1 Departamento de Pesquisa & Desenvolvimento, Fundecitrus, Araraquara, SP, 14807-040 and PPG Biotecnologia, IQ/UNESP Araraquara, SP, 14800-060. Brazil.
2 Departamento de Pesquisa & Desenvolvimento, Fundecitrus, Araraquara, SP, 14807-040, Brazil.
Phytopathology. 2019 Mar;109(3):366-374. doi: 10.1094/PHYTO-03-18-0081-R. Epub 2019 Feb 4.
When huanglongbing (HLB) was found in Brazil in 2004, 'Candidatus Liberibacter americanus' was infecting most of the trees while 'Ca. L. asiaticus' was present in a minor proportion. Currently, 'Ca. L. asiaticus' is the predominant bacterium associated with HLB in citrus trees in São Paulo (SP) and Minas Gerais (MG) States, the major citrus-growing regions in Brazil. A phytoplasma from the 16SrIX group was associated with HLB symptoms in Brazil in 2007, in plants free of Liberibacter spp. In this report, HLB samples testing negative for 'Ca. L. asiaticus', 'Ca. L. americanus', and 16SrIX phytoplasma were infected with 16SrIII phytoplasmas. Coinfection with 'Ca. L. asiaticus' and 16SrIII was also found. The 16S ribosomal RNA (rRNA) gene sequences from 22 samples were obtained and sequenced, confirming that the 16SrIII group phytoplasma is associated with HLB symptoms in SP and MG States. Ten single-nucleotide polymorphisms (SNPs) were found in the 1,427-bp 16S rRNA gene sequences from 16SrIII phytoplasmas from citrus, whereas none was detected in 16S rRNA gene sequences among 16SrIX phytoplasma from citrus. Ribosomal protein (rp) rpsSrplVrpsC gene sequences were amplified with 16SrIII group-specific primers, sequenced from a subset of nine samples, and assembled into three groups based on eight SNPs. SNPs in 16S rRNA gene and rp gene sequences are common in 16SrIII phytoplasmas from other hosts and this phytoplasma group is widespread in South America. 16SrIII phytoplasmas highly related are commonly found in Melia azedarach, a widespread tree in Brazil and Argentina. The finding of a new phytoplasma associated with HLB symptoms belonging to the 16SrIII group reinforces the need to develop diagnostic tools to assess HLB-associated microbiomes.
2004 年，黄龙病（HLB）在巴西被发现时，“Candidatus Liberibacter americanus”正在感染大多数树木，而“Ca. L. asiaticus”则存在于较小的比例。目前，“Ca. L. asiaticus”是巴西圣保罗（SP）和米纳斯吉拉斯（MG）州柑橘树上与 HLB 相关的主要细菌，这两个州是巴西主要的柑橘种植区。2007 年，在巴西与 HLB 症状相关的植物中发现了一种属于 16SrIX 组的植原体，而这些植物中没有 Liberibacter spp。在本报告中，检测到“Ca. L. asiaticus”、“Ca. L. americanus”和 16SrIX 植原体均为阴性的 HLB 样本感染了 16SrIII 植原体。还发现了“Ca. L. asiaticus”和 16SrIII 的共感染。从 22 个样本中获得并测序了 16S 核糖体 RNA（rRNA）基因序列，证实了 16SrIII 组植原体与 SP 和 MG 州的 HLB 症状有关。从柑橘中分离到的 16SrIII 植原体的 16S rRNA 基因序列中有 10 个单核苷酸多态性（SNP），而在柑橘中的 16SrIX 植原体的 16S rRNA 基因序列中未检测到 SNP。用 16SrIII 组特异性引物扩增核糖体蛋白（rp）rpsSrplVrpsC 基因序列，从 9 个样本中选择了一部分进行测序，并根据 8 个 SNP 将其组装成三个组。其他宿主的 16SrIII 植原体中普遍存在 16S rRNA 基因和 rp 基因序列中的 SNP，并且该植原体组在南美洲广泛分布。在巴西和阿根廷广泛存在的臭椿中，发现了与 HLB 症状相关的、高度相关的 16SrIII 植原体。发现与 HLB 症状相关的、属于 16SrIII 组的新植原体，这再次强调了开发评估与 HLB 相关微生物组的诊断工具的必要性。
