Bacterial wilt, one of the world's most destructive diseases in many crops, including eucalypt, is caused by four distinct phylogenetic lineages of the Ralstonia solanacearum species complex, recently classified in three distinct species: R. solanacearum (phylotype II), R. pseudosolanacearum (phylotype I and III) and R. syzygii (phylotype IV). In this study, we characterized 93 Ralstonia isolates obtained from eucalypt grown in different Brazilian regions using phylotype and sequevar designations and genomic fingerprinting with BOX-PCR. In addition, we evaluated the aggressiveness of a select group of isolates in two eucalypt clones differing in resistance. We found that 89 isolates belong to R. solanacearum (phylotype II) and four to R. pseudosolanacearum (phylotype I). Unlike R. pseudosolanacearum, R. solanacearum was phylogenetically diverse and no correlation was found between sequevar and geographic origin. Most isolates grouped with reference isolates of phylotype IIA sequevar 41, whereas a few others clustered in phylotype IIB, mainly sequevar 4NPB, which is an emergent variant described affecting eucalypt for the first time. Isolates of R. solanacearum phylotype IIB were less aggressive to clone CLR371 (susceptible) whereas the R. pseudosolanacearum isolate tested was the only one pathogenic to the CLR172 (resistant) clone. Isolate aggressiveness varied between the eucalypt clones tested. The results of this study reinforce the importance of conducting molecular and aggressiveness characterization of the pathogen population to develop management strategies aimed at the deployment of host resistance in eucalypt breeding programmes.

中文翻译：

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Eucalyptus spp. 青枯病菌种复合物的分子特征和侵袭性。在巴西

青枯病，在许多作物，包括桉树是世界上最具破坏性的疾病之一，是由四个不同的进化谱系导致青枯雷尔氏菌品种繁杂，最近分为三个不同的种类：青枯菌（种系型II），R. pseudosolanacearum（系统发育型 I 和 III) 和R. syzygii (系统发育型 IV)。在这项研究中，我们使用系统发育型和序列变异命名以及使用 BOX-PCR 的基因组指纹识别从生长在不同巴西地区的桉树中提取了93株Ralstonia分离株。此外，我们在两个抗性不同的桉树克隆中评估了一组精选分离株的侵袭性。我们发现 89 个分离株属于R. solanacearum (phylotype II) 和四个到R. pseudosolanacearum (phylotype I)。与R. pseudosolanacearum不同，R. solanacearum在系统发育上是多样的，并且在序列变种和地理起源之间没有发现相关性。大多数分离株与系统发育型 IIA sequevar 41 的参考分离株分组，而其他一些则聚集在系统发育型 IIB 中，主要是 sequevar 4NPB，这是首次描述影响桉树的紧急变异。R. solanacearum系统发育型 IIB 的分离株对克隆 CLR371（易感）的攻击性较低，而R. pseudosolanacearum测试的分离株是唯一一种对 CLR172（抗性）克隆致病的菌株。所测试的桉树克隆之间的分离攻击性不同。这项研究的结果强调了对病原体种群进行分子和侵袭性表征以制定旨在在桉树育种计划中部署宿主抗性的管理策略的重要性。