First Report on the Molecular Identification of Phytoplasma (16SrII-D) Associated with Witches' Broom of Kalmegh (Andrographis paniculata) in India.

Abstract

Andrographis paniculata (family Acanthaceae), also known as "King of Bitters" or Kalmegh, is an important medicinal plant used for the treatment of various diseases. It has antimicrobial, antiviral, anti-inflammatory, hepatoprotective, antidiabetic, antihyperglycemic, and antioxidant properties (1). During June 2014, while performing a routine survey of the commercial trial fields of Kalmegh at Central Institute of Medicinal and Aromatic Plants (CIMAP), Lucknow, India, typical phytoplasma disease symptoms such as virescence, proliferation, and witches' broom along with little leaf and stunted growth were observed. The disease incidence was estimated to be approximately 7 to 10%. To ascertain the presence of phytoplasma, 16 samples of leaves were collected from nine different field sites, and total genomic DNA was extracted from the symptomatic and symptomless Kalmegh plants by the CTAB method. Direct and nested PCR assays were performed targeting the 16S rDNA using generic phytoplasma primer pairs P1/P6 followed by R16F2n/R16R2 (2). Resulting bands of the expected size (1.5 kb and 1.2 kb, respectively) were amplified from symptomatic plants. No amplification was observed with DNA from asymptomatic plant samples. The purified nested PCR products were cloned into E. coli DH5α, using the pGEM-T Easy vector (Promega, United States) and sequenced with primers M13For/M13Rev using an automatic sequencer (ABI Prism, Perkin Elmer) at CIMAP. The sequence was analyzed by BLASTn and found to share 99% similarity with Echinacea witches'-broom phytoplasma and Sesame phyllody phytoplasma strain (GenBank Accession Nos. JF340080 and KF612966, respectively), which belong to the 16SrII-D group. The sequence was deposited in NCBI as GenBank Accession No. KM359410. A phylogenetic tree using MEGA v5.0 (4) was constructed with 16S rDNA; consensus sequences of phytoplasmas belonging to distinct groups revealed that the present phytoplasma clustered with the 16SrII group. iPhyClassifier software was used to perform sequence comparison and generate a virtual restriction fragment length polymorphism (RFLP) profile (5). On the basis of iPhyClassifier, the 16S rDNA sequence analysis of our isolate showed 99.2% similarity with that of the 'Candidatus Phytoplasma australasiae' reference strain (GenBank Accession No. Y10097), which belongs to 16Sr group II. The virtual RFLP pattern of F2n/R2 fragment was most similar to the 16SrII-D subgroup (similarity coefficient of 0.91) but showed a difference in profile with HpaI, HhaI, and MseI enzymes. Several bacterial/fungal and viral diseases have been reported on A. paniculata (3); however, to our knowledge, this is the first report of witches' broom disease in India and the first record of a 16SrII-D group phytoplasma on Kalmegh. Its presence in Kalmegh is of great significance due to its commercial interest.