Sinclair W A, Townsend A M, Griffiths H M, Whitlow T H
Department of Plant Pathology, Cornell University, Ithaca, NY 14853.
USDA-ARS, Floral and Nursery Plants Research Unit, United States National Arboretum, Glen Dale, MD 20769.
Plant Dis. 2000 Dec;84(12):1266-1270. doi: 10.1094/PDIS.2000.84.12.1266.
Elms (genus Ulmus) of six clonal cultivars representing Eurasian species and hybrids were grafted when 2 to 3 years old with bark patches from U. rubra infected with an elm yellows phytoplasma or were left untreated as controls. The cultivars were U. glabra × minor 'Pioneer', U. minor × parvifolia 'Frontier', U. parvifolia 'Pathfinder', U. wilsoniana 'Prospector', and the complex hybrids 'Homestead' and 'Patriot'. Trees were evaluated for infection and symptoms 1 or 2 years after inoculation. Infection was detected via the 4',6-diamidino-2-phenylindol e·2HCl (DAPI) fluorescence test in 26 of 86 grafted trees representing five cultivars. Infection of selected trees was confirmed by polymerase chain reaction (PCR) amplification of a fragment of phytoplasmal rDNA, and the phytoplasma was identified by restriction fragment length polymorphism (RFLP) analysis of the amplified DNA using restriction enzymes AluI, RsaI, and TaqI. Elm yellows phytoplasma was also identified by nested PCR and RFLP analysis in two of seven inoculated, healthy-appearing, DAPI-negative trees and one noninoculated control tree. All RFLP profiles were identical to that of reference strain EY1. Phytoplasma-associated symptoms, observed in five cultivars, included suppressed growth, progressive size reduction of apical shoots and leaves, chlorosis, foliar reddening, witches'-brooms, and dieback. Phyto-plasma was not detected in cv. Homestead. Possible resistance of this cultivar to elm yellows phytoplasma was indicated by localized phloem necrosis in stems below inoculum patches.
选取了代表欧亚物种和杂种的六个克隆品种的榆树（榆属），在其2至3岁时，用感染了榆树黄化植原体的红榆树皮贴片进行嫁接，或作为对照不做处理。这些品种包括光叶榆×小叶榆‘先锋’、小叶榆×朴树‘前沿’、朴树‘探路者’、天目榆‘勘探者’，以及复合杂种‘家园’和‘爱国者’。接种1或2年后，对树木的感染情况和症状进行评估。通过4',6-二脒基-2-苯基吲哚二盐酸盐（DAPI）荧光测试，在代表五个品种的86株嫁接树中的26株检测到感染。通过对植原体rDNA片段进行聚合酶链反应（PCR）扩增，确认了部分树木的感染情况，并使用限制性内切酶AluI、RsaI和TaqI对扩增的DNA进行限制性片段长度多态性（RFLP）分析，鉴定了植原体。在七株接种后外观健康、DAPI检测为阴性的树木中的两株，以及一株未接种的对照树中，通过巢式PCR和RFLP分析也鉴定出了榆树黄化植原体。所有RFLP图谱均与参考菌株EY1相同。在五个品种中观察到的与植原体相关的症状包括生长受抑制、顶梢和叶片逐渐变小、黄化、叶片变红、扫帚状丛生枝和枯死。在‘家园’品种中未检测到植原体。接种部位下方茎干中的局部韧皮部坏死表明该品种可能对榆树黄化植原体具有抗性。
