DISEASE INTENSITY OF HUANGLONGBING IN SEVERAL CITRUS PLANTATIONS IN WEST JAVA AND IDENTIFICATION OF ITS CAUSAL AGENT

Abstract

Citrus (Citrus sp.) is a horticultural commodity with high demand in Indonesia. National citrus production and productivity have declined due to a dangerous disease, Huanglongbing (HLB). HLB is caused by an obligate pathogenic bacteria Candidatus Liberibacter asiaticus (CLas) which is transmitted by insect vector Diaphorina citri and vegetative propagation. The objective of this study was to describe the intensity of HLB disease in citrus plants in West Java and determine the presence and identity of the causative pathogen using PCR-sequencing. The study was conducted by observing disease intensity in the field, measuring the leaf dimension and ratio, and detecting the causative agent using Polymerase chain reaction (PCR) based on bacterial 16S rRNA gene and its nucleotide sequencing. HLB symptoms found in the field include asymmetric leaf chlorosis between the left and right sides of the leaf veins, thickening of the leaf veins, and yellowing of the plant shoots. The incidence of HLB disease ranges from 96% to 100%, and the severity ranges from 36.8% to 60%. Bacteria Ca. L.asiaticus was successfully detected using the PCR method in citrus leaf samples originating from the HAS Farm, Hj. Dayat, Inoy Dekopon, Bosaga Chokun, and Mandalawangi citrus orchards with the highest percentage of identity close to 100% with strain accessions available in GenBank. From Phylogenetic tree analysis, samples from West Javanese i.e. HSF 90, DKPIN 90, DKPIN 20, MDL 60, BSGCHKN 90, and DYT 90, were in the same cluster with accessions from India, the United States, China, Mexico, Saudi Arabia, Iran, and Pakistan, while the HSF 20 and HSF 50 samples were separate and formed their own cluster.