phoma真菌P. bellidis。基于ITS、LSU、TUB2联合系统发育分析的分子鉴定结果与形态学鉴定结果一致,确定引起该病害的病原菌为P. bellidis。该病原菌对多菌灵的抗性频率为94.3%,且全部为高水平抗性菌株,抗药性机制为其TUB2的E198A突变,即TUB2的第198位密码子从GAG突变为GCG,导致第198位氨基酸从谷氨酸(Glu)突变为丙氨酸(Ala)。

In order to clarify the causal agent of leaf blight of Dendranthema morifolium,from which diseased samples were collected in Tongxiang,Zhejiang Province,the pathogenic fungus was identified based on the pathogenicity tests of isolates,morphologic characteristics and multi-locus phylogenetic analysis combing ITS,LSU and TUB2,and the resistance of this pathogen to carbendazim was studied.The results showed that the 35 isolates from the diseased plants could cause similar symptoms as in fields when healthy leaves of D.morifolium were artificially inoculated.Colonies of the pathogen were initially yellowy,and later became grayish-white.After incubated for 25 d,black spherical pycnidia on plates produced many liquid,light pink conidium heaps.Conidia were single-celled,colorless,long oval,and 2.8-4.9μm×1.2-3.0μm in size(n=200).Morphological characteristics were consistent with multi-locus phylogenetic proofs,indicating that leaf blight disease of D.morifolium was caused by Phoma bellidis.Further studies indicated that the resistance frequency of carbendazim was 94.3%in P.bellidis on D.morifolium from Tongxiang and all the resistant isolates belonged to high-level resistance.Sequence alignment indicated that the mechanism of carbendazim-resistance was the substitution of GCG for GAG at codon 198 ofβ-tubulin gene in high-level resistant isolates,which led to a substitution of glutamic acid for alanine at codon 198(E198 A).