A new bacterium, ‘Canditatus Liberibacter americanus’ is associated with citrus greening in Brazil
As reported earlier, symptoms of citrus greening (or Huanglongbing) have recently been observed in Brazil, in São Paulo State (EPPO RS 2004/103, 2004/145) and studies are being done to identify the causal agent(s). 43 symptomatic and 25 asymptomatic samples of sweet orange (Citrus sinensis) were tested for the presence of ‘Canditatus Liberibacter africanus’ and ‘Canditatus Liberibacter asiaticus’ by PCR with specific primers for both bacteria. All results were negative. However, when testing the same samples by PCR with universal primers for the amplification of bacterial 16S rDNA, all symptomatic samples gave a positive results (but not the asymptomatic ones), thus confirming the presence of a bacterium. The 16S rDNA product was cloned, sequenced and compared with those of ‘Ca. L. africanus’ and ‘Ca. L. asiaticus’. While the 16S rDNA sequence of these two species of Liberibacter have 97.5% sequence identity, the 16S rDNA sequence of the new bacterium shared only 93.7 % identity with that of ‘Ca. L. asiaticus’ and 93.9 % with that of ‘Ca. L. africanus’. In addition, the secondary structure of the 16S rDNA possessed the characteristic features of Liberibacter species. The authors considered that the studied bacterium is a new and distinct Liberibacter, tentatively called ‘Canditatus Liberibacter americanus’. Specific primers were then developed for the detection of this new species. During further surveys, the new bacterium was detected in 214 symptomatic leaf samples collected from 47 farms in 35 municipalities, while ‘Ca. L. asiaticus’ was only found 4 times within these 47 farms.
Sources
Texeira DC, Ayres J, Kitajima EW, Danet L, Jagoueix-Eveillard S, Saillard C, Bové JM (2005) First report of a Huanglongbing-like disease of Citrus in Sao Paulo State, Brazil and association of a new Liberibacter species ‘Candidatus Liberibacter americanus’, with the disease.
Plant Disease, 89(1), p 107.