A novel subspecies of 'Candidatus Liberibacter africanus' found on native Teclea gerrardii (Family : Rutaceae) from South Africa

Abstract

The phloem limited bacterium „Candidatus Liberibacter africanus‟ is associated with citrus greening disease in South Africa. This bacterium has been identified solely from commercial citrus in Africa and the Mascarene islands, and its origin may lie within an indigenous rutaceous host from Africa. Recently, in determining whether alternative hosts of Laf exist amongst the indigenous rutaceous hosts of its triozid vector, Trioza erytreae, three novel subspecies of Laf were identified i.e. „Candidatus Liberibacter africanus subsp. clausenae‟, „Candidatus Liberibacter africanus subsp. vepridis‟ and „Candidatus Liberibacter africanus subsp. zanthoxyli‟ in addition to the formerly identified „Candidatus Liberibacter africanus subsp. capensis‟. The current study expands upon the range of indigenous rutaceous tree species tested for liberibacters closely related to Laf and its subspecies. A collection of 121 samples of Teclea and Oricia species were sampled from Oribi Gorge and Umtamvunu nature reserves in KwaZulu Natal. Total DNA was extracted and the presence of liberibacters from these samples determined using a generic liberibacter TaqMan real-time PCR assay. Liberibacters from positive samples were further characterised through amplification and sequencing of the 16S rRNA, outer-membrane protein (omp) and 50S ribosomal protein L10 (rplJ) genes. A single Teclea gerrardii specimen tested positive for a liberibacter and, through phylogenetic analyses of the three genes sequenced, was shown to be unique, albeit closely related to „Ca. L. africanus‟ and „Ca. L. africanus subsp. zanthoxyli‟. We propose that this newly identified liberibacter be named „Candidatus Liberibacter africanus subsp. tecleae‟.