Swanson Jill K, Montes Luis, Mejia Luis, Allen Caitilyn
Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706.
Faculty of Agronomy, University of San Carlos, Guatemala City, Guatemala.
Plant Dis. 2007 Jul;91(7):828-834. doi: 10.1094/PDIS-91-7-0828.
Ralstonia solanacearum race 3 biovar 2 is a regulated quarantine pathogen that infects solanaceous hosts such as potato as well as geranium, where it causes either bacterial wilt (also known as Southern Wilt) or a symptomless latent infection. Geranium growers and government regulators need reliable detection methods to identify infected plant material before it is exported. We previously found that R. solanacearum-infected geranium plants can shed millions of bacteria in effluent water that flows from pots. We tested a nondestructive sampling method wherein effluent water from infected plants grown under commercial conditions was both dilution plated and filter concentrated for real-time polymerase chain reaction (PCR). Under field conditions in Guatemala, effluent shedding of infected geranium plants was highly variable. Comprehensive growth chamber studies confirmed that latently infected and mildly symptomatic geranium plants often but not invariably shed detectable numbers of bacteria in their effluent. At the peak of bacterial shedding, just under 90% of infected plants shed detectable bacteria whereas, at the lowest point, 44% shed detectable numbers of pathogen cells. Bacterial shedding peaked several weeks after inoculation regardless of whether plants were symptomatic or latently infected. Bacterial stem population sizes did not correlate with either effluent population sizes or disease index rating. Finally, we found that the effluent from geranium plants grown in volcanic rock scoria medium contains inhibitors that reduce the effectiveness of real-time PCR detection methods.
青枯雷尔氏菌3号小种2型生物变种是一种受管制的检疫性病原菌，可感染茄科寄主，如马铃薯以及天竺葵，在这些寄主上会引发青枯病（也称为南方枯萎病）或无症状的潜伏感染。天竺葵种植者和政府监管机构需要可靠的检测方法，以便在受感染的植物材料出口前进行识别。我们之前发现，受青枯雷尔氏菌感染的天竺葵植株会在从花盆流出的废水中释放数百万个细菌。我们测试了一种非破坏性采样方法，即将商业条件下种植的受感染植物的废水进行稀释平板培养和过滤浓缩，用于实时聚合酶链反应（PCR）检测。在危地马拉的田间条件下，受感染天竺葵植株的废水细菌释放量差异很大。综合生长室研究证实，潜伏感染和症状轻微的天竺葵植株通常但并非总是在其废水中释放可检测数量的细菌。在细菌释放高峰期，近90%的受感染植株释放出可检测到的细菌，而在最低点时，44%的植株释放出可检测数量的病原菌细胞。无论植株是有症状还是潜伏感染，接种后几周细菌释放量达到峰值。细菌在茎中的数量与废水细菌数量或病情指数评级均无相关性。最后，我们发现生长在火山岩火山渣培养基中的天竺葵植株的废水含有抑制剂，会降低实时PCR检测方法的有效性。
