Description of a novel taxon associated with Sugarcane Grassy Shoot (SCGS) disease

Phytoplasma is a group of extremely small bacteria (mollicutes). They don’t have a cell wall and any particular shape (pleomorphic). Phytoplasma was first identified by a Japanese scientist Yoji Doi as ‘mycoplasma-like-organisms’ in 1967. They are bacterial parasites of plants and insects. Phytoplasmas reside in plant’s phloem tissue while insects serve as vectors for the transmission of infection from plant to plant. Once disease caused by phytoplasma is established, entire fields of crops might be wiped out. Sugarcane is the world’s fourth largest and commercially important crop. Sugarcane Grassy Shoot disease is related to Rice Yellow Dwarf (RYD) phytoplasma which occurs in sugarcane growing countries throughout the world.

The major characteristic of SCGS disease are stunting, profuse tillering, side shoots, chlorotic stripes and bleached white leaf blades. The common symptoms of SCGS in sugarcane plant are narrowing and partially or almost chlorotic leaf lamina, excessive tillering and witches’ broom symptoms. Severely infected younger plants appear yellowish. The phytoplasma infection often leads to stunted growth, reduction in leaf size, and excessive proliferation of shoots.

Complete leaf chlorosis in SCGS disease &
Grassy appearance of phytoplasma-infected sugarcane plant

It’s important to study the genome of phytoplasma to understand how this tiny microbe causes infection in plants and gets transmitted through insect vectors. Phytoplasma DNA is difficult to isolate and then sequence it further, as researchers have not yet been active in this organism’s laboratory cultivation. Recently, the researchers at NCMR Pune successfully isolated and sequenced sugarcane phytoplasma. In this study, researchers demonstrated the phylogenetic position of 16SrXI-B group phytoplasmas by characterizing the phytoplasma strain associated with Sugarcane Grassy Shoot (SCGS) disease based on comparative genome features and phylogenetic analyses with its closely related phytoplasma taxa and proposed a novel ‘Ca. Phytoplasma’ taxon. This study is the first description of phytoplasma from India and the first description of phytoplasma species based on genome sequences.

Reference: https://pubmed.ncbi.nlm.nih.gov/33289626/

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