Kubaa R Abou, Djelouah K, D'Onghia A M, Addante R, Jamal M
Centre International de Hautes Etudes Agronomiques Méditerranéennes, Mediterranean Agronomic Institute (CIHEAM/MAIB), Via Ceglie 23, 70010 Valenzano, Bari, Italy.
Dipartimento di Biologia e Chimica Agro-forestale e Ambientale, University of Bari, Italy.
Plant Dis. 2008 Oct;92(10):1468. doi: 10.1094/PDIS-92-10-1468C.
During the spring of 2006, the main Syrian citrus-growing areas of Lattakia (Jableh, Aledyye, Eseelya, Siano, and Hresoon provinces) and Tartous (Almintar, Aljammase, Karto, Majdaloonelbahr, Yahmour, Amreet, Althawra, and Safita provinces) were surveyed to assess the presence of Citrus tristeza virus (CTV). Eight nurseries (approximately 130 plants per nursery), two budwood source fields (approximately 230 trees per field), and 19 groves (approximately 60 trees per grove) containing the main citrus varieties were visually inspected and sampled for serological assays. The hierarchical sampling method was carried out in each selected grove (2). Infected samples were collected from two nurseries, two budwood source fields, and six groves. Stems and leaf petioles from nursery trees and flower explants from the groves were collected and analyzed for CTV by direct tissue blot immunoassay (DTBIA) with the commercial kit from Plantprint (Valencia, Spain). Of 2,653 samples tested, 89 (4%) CTV-infected plants were detected. Five citrus varieties were found to be infected and Meyer lemon (Citrus limon 'Meyer') had the highest incidence at 16%. Numerous sweet orange varieties (Citrus sinensis L.) were found to be highly infected in the field, but only the Washington navel sweet orange was found to be infected in the nurseries. No clear CTV symptoms were observed during the survey. Samples that were positive for CTV by DTBIA were also positive by biological indexing on Mexican lime (C. aurantifolia) and immunocapture-reverse transcription-PCR as described by Nolasco et al. (3). Coat protein gene sequences obtained from five selected clones of a Syrian CTV isolate (GenBank Accession No. EU626555) showed more than 99 and 98% nucleotide sequence identity to a Jordanian CTV isolate (GenBank Accession No. AY550252) and the VT isolate (GenBank Accession No. U56902), respectively. Almost all infected samples induced moderate vein clearing symptoms when grafted to Mexican lime. Symptoms of vein clearing, leaf cupping, stunting, and stem pitting on Mexican lime were induced by graft transmission of CTV from one Valencia sample from the Tartous area. The viral inoculum is widely and randomly distributed in commercial groves, especially in the southern Tartous area and in some nurseries. To our knowledge, this is the first report of CTV in Syria. However, CTV was reported from the neighboring citrus-growing countries of Lebanon, Turkey, and Jordan (1), and the severe seedling yellows strain is present in this area, which poses a potential threat to Syrian citriculture. References: (1) G. H. Anfoka et al. Phytopathol. Mediterr. 44:17, 2005. (2) G. Hughes and T. R. Gottwald, Phytopathology 88:715, 1998. (3) G. Nolasco et al. Eur. J. Plant Pathol. 108:293, 2002.
2006年春季，对叙利亚主要的柑橘种植区拉塔基亚（贾卜莱、阿莱迪耶、埃斯埃利亚、西亚诺和赫鲁苏恩省）和塔尔图斯（阿尔明塔尔、贾马塞、卡尔托、马杰达隆埃尔巴赫、亚穆尔、阿姆里特、阿尔索尔拉和萨菲塔省）进行了调查，以评估柑橘衰退病毒（CTV）的存在情况。对8个苗圃（每个苗圃约130株植物）、2个采穗圃（每个采穗圃约230棵树）以及19个果园（每个果园约60棵树）进行了实地检查，这些地方种植有主要的柑橘品种，并采集样本进行血清学检测。在每个选定的果园中采用分层抽样方法（2）。从2个苗圃、2个采穗圃和6个果园采集到了受感染样本。采集了苗圃树木的茎和叶柄以及果园的花外植体，使用西班牙巴伦西亚Plantprint公司的商用试剂盒，通过直接组织印迹免疫分析（DTBIA）对CTV进行分析。在检测的2653个样本中，检测到89个（4%）受CTV感染的植株。发现5个柑橘品种受到感染，其中北京柠檬（Citrus limon 'Meyer'）的感染率最高，为16%。在田间发现许多甜橙品种（Citrus sinensis L.）受到高度感染，但在苗圃中仅发现华盛顿脐橙受到感染。在调查期间未观察到明显的CTV症状。通过DTBIA检测呈CTV阳性的样本，经墨西哥来檬（C. aurantifolia）生物学鉴定以及如诺拉斯科等人（3）所述的免疫捕捉逆转录聚合酶链式反应检测也呈阳性。从一株叙利亚CTV分离株的5个选定克隆中获得的外壳蛋白基因序列（GenBank登录号EU626555），与一株约旦CTV分离株（GenBank登录号AY550252）和VT分离株（GenBank登录号U56902）的核苷酸序列同一性分别超过99%和98%。几乎所有受感染样本嫁接至墨西哥来檬时都会引发中度的叶脉黄化症状。从塔尔图斯地区的一个巴伦西亚样本中通过CTV嫁接传播，在墨西哥来檬上引发了叶脉黄化、叶片卷曲、植株矮化和茎部凹陷症状。病毒接种体在商业果园中广泛且随机分布，尤其是在塔尔图斯南部地区和一些苗圃中。据我们所知，这是叙利亚关于CTV的首次报道。然而，在邻国黎巴嫩、土耳其和约旦的柑橘种植区已报道过CTV（1），并且该地区存在严重的幼苗黄化株系，这对叙利亚的柑橘种植业构成了潜在威胁。参考文献：（1）G. H. Anfoka等人，《植物病理学报（地中海地区）》44:17，2005年。（2）G. 休斯和T. R. 戈特瓦尔德，《植物病理学》88:715，1998年。（3）G. 诺拉斯科等人，《欧洲植物病理学报》108:293，2002年。
