The objective of the present study was to detect presence of pathogenic fastidious bacterium, Candidatus Liberibacter asiaticus using PCR from leaves of Siam citrus showing Citrus Vein Phloem Degeneration (CVPD) symptoms in Singkawang City plantation, Pontianak, West Kalimantan, Indonesia. Citrus leaf samples were collected based on visual observation of symptoms showing CVPD infection. Typical symptoms of CVPD include leaf yellowing (chlorosis), vein banding, leaves become stiff, thicker and smaller in size. The pathogenic bacterium, Candidatus Liberibacter asiaticus was detected using two specific primers, namely, OI1/ OI2c amplified 16S rRNA gene and A2/J5, amplified ribosomal  protein gene of the rplKAJL-rpoBC operon (β-operon). PCR amplification detected the presence of 1100 bp band using OI1/ OI2c primers, and 703 bp band using A2/J5 primers from symptomatic Siam citrus leaves. PCR products were not detected from healthy plants serve as control. By using two sets of specific primers to amplify 16S rRNA gene and ribosomal protein gene, Candidatus Liberibacter asiaticus was detected in symptomatic Siam citrus leaves in Singkawang City, Pontianak, Indonesia. Detection of the bacterial pathogen causing CVPD is important to prevent spreading of the disease which could affect production of citrus fruits.

Liberibacter bacteria are one of the pathogenic bacteria in citrus plants. Siam Citrus Plant in Setapok Village, Singkawang City, suspected to be infected with Liberibacter spp. bacteria by showing patterns of symptoms of chlorosis accompanied by patches. This study aims to detect Liberibacter spp. on Siam Citrus leaves with symptomatic chlorosis with patches. Leaf sampling uses the roaming method in one of the citrus plantations in Setapok Village, Singkawang City. Detection of Liberibacter spp. done by PCR (Polymerase Chain Reaction) technique. Detection of bacterial DNA through several stages namely, isolation of bacterial plasmid DNA, 16S rDNA gene amplification with a thermocycler machine, and visualization using a set of electrophoresis devices. Electrophoresis results show the presence of DNA band lines, with a size of around 1100 bp for OI1 and OI2c primers, and DNA bands of 703 bp for A2 and J5 specifics. The results showed that there were Liberibacter spp. in the symptomatic chlorosis of Siam Citrus leaves accompanied by patches.

Keywords: