Widespread occurrence of “Candidatus liberibacter africanus subspecies capensis” in Calodendrum capense in South Africa

Abstract

Recent studies in citrus orchards confirmed that Citrus Greening, a heat sensitive citrus disease, similar to Huanglongbing (HLB), is associated with the presence of “Candidatus Liberibacter africanus” (Laf) in South Africa. Neither “Candidatus Liberibacter asiaticus” (Las), associated with HLB, “Candidatus Liberibacter americanus”, nor “Candidatus Liberibacter africanus ssp. capensis” (LafC), previously detected in the Western Cape, South Africa on an indigenous Rutaceous species, Calodendrum capense (L. f.) Thunb. (Cape Chestnut), were detected in citrus. The current study aims to determine the potential role of C. capense in the epidemiology of Citrus Greening in South Africa and whether LafC poses a risk to citriculture. A total of 278 C. capense samples were collected throughout South Africa and tested for Liberibacters using real-time PCR. While LafC was found in 100 samples, distributed from all areas where collected, no evidence of Laf infection in any sample was found . The identity of the LafC present was confirmed by sequencing the amplicon derived from conventional PCR of the ß-operon of the ribosomal protein gene region of the first 17 infected trees found and of a representative sample from each district. The Liberibacter status of 44 C. capense and 272 citrus (Midnight Valencia) trees growing in close proximity to each other for over 15 years was determined. Out of 44 C. capense specimens, 43 were infected with LafC, but none of the citrus trees were infected with LafC. Based on the results of this it appears that natural spread of LafC to citrus does not occur.