Straight head Disease in Paddy

Why in news?

Research published in Proceedings of the National Academy of Sciences recently has warned the microbial link between arsenic in soil, lower rice yield.

• It is a physiological disorder in rice that causes empty, sterile florets and distorted husks, giving the panicle an erect, "straight" appearance.
• Causes – It is caused by arsenic toxicity, often from arsenic-based herbicides on crops like cotton or naturally occurring high-arsenic soils, soil microbes, etc.

Arsenic (As) is a naturally occurring, semi-metallic element, known for its high toxicity, especially in its inorganic form.

• 1^st reported – In 1912 in USA, subsequently reported in Europe, China, India (West Bengal) and Bangladesh, etc. (Now - recognised as a global threat).
• Symptoms –
  • Sterile florets and distorted palea and lemma (husk) which looks like crescent or “parrot breaking”.
  • The panicles remain upright at maturity because there is no seeds with no weight, (that is why the disease is called “straighthead”).
  • During the vegetative stage, plants may appear darker green and unusually vigorous, but the symptoms are not visible until heading time.
• Impact – The condition can reduce grain yield by up to 70% in severely affected areas.
• It occurs even when the total arsenic level in the soil is relatively low because the real problem is arsenic speciation, (i.e.) the chemical form arsenic takes in the soil and plant.
• Control measures – Through water management (like draining fields), using arsenic-resistant rice varieties, silicon fertilization (to reduce the plant's uptake of arsenic), crop rotation strategies can help mitigate the risk.

India’s status

• World’s 2^nd largest producer and consumer of rice, with 45 million hectares under cultivation.
• High-risk states – West Bengal, Bihar, Assam, and Uttar Pradesh, where groundwater arsenic exceeds 05 mg/L (WHO limit – 0.01 mg/L).
• At present, the Food Safety and Standards Authority of India (FSSAI) does not have a specific standard for arsenic in rice; thus, Indian rice is governed by more generic food safety rules.

Quick Fact

References

1. The Hindu | Microbial link between arsenic in soil
2. National Library of Medicine | Straighthead Disease