Fritschi Felix B, Lin Hong, Walker M Andrew
Division of Plant Sciences, University of Missouri, Columbia 65211.
United States Department of Agriculture-Agricultural Research Service, Crop Diseases, Pests & Genetics Research Unit, Parlier, CA 93648.
Plant Dis. 2008 Feb;92(2):276-286. doi: 10.1094/PDIS-92-2-0276.
The xylem-limited bacterium Xylella fastidiosa causes Pierce's disease (PD), whose disease symptoms are primarily the result of xylem vessel blockage in susceptible grapevines. Stem internode and petiole tissues from infected and uninfected control plants of four grape genotypes (Vitis vinifera, V. rufotomentosa, V. smalliana, and V. arizonica/candicans) differing in PD susceptibility were examined using scanning electron microscopy (SEM). Tyloses, fibrillar networks, and gum plugs were observed in lumens of tracheary elements in petioles and internodes of both water-inoculated control plants and X. fastidiosa-inoculated plants of all genotypes. Bacteria were not observed in control plants. In both petiole and internode tissues, the greatest number of occluded xylem vessels were observed in V. vinifera and the smallest number in V. arizonica/candicans. The number of xylem vessels infested with X. fastidiosa was greatest in V. vinifera and did not differ among the other three genotypes. Systemic infection was found in all genotypes. The frequency with which X. fastidiosa infested vessels were observed using SEM corresponded well with bacterial levels estimated by enzyme-linked immunosorbent assay. Among infected plants, tylose formation in internodes was lowest in V. arizonica/candicans and did not differ among the other three genotypes. Infection with X. fastidiosa strongly induced tylose formation in V. vinifera and V. smalliana but not in V. arizonica/candicans. Analysis across tissues and genotypes indicated an induction of fibrillar networks and gum occlusions in response to X. fastidiosa infection, whereas treatment comparisons within genotypes were not significant except for V. vinifera petioles. Limiting the spread of X. fastidiosa infection by xylem conduit occlusions does not appear to be the mechanism conferring PD resistance or tolerance to V. arizonica/candicans, V. smalliana, or V. rufotomentosa. In contrast, the strong induction of tyloses may be detrimental rather than beneficial for V. vinifera survival after X. fastidiosa infection.
木质部受限细菌——葡萄黄化病菌（Xylella fastidiosa）引发皮尔斯病（PD），该病症状主要是易感葡萄藤木质部导管堵塞所致。利用扫描电子显微镜（SEM）对四种葡萄基因型（欧洲葡萄、绒毛葡萄、小叶葡萄和亚利桑那葡萄/坎迪肯葡萄）中感染和未感染的对照植株的茎节间和叶柄组织进行了检查，这四种基因型对皮尔斯病的易感性各不相同。在所有基因型的水接种对照植株和接种葡萄黄化病菌的植株的叶柄和节间的管状分子腔中均观察到侵填体、纤维状网络和树胶塞。在对照植株中未观察到细菌。在叶柄和节间组织中，欧洲葡萄中观察到的被堵塞的木质部导管数量最多，而亚利桑那葡萄/坎迪肯葡萄中最少。感染葡萄黄化病菌的木质部导管数量在欧洲葡萄中最多，在其他三种基因型中无差异。在所有基因型中均发现了系统感染。利用扫描电子显微镜观察到葡萄黄化病菌侵染导管的频率与酶联免疫吸附测定法估计的细菌水平高度吻合。在受感染植株中，亚利桑那葡萄/坎迪肯葡萄节间的侵填体形成最少，在其他三种基因型中无差异。葡萄黄化病菌感染强烈诱导欧洲葡萄和小叶葡萄形成侵填体，但对亚利桑那葡萄/坎迪肯葡萄则无此作用。跨组织和基因型的分析表明，葡萄黄化病菌感染会诱导纤维状网络和树胶堵塞的形成，而除欧洲葡萄叶柄外，基因型内的处理比较无显著差异。通过木质部导管堵塞来限制葡萄黄化病菌感染的传播似乎不是亚利桑那葡萄/坎迪肯葡萄、小叶葡萄或绒毛葡萄对皮尔斯病产生抗性或耐受性的机制。相反，侵填体的强烈诱导对葡萄黄化病菌感染后的欧洲葡萄存活可能有害而非有益。
