Abou-Jawdah Yusuf, Karakashian Armig, Sobh Hana, Martini Marta, Lee Ing-Ming
Faculty of Agricultural and Food Sciences, American University of Beirut, P.O. Box 11-0236, Beirut, Lebanon.
Molecular Plant Pathology Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705.
Plant Dis. 2002 May;86(5):477-484. doi: 10.1094/PDIS.2002.86.5.477.
An epidemic of almond witches'-broom has devastated almond production in Lebanon. Thousands of almond trees have died over the past 10 years due to the rapid spread of the disease. The symptoms, which include early flowering, stunted growth, leaf rosetting, dieback, off-season growth, proliferation of slender shoots, and witches'-brooms arising mainly from the main trunk and roots, resemble those caused by phytoplasmal infections. For the detection of the putative causal agent, nested polymerase chain reaction (PCR) was performed using universal primers (P1/P7, R16mF2/R16mR1, and R16F2n/R16R2) commonly used for the specific diagnosis of plant pathogenic phytoplasmas. Phytoplasmas were readily detected from infected trees with witches'-broom symptoms collected from three major almond growing regions in Lebanon. Restriction fragment length polymorphism (RFLP) analysis of PCR products amplified by the primer pair R16F2n/R16R2 revealed that the phytoplasma associated with infected almonds is similar to, but distinct from, members of the pigeon pea witches'-broom phytoplasma group (16SrIX). A new subgroup, 16SrIX-B, was designated. Sequencing of the amplified products of the phytoplasma 16S rRNA gene indicated that almond witches'-broom (AlmWB) phytoplasma is most closely related to members of the pigeon pea witches'-broom phytoplasma group (with sequence homology ranging from 98.4 to 99.0%). Phylogenetic analysis of 16S rDNA sequences from AlmWB phytoplasma and from representative phytoplasmas from GenBank showed that the AlmWB phytoplasma represents a distinct lineage within the pigeon pea witches'-broom subclade. The same phytoplasma appears also to infect peach and nectarine seedlings.
扁桃树扫帚病疫情已使黎巴嫩的扁桃生产遭受重创。在过去10年里，由于该病的迅速传播，数千棵扁桃树死亡。其症状包括早花、生长受阻、叶片丛生、枝梢枯死、非季节性生长、细枝增生以及主要从主干和根部生出的扫帚状丛生枝，这些症状与植原体感染所引起的症状相似。为检测假定的致病因子，使用了通常用于植物病原植原体特异性诊断的通用引物（P1/P7、R16mF2/R16mR1和R16F2n/R16R2）进行巢式聚合酶链反应（PCR）。从黎巴嫩三个主要扁桃种植区采集的有扫帚病症状的感染树中很容易检测到植原体。对引物对R16F2n/R16R2扩增的PCR产物进行限制性片段长度多态性（RFLP）分析表明，与感染扁桃相关的植原体与木豆扫帚病植原体组（16SrIX）的成员相似，但又有所不同。于是指定了一个新的亚组，即16SrIX - B。对植原体16S rRNA基因扩增产物进行测序表明，扁桃树扫帚病（AlmWB）植原体与木豆扫帚病植原体组的成员关系最为密切（序列同源性为98.4%至99.0%）。对AlmWB植原体和来自GenBank的代表性植原体的16S rDNA序列进行系统发育分析表明，AlmWB植原体在木豆扫帚病亚分支内代表一个独特的谱系。同样的植原体似乎也感染桃和油桃幼苗。
