Pseudomonas is a highly diverse genus that includes species that cause disease in both plants and animals. Recently, pathogenic pseudomonads from the Pseudomonas syringae and Pseudomonas fluorescens species complexes have caused significant outbreaks in several agronomically important crops in Turkey, including tomato, citrus, artichoke and melon. We characterized 169 pathogenic Pseudomonas strains associated with recent outbreaks in Turkey via multilocus sequence analysis and whole-genome sequencing, then used comparative and evolutionary genomics to characterize putative virulence mechanisms. Most of the isolates are closely related to other plant pathogens distributed among the primary phylogroups of P. syringae , although there are significant numbers of P. fluorescens isolates, which is a species better known as a rhizosphere-inhabiting plant-growth promoter. We found that all 39 citrus blast pathogens cluster in P. syringae phylogroup 2, although strains isolated from the same host do not cluster monophyletically, with lemon, mandarin orange and sweet orange isolates all being intermixed throughout the phylogroup. In contrast, 20 tomato pith pathogens are found in two independent lineages: one in the P. syringae secondary phylogroups, and the other from the P. fluorescens species complex. These divergent pith necrosis strains lack characteristic virulence factors like the canonical tripartite type III secretion system, large effector repertoires and the ability to synthesize multiple bacterial phytotoxins, suggesting they have alternative molecular mechanisms to cause disease. These findings highlight the complex nature of host specificity among plant pathogenic pseudomonads.

中文翻译：

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土耳其植物致病性假单胞菌流行病学和毒力的比较基因组学见解

假单胞菌属 是一个高度多样化的属，包括引起植物和动物疾病的物种。最近，来自Pseudomonas syringae和Pseudomonas fluorescens物种复合体的致病性假单胞菌在土耳其的几种重要农作物中引起了重大爆发，包括番茄、柑橘、朝鲜蓟和甜瓜。我们通过多位点序列分析和全基因组测序表征了与土耳其近期爆发相关的 169 种致病性假单胞菌菌株，然后使用比较和进化基因组学来表征推定的毒力机制。大多数分离株与分布在丁香假单胞菌主要系统群中的其他植物病原体密切相关。 ，尽管有大量荧光假单胞菌分离物，它是一种更为人所知的根际栖息植物生长促进剂。我们发现所有 39 种柑橘瘟病病原体都聚集在P. syringae phylogroup 2 中，尽管从同一宿主分离的菌株不会单系聚集，柠檬、橘子和甜橙分离物在整个系统群中都混合在一起。相比之下，在两个独立的谱系中发现了 20 种番茄髓病原体：一种在P. syringae次级系统群中，另一种来自P. fluorescens 物种复杂。这些不同的髓坏死菌株缺乏特征性毒力因子，如典型的三方 III 型分泌系统、大型效应器库和合成多种细菌植物毒素的能力，这表明它们具有引起疾病的替代分子机制。这些发现突出了植物致病性假单胞菌宿主特异性的复杂性。