This study was undertaken to characterize the alpha
subgroup of the proteobacteria causing the
huanglongbing (HLB) disease of citrus from three
different ecological zones of Kenya namely the Lower
highlands (LH2, LH3, 1800-1900 m above sea level); Upper midlands (UM3, UM4, 1390-1475m), Lower
midlands (LM5, LM4, LM3 of 1290-1340-1390m), by
isolation and sequencing DNA encoding the L10 and
L12 ribosomal proteins and the intergenic region. A
7I6-basepair DNA fragment was amplified and sequenced and consisted of 536 basepairs of DNA
encoding the L10 protein, 44 basepairs of DNA
intergenic region and 136 basepairs of DNA that
partially encodes the L12 protein. Sequences of
rpL10/L12 protein genes from Kenyan strains were
98% and 81% similar to the South African '
Candidatus
Liberibacter africanus strain Nelspruit' and the Asian
'
Candidatus Liberibacter asiaticus' strains, respectively.
The intergenic rDNA sequence of Kenyan strain from
UM and LM showed 84% similarity with '
Candidatus L.
africanus strain Nelspruit' and 50% similarity with
'
Candidatus L. asiaticus' strain. However, the LH strain
had an 11- basepairs deletion, while the LM4 had a 5-
basepair deletion in the intergenic region compared to
'
Candidatus L. africanus strain Nelspruit'. The L10
amino acid sequence was 100% homologous among
HLB bacteria obtained from the agro-ecological zones
in Kenya and the L10 protein sequence was also
homologus to '
Candidatus L. africanus strain Nelspruit'.
Nevertheless, the L10 amino acid sequence of
'
Candidatus L. asiaticus' and the '
Candidatus L.
africanus subsp. capensis' differed from the Kenyan
strains by 18.36% and 11.82%, respectively.
Phylogenetic analysis of both the L10/L12 rDNA
sequences and the L10 amino acid sequences clustered
the Kenyan strains of the '
Candidatus Liberibacter'
species with members of alpha subdivision of
proteobacteria.
