莴苣黄化病植原体的分子鉴定

为了明确新疆莴苣黄花病植原体的分类地位，采用巢式PCR和PCR技术对表现黄化症状的莴苣植株分别利用植原体16S rRNA基因和tuf基因通用引物P1／P7、R16F2n／R16R2和fTufu／rTufu进行扩增，得到大小约1．2kb和0．8kb的特异性片段，对所得片段克隆、测序和序列分析。结果表明：它们分别和榆树黄化组（Elm yellows group）成员的16S rRNA基因、tuf基因同源性最高，分别高于98．6％和92．4％。基于16S rRNA基因和tuf基因的系统进化树分析显示，其均与植原体16Sr V组成员位于同一分支上。对16S rRNA基因的iPhyClassifier分析结果表明，其与榆树黄化组B亚组（16Sr V—B）代表株系JWB（AY197661）具有相同的酶切图谱。所有结果表明莴苣黄化病植原体（LSY）属于榆树黄化组B亚组（16Sr V-B）。

Molecular Identification of Lactuca sativa Yellows Phytoplasma

In order to identify the taxonomic status of Lactuca sativa yellows phytoplasma, using phytoplasma universal primers P1/P7 ,R16F2n/R16R2 and fTufu/rTufu for 16S rRNA gene and tuf gene,DNA fragments about 1.2 kb and 0.8 kb in length were amplified by nested-PCR and PCR from the total DNA of Lactuca sativa exhibiting yellows naturally. When the fragments were cloned, sequenced and subjected to sequence analysis, the result showed that the 16S rRNA gene and tuf gene of phytoplas- ma isolate Lactuca sativa yellows （LSY） shared the highest similarity of 98.60% and 92.4%, respectively,comparing with Elm yellows group phytoplasma （16SrV）. In the phylogenetic trees constructed with 16S rRNA and tuf genes, LSY was clustered with phytoplasmas of 16SrV. The 16S rRNA gene of LSY had identical patterns with JWB （AY197661） using online analysis of iphyClassifier for 16S rDNA. All these results indicated that the phytoplsama associated with Lactuca sativa yellows belonged to the subgroup B of Elm yellows group （16SrV-B）.