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First Report of the Huanglongbing Bacterium ‘Candidatus Liberibacter asiaticus’ Infecting Satkara (Citrus macroptera) in India

    Authors and Affiliations
    • A. K. Das
    • A. Kumar , National Research Centre for Citrus, Amravati Road, Nagpur 440 010, Maharashtra, India

      Published Online:https://doi.org/10.1094/PDIS-94-3-0375A

      In India, satkara (Citrus macroptera) is found in the northeastern regions of Shella and Dowki near Cherrapunji in Meghalaya, the Jampui Hills of Tripura and Mizoram, and the Chendel District of Manipur. Locally, it is called satkara because ‘sat’ refers to multiples of seven and the fruit generally contains fourteen segments. The fruit is used in the preparation of pickles and its oil is used in the perfume industry. In January 2007, in Behliangchhip, Jampui Hills, Tripura, India, we noticed seven satkara trees of 26 showing leaf mottling and yellowing in young shoots, symptoms typical of huanglongbing (HLB). HLB is a destructive citrus disease caused by a nonculturable, phloem-limited alpha-proteobacterium of the genus ‘Candidatus Liberibacter’. Among the three known ‘Ca. Liberibacter’ species (Ca. Liberibacter asiaticus, Ca. L. africanus, and Ca. L. americanus), only Ca. L. asiaticus has been reported in India (1) but not from satkara. To identify the pathogen, total DNA was extracted and purified from 200 mg of leaf midribs from five symptomatic and five symptomless trees with the DNeasy Plant Mini Kit (Qiagen, Gmbh, Hilden, Germany) as per the manufacturer's instructions. Samples were tested for ‘Ca. L. asiaticus’ by PCR with primer sets OI1/OI2c targeting the 16S rDNA locus (3) and A2/J5 targeting the beta-operon locus of ribosomal proteins (2). DNA samples from all symptomatic leaves were positive with both primer sets. The OI1/OI2c primers generated an amplicon of approximately 1,160 bp and digestion of the amplicon by XbaI yielded two DNA fragments of approximately 640 bp and 520 bp, suggesting the presence of ‘Ca. L. asiaticus’(3). The A2/J5 primer set generated an ~703-bp amplicon, indicating ‘Ca. L. africanus’ was not present. No DNA was amplified from the asymptomatic satkara trees. One each of the OI1/OI2c and A2/J5 amplicons was purified, cloned (pGEM-T Easy vector, Promega, Hampshire, UK) and sequenced (Bangalore Genei, Bengaluru, Karnataka, India). The derived sequences, 1167 bp for the OI1/OI2c amplicon and 703 bp for the A2/J5 amplicon, have been deposited in the GenBank database under Accession Nos. GQ369792 and GU074017, respectively. Sequence comparison revealed that GQ369792 and GU074017 shared >99% identity to the corresponding regions of ‘Ca. L. asiaticus’ in the GenBank database. No DNA was amplified by PCR with primer set GB1/GB2 (4) specific for ‘Ca. L. americanus’. To our knowledge, this is the first report of molecular identification of ‘Ca. L. asiaticus’ infecting satkara in India.

      References: (1) A. K. Das. Curr. Sci. 87:1183, 2004. (2) A. Hocquellet et al. Mol. Cell. Probes 13:373, 1999. (3) S. Jagoueix et al. Mol. Cell. Probes 10:43, 1996. (4) D. C. Teixeira et al. Mol. Cell. Probes 19:173, 2005.