Identification of a strain related to phytoplasma infection in marigold in India

Phytoplasma is a group of extremely small bacteria. They don’t have a cell wall and any particular shape. They are bacterial parasites of plants and insects. Marigold is an important floricultural crop which has been reported as phytoplasma host from many countries like Mexico, India and Hungary. The state of Karnataka is one among the leading producer of Marigold flowers in India. Marigold is the most widely cultivated commercial flower of Karnataka, it has a significant role in the national and international flower trade. Phyllody and associated symptoms of phytoplasma infection have a direct negative impact on the quality and market value of marigold flowers.

Typical disease symptoms on marigold plants, from the left: healthy marigold plant with normal inflorescence, and with virescence and phyllody symptoms.

Researchers conducted field surveys in the marigold growing areas of Karnataka from April 2016 to July 2018 to assess the presence of phytoplasma associated symptoms in the crop. A total of ten symptomatic and two asymptomatic samples were collected and the percentage of disease incidence was determined by taking into account the number of diseased plants for every 100 plants evaluated. DNA extraction was done from the leaves of symptomatic and asymptomatic plants. Characterization of phytoplasma was done using direct and semi-nested PCR assays. The virtual RFLP patterns were generated and compared with the reference phytoplasma strains of different 16Sr groups. The assembled 16Sr sequences and the sequences retrieved from the GenBank were aligned and
a phylogenetic tree was constructed.

The symptoms of phyllody, yellowing, discoloration of florets, stunted growth, purpling and crinkled leaves were observed on marigold plants. The virtual RFLP patterns resulted identical with the one of papaya yellow crinkle phytoplasma, ‘Candidatus Phytoplasma australasia’ classified in the 16SrII group, subgroup D with the similarity coefficient of 1.00. In this study, the symptomatic samples of marigold collected from different fields resulted infected with a ‘Ca. P. australasia’-related strain, which has not been reported in India in this plant species. This study is the first report of 16SrII phytoplasmas associated with marigold phyllody from the Karnataka state.


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