Pietersen G, Arrebola E, Breytenbach J H J, Korsten L, le Roux H F, la Grange H, Lopes S A, Meyer J B, Pretorius M C, Schwerdtfeger M, van Vuuren S P, Yamamoto P
University of Pretoria, Pretoria, 0002, South Africa; Citrus Research International, P.O. Box 28, Nelspruit 1200 S.A.; and ARC-Plant Protection Research Institute, Private Bag X134, Queenswood 0121, S.A.
University of Pretoria.
Plant Dis. 2010 Feb;94(2):244-249. doi: 10.1094/PDIS-94-2-0244.
Greening disease of citrus is a serious disease known in South Africa since the late 1920s. In South Africa, it is associated with infection by 'Candidatus Liberibacter africanus', a heat sensitive, phloem-limited, noncultured alpha-proteobacterium. Huanglongbing (HLB), a similar, but more devastating disease that was described initially from China but which now occurs in several citrus producing countries, is associated with a different Liberibacter species, 'Ca. L. asiaticus'. A 'Ca. L. africanus' subspecies, 'Ca. L. africanus subsp. capensis', has been found only in South Africa infecting an indigenous Rutaceous species, Calodendrum capense (Cape Chestnut), in the Western Cape in 1995. The discovery of a new Liberibacter species in Brazil, 'Ca. L. americanus', and the spread of 'Ca. L. asiaticus' to a number of additional countries over the last few years prompted us to assess whether only 'Ca. L. africanus' is present in commercial citrus orchards in South Africa. Samples displaying greening or similar symptoms were collected from 249 citrus trees from 57 orchards distributed throughout the greening affected citrus production areas of South Africa. Multiplex polymerase chain reaction (PCR) was performed on DNA extracts to detect the known citrus Liberibacters. Amplicons were obtained from 197 samples. None of the samples yielded a 1,027-bp amplicon indicative of 'Ca. L. americanus' infection. The amplicons of 84 samples were sequenced, and all were identical to the cognate 'Ca. L. africanus' Nelspruit sequence in GenBank. No instance of 'Ca. L. asiaticus' or 'Ca. L. africanus subsp. capensis' sequence was found. Geographically representative samples that tested negative for Liberibacter also tested negative for phytoplasmas based on real-time PCR results. Based on the results of this survey, it is concluded that to date only 'Ca. L. africanus' is associated with citrus greening in commercial citrus in South Africa.
柑橘黄龙病自20世纪20年代末以来在南非就是一种广为人知的严重病害。在南非，它与“非洲韧皮部杆菌”（‘Candidatus Liberibacter africanus’）感染有关，这是一种对热敏感、局限于韧皮部、无法培养的α-变形菌。黄龙病（HLB）是一种类似但更具毁灭性的病害，最初在中国被描述，现在在几个柑橘生产国均有发生，它与一种不同的韧皮部杆菌“亚洲韧皮部杆菌”（‘Ca. L. asiaticus’）有关。“非洲韧皮部杆菌”的一个亚种“南非非洲韧皮部杆菌”（‘Ca. L. africanus subsp. capensis’）仅在南非被发现，1995年在西开普感染了一种本土芸香科植物——好望角紫檀（Calodendrum capense，即非洲栗）。在巴西发现了一种新的韧皮部杆菌“美洲韧皮部杆菌”（‘Ca. L. americanus’），以及在过去几年里“亚洲韧皮部杆菌”传播到其他一些国家，这促使我们评估南非商业柑橘果园中是否仅存在“非洲韧皮部杆菌”。从南非黄龙病疫区分布的57个果园的249棵柑橘树上采集了表现出黄龙病症状或类似症状的样本。对DNA提取物进行多重聚合酶链反应（PCR）以检测已知的柑橘韧皮部杆菌。从197个样本中获得了扩增子。没有一个样本产生指示“美洲韧皮部杆菌”感染的1027 bp扩增子。对84个样本的扩增子进行了测序，所有序列均与GenBank中同源的“非洲韧皮部杆菌”内尔斯普雷特序列相同。未发现“亚洲韧皮部杆菌”或“南非非洲韧皮部杆菌”序列的实例。基于实时PCR结果，对韧皮部杆菌检测呈阴性的具有地理代表性的样本对植原体检测也呈阴性。根据这项调查的结果，得出的结论是，迄今为止在南非商业柑橘中与柑橘黄龙病相关的仅为“非洲韧皮部杆菌”。
