Francis M, Civerolo E L, Bruening G
University of California, Department of Plant Pathology, Davis 95616.
United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648.
Plant Dis. 2008 Jan;92(1):14-20. doi: 10.1094/PDIS-92-1-0014.
Readily transformable Nicotiana tabacum cv. SR1 (Petite Havana) was evaluated as a host for the bioassay of Xylella fastidiosa strains. Plant growing conditions and inoculation methods were optimized to enhance symptom expression 4 to 6 weeks post inoculation. Tobacco plants were inoculated with X. fastidiosa strains associated with almond leaf scorch disease (ALSD) and Pierce's disease (PD) of grapevine in California. All PD strains and the ALSD strain Dixon caused characteristic leaf scorch symptoms, whereas two other ALSD-associated strains (M12 and M23) caused severe leaf chlorosis followed by necrosis, leaf death, and drooping of older leaves. Symptoms began to develop 10 to 14 days post inoculation and proceeded to resemble those of X. fastidiosa-infected grape and almond. The presence of X. fastidiosa in affected plants was confirmed by reisolation of the pathogen, enzyme-linked immunosorbent assay, quantitative polymerase chain reaction (QPCR), and observation of X. fastidiosa cells by transmission and scanning electron microscopy, as well as by confocal laser scanning microscopy, in the xylem cells of inoculated plants. The pathogenicity of selected reisolated strains was confirmed by inoculation of grape plants in the greenhouse. The average levels of X. fastidiosa cells/g of tissue, estimated by QPCR, were higher for PD strains than for ALSD strains and reflected the relative titers of these strains in economic hosts. No symptoms were observed and bacteria were not detected in untreated tobacco or in tobacco inoculated with Xanthomonas campestris pv. campestris or water. Symptoms induced by Xylella fastidiosa in this bioassay were fully expressed within 2 months following inoculation. The described bioassay, under optimized environmental conditions, provides a useful system for studying X. fastidiosa strains (e.g., confirmation of pathogenicity and differentiation of PD and ALSD pathotypes) and for investigating X. fastidiosa-host interactions. N. tabacum cv. SR1 tobacco was a better bioassay host for X. fastidiosa than N. tabacum cvs. Havana, RP1, and TNN described previously.
对易于转化的烟草品种烟草（Nicotiana tabacum cv. SR1，小哈瓦那）进行了评估，以作为快速木杆菌（Xylella fastidiosa）菌株生物测定的宿主。优化了植物生长条件和接种方法，以增强接种后4至6周的症状表现。用与加利福尼亚州杏仁叶焦枯病（ALSD）和葡萄皮尔氏病（PD）相关的快速木杆菌菌株接种烟草植株。所有的PD菌株和ALSD菌株狄克逊（Dixon）都引起了典型的叶焦枯症状，而另外两个与ALSD相关的菌株（M12和M23）则引起严重的叶片黄化，随后坏死、叶片死亡以及老叶下垂。症状在接种后10至14天开始出现，并逐渐类似于被快速木杆菌感染的葡萄和杏仁的症状。通过病原菌的再分离、酶联免疫吸附测定、定量聚合酶链反应（QPCR）以及通过透射电子显微镜和扫描电子显微镜观察接种植物木质部细胞中的快速木杆菌细胞，以及通过共聚焦激光扫描显微镜观察，证实了受影响植物中存在快速木杆菌。通过在温室中接种葡萄植株，证实了所选再分离菌株的致病性。通过QPCR估计，PD菌株的每克组织中快速木杆菌细胞的平均水平高于ALSD菌株，这反映了这些菌株在经济宿主中的相对滴度。在未处理的烟草或接种野油菜黄单胞菌（Xanthomonas campestris pv. campestris）或水的烟草中未观察到症状，也未检测到细菌。在该生物测定中，快速木杆菌诱导的症状在接种后2个月内充分表现出来。所描述的生物测定在优化的环境条件下，为研究快速木杆菌菌株（例如，致病性的确认以及PD和ALSD致病型的区分）以及研究快速木杆菌与宿主的相互作用提供了一个有用的系统。烟草品种烟草（Nicotiana tabacum cv. SR1）作为快速木杆菌的生物测定宿主比先前描述的烟草品种哈瓦那（Havana）、RP1和TNN更好。
