New Microbe Identified as Cause of Sesame Disease in West Bengal

Researchers have identified a new microbe responsible for a mysterious disease affecting sesame crops in Midnapore, West Bengal. The disease causes sesame plants, after reaching their flowering and fruiting stages, to revert to a vegetative state. White flowers with pinkish tinges turn green, severely impacting the crop’s health and yield.

Sesame, often referred to as the “Queen of Oil,” is one of the oldest oilseed crops, with traces found at ancient Harappa and Mohenjodaro sites. Known for its medicinal benefits, including antioxidants and heart-healthy properties, sesame oil is underutilized as a primary edible oil. To improve sesame’s potential, Indian varieties have been undergoing research for genetic enhancement, led by Prof. Gaurab Gangopadhyay of the Department of Biological Sciences at Bose Institute, Kolkata. His team has successfully developed several improved sesame varieties through molecular marker-assisted breeding over the last 14 years.

However, in recent years, Prof. Gangopadhyay’s team observed a troubling trend in sesame fields across East and West Midnapore. After reaching the flowering stage, sesame plants exhibited a strange reversal to a vegetative state, with flowers turning green and malformed. After investigating the issue, the researchers identified a new microbe as the cause: Candidatus Phytoplasma, a type of Mollicutes bacteria.

This bacterium, which lacks a cell wall, thrives in the nutrient-rich phloem and sieve cells of plants. It is transmitted primarily through phloem-feeding insects, such as leafhoppers, plant-hoppers, and psyllids. These insects are known vectors of Phytoplasma, which infects several commercially important crops like tobacco, maize, and grapevines. In sesame, the disease leads to disfigured flowers and a leafy appearance, known as virescence.

The study, recently published in the Plant Molecular Biology Reporter in 2024, investigates how this bacterium affects the metabolic pathways in sesame, leading to the development of these symptoms. With limited prior knowledge about Phytoplasma’s impact on sesame, this research provides a comprehensive understanding of how the disease develops and affects the plant on a molecular level. This new discovery could aid in developing better management strategies for sesame cultivation and enhance our understanding of plant-microbe interactions.