Citrus greening or Huanglongbing (HLB) is one of the main devastating citrus diseases worldwide. HLB causing infectious bacterium “Candidatus Liberibacter” is a phloem specific and fastidious agent, having three different species. A comparison of conventional PCR and real-time quantitative PCR (qPCR) was done by universal 16S rDNA marker. In the current study conventional PCR was used to early screening of Candidatus Liberibacter spp and real-time quantitative PCR used for the quantification of HLB causing agent in citrus trees. Total 35 citrus cultivars were selected from mandarins and sweet oranges groups from an orchard “Citrus Research Institute, Sargodha,” Pakistan. The DNA was extracted from HLB asymptomatic and symptomatic leaves. By conventional PCR, the HLB infectious bacterium has identified in 11 sweet oranges samples (31%) in which an amplicon of 1174 bp was generated. While qPCR subsequently reported to quantify the titer of Ca. L.asiaticus in host plant. In the present study qPCR results showed the pathogen could be detected with a Cq value getting in ranged of 26.58to 38.17. Samples with higher Cq ratio showed lower copy number of targeted gene. There was no amplification detected with healthy citrus samples and water control. A robust and sensitive qPCR assay can be used for the screening and quantify the Ca. L. asiaticus strain to confirm the HLB infection in Pakistan. This diagnostic test will be very helpful for implementing a wide range of diagnostics research programs aiming at ultimately developing strategies for the control of HLB in Pakistan.
Keywords: Citrus greening, Conventional PCR, Candidatus Liberibacter asiaticus, Huanglongbing, cytochrome oxidase, real-time qPCR.