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
278C. capense samples were collected throughout
South Africa and tested for Liberibacters using realtime
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 ßoperon
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
44C. capense and 272 citrus (Midnight Valencia) trees
growing in close proximity to each other for over
15 years was determined. Out of 44C. 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.
