Almeida Rodrigo P P, Purcell Alexander H
Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720, USA.
Appl Environ Microbiol. 2003 Dec;69(12):7447-52. doi: 10.1128/AEM.69.12.7447-7452.2003.
Xylella fastidiosa is a xylem-limited bacterium that causes various diseases, among them Pierce's disease of grapevine (PD) and almond leaf scorch (ALS). PD and ALS have long been considered to be caused by the same strain of this pathogen, but recent genetic studies have revealed differences among X. fastidiosa isolated from these host plants. We tested the hypothesis that ALS is caused by PD and ALS strains in the field and found that both groups of X. fastidiosa caused ALS and overwintered within almonds after mechanical inoculation. Under greenhouse conditions, all isolates caused ALS and all isolates from grapes caused PD. However, isolates belonging to almond genetic groupings did not cause PD in inoculated grapes but systemically infected grapes with lower frequency and populations than those belonging to grape strains. Isolates able to cause both PD and ALS developed 10-fold-higher concentrations of X. fastidiosa in grapes than in almonds. In the laboratory, isolates from grapes overwintered with higher efficiency in grapes than in almonds and isolates from almonds overwintered better in almonds than in grapes. We assigned strains from almonds into groups I and II on the basis of their genetic characteristics, growth on PD3 solid medium, and bacterial populations within inoculated grapevines. Our results show that genetically distinct strains from grapes and almonds differ in population behavior and pathogenicity in grapes and in the ability to grow on two different media.
桑萎蔫病菌是一种局限于木质部的细菌，可引发多种疾病，其中包括葡萄皮尔氏病（PD）和杏仁叶焦病（ALS）。长期以来，PD和ALS一直被认为是由该病原菌的同一菌株引起的，但最近的遗传学研究揭示了从这些寄主植物中分离出的桑萎蔫病菌之间存在差异。我们对ALS由PD和ALS菌株在田间引起这一假设进行了测试，发现这两组桑萎蔫病菌在机械接种后均能引发ALS并在杏仁内越冬。在温室条件下，所有分离株均能引发ALS，所有来自葡萄的分离株均能引发PD。然而，属于杏仁基因分组的分离株在接种的葡萄中不会引发PD，但与属于葡萄菌株的分离株相比，其对葡萄的系统感染频率和菌量较低。能够引发PD和ALS的分离株在葡萄中形成的桑萎蔫病菌浓度比在杏仁中高10倍。在实验室中，来自葡萄的分离株在葡萄中的越冬效率高于在杏仁中，而来自杏仁的分离株在杏仁中的越冬情况比在葡萄中更好。我们根据杏仁菌株的遗传特征、在PD3固体培养基上的生长情况以及接种葡萄藤内的细菌数量，将其分为I组和II组。我们的结果表明，来自葡萄和杏仁的基因不同的菌株在葡萄中的群体行为、致病性以及在两种不同培养基上的生长能力存在差异。
