Andrographis paniculata (Family Acanthaceae), also called Kalmegh, is a medicinal herb in India well-known for its various pharmaceutical properties (1). In August 2012, during a survey in the northern parts of India, several Kalmegh plants in Barabanki District of Uttar Pradesh Province showed typical virus-like symptoms along with prominent lethal leaf yellowing. The infected plants initially showed some chlorotic streaks, which later turned completely yellow, ultimately leading to premature death. Mechanical/sap inoculation failed to transmit the pathogen. Based on the symptomology, a heavy infestation of whiteflies (Bemisia tabaci) in the infected fields, and lack of mechanical transmission, the association of a begomovirus was suspected. The disease incidence was calculated to be about 15 to 20% on the basis of plant population. Twenty samples from naturally infected plants of A. paniculata were collected from various field locations. Total genomic DNA from the symptomatic and non-symptomatic samples was isolated by the modified CTAB method (4). The initial PCR-based detection was performed using begomovirus coat protein gene specific primers (forward 5′-ATGGCGAAGCGACCAG-3′ and reverse 5′-TTAATTTGTGACCGAATCAT-3′), which generated an amplicon of 771 bp in most of the (17/20) symptomatic samples. No amplification was obtained in healthy or non-symptomatic plant samples. The full-length genome was amplified via rolling-circle amplification (RCA) according to the manufacturer's instructions using random hexamer primers and φ29 DNA polymerase. A portion of the RCA product (1 μl) was subjected to digestion with different restriction enzymes, out of which BamHI yielded DNA fragments of approximately 2.7 and 1.3 kb, corresponding to DNA-A and β satellite molecules, respectively. These fragments were eluted from the gel and cloned into the suitable restriction site of pGreen0029 vector. The positive clones were checked by restriction digestion. Twelve out of 20 clones were found to be positive and sequenced. The complete genome sequences of DNA A (2,754 bp) and β (1,366 bp) satellites were deposited in the GenBank database with the accession numbers KM359406 and KM359407, respectively. The absence of DNA-B molecule was ascertained, as no PCR amplification was detected with DNA-B-specific primers. Sequence analysis showed highest nucleotide identity (90%) with Catharanthus yellow mosaic virus (CYMV) (HE580234) and ≤85% identity with other begomoviruses of the database. Sequence analysis of the associated betasatellite showed 96% identity with Andrographis yellow vein leaf curl betasatellite (KC967282). CYMV was first reported on Catharanthus roseus with no associated betasatellite from Pakistan (2). However, this is the first report of CYMV along with a betasatellite infecting A. paniculata in India. Recently a begomovirus (Eclipta yellow vein virus) infection was reported on A. paniculata in association with Andrographis yellow vein leaf curl betasatellite from India for the first time (3); now the crop has also become a host of CYMV. Thus, this study highlights the spread of CYMV from its preliminary host to a new host plant (A. paniculata), across the South Asian countries. Therefore, it is important to take measures for the management of its transmitting vector so as to curtail the spread of the virus to new economically and commercially important crops.
References: (1) S. Akbar. Altern. Med. Rev. 16:1, 2011. (2) M. Ilyas et al. Arch. Virol. 158:505, 2013. (3) A. Khan and A. Samad. Plant Dis. 98:698, 2014. (4) S. P. S. Khanuja et al. Plant Mol. Biol. Rep. 17:1, 1999.