Revolutionary Weed Control in Rice and Wheat: New Herbicide-Tolerant Varieties

What’s in today’s article?

• Why in News?
• Recent breakthroughs in rice and wheat fields
• Prevailing practices to control weeds
• Herbicide-tolerant solutions
• Conclusion

Why in News?

Agricultural scientists and policymakers have long sought methods to cultivate rice and wheat with reduced water usage and without burning leftover straw or extensive land preparation. 

In this context, the recent breakthroughs are silver lining in rice and wheat production as these involve breeding rice and wheat varieties/hybrids that tolerate the herbicide Imazethapyr, which controls competing weeds.

Recent breakthroughs in rice and wheat fields

• Rice fields
  • In the current kharif season, two basmati rice varieties (Pusa Basmati 1979 and Pusa Basmati 1985) and two non-basmati rice hybrids (Sava 134 and Sava 127) have been commercially planted. 
    • These were developed by the Indian Agricultural Research Institute (IARI) and Savannah Seeds Pvt. Ltd.
  • These contain a mutated acetolactate synthase (ALS) gene that enables farmers to spray Imazethapyr for controlling weeds in rice.
    • Common weeds affecting rice cultivation are: Echinochloa colona (commonly called jangli chawal), Cyperus rotundus (motha) and Trianthema portulacastrum (patthar-chatta).
• Wheat Fields
  • In the upcoming rabi season, Mahyco Pvt. Ltd plans to launch Imazethapyr-tolerant wheat varieties, Goal and Mukut.
    • Imazethapyr is used for controlling Phalaris minor (gulli danda), Chenopodium album (bathua) and other such major weeds.
  • Mahyco and Savannah Seeds have partnered to promote their 'FullPage' direct seeded rice (DSR) and 'FreeHit' zero-tillage (ZT) wheat technologies, aiming to make farming more climate-smart and sustainable.

Prevailing practices to control weeds

• Farmers traditionally control weeds in rice and wheat fields through intensive water use and ploughing.
• For rice
  • Farmers create nurseries to grow young plants, which are transplanted after 30 days into puddled fields. 
  • These fields are kept flooded for the first 2-3 weeks to prevent weed growth and then irrigated weekly for the remainder of the 155-160 day growing season. 
  • This method requires up to 30 irrigations per acre, each using over 200,000 liters of water, plus significant labor costs for transplanting.
• For Wheat
  • Farmers burn the leftover paddy straw and plough the field multiple times to manage weeds. 
  • This involves initial ploughing with a harrow or cultivator, followed by irrigation, and additional ploughing with either a rotavator or harrow/cultivator before sowing wheat seeds.

Herbicide-tolerant solutions

• Solutions
  • Direct Seeded Rice (DSR) and Zero-Tillage (ZT) wheat technologies replace traditional water-intensive and ploughing methods with the herbicide Imazethapyr for weed control.
  • Direct Seeded Rice (DSR)
  • DSR eliminates the need for paddy nurseries, puddling, transplanting, and flooding, allowing paddy seeds to be sown directly like wheat. 
  • The land only requires laser leveling before sowing, costing about Rs 1,200/acre. This method saves around 30% of water and reduces labor and fuel costs.
• Zero-Tillage (ZT) wheat technologies
  • The ‘FreeHit’ ZT technology for wheat, developed by Mahyco, allows direct sowing without burning paddy stubble or land preparation. 
  • Farmers can use a tractor-mounted Super Seeder with rotavator to cut and mix standing stubble into the soil or a Happy Seeder to cut and leave crop residue on the field. This no-tillage approach saves cost and time. 
  • Imazethapyr, along with Metribuzin, is sprayed when the wheat crop is about 25 days old for effective weed management.

Are these solutions genetically modified (GM) crops?

• No, they just have an acetolactate synthase (ALS)that has undergone mutation. This gene is already present in rice and wheat.
  • These are not introduced from soil bacteria or other unrelated species, as with Monsanto’s ‘Bollgard’ Bt cotton and the still-to-be-approved GM hybrid mustard bred by scientists at Delhi University’s Centre for Genetic Manipulation of Crop Plants.
• This gene codes for an enzyme crucial for synthesizing essential amino acids needed for plant growth. 
  • Normally, the herbicide Imazethapyr binds to these ALS enzymes, inhibiting amino acid production and killing both the crop and weeds.
  • However, the mutated ALS gene in these new varieties has an altered DNA sequence, preventing Imazethapyr from binding to the enzyme. 
  • This mutation allows the plants to tolerate the herbicide, which then only targets and kills the weeds.
• This differs from genetically modified crops like Monsanto’s ‘Bollgard’ Bt cotton, as the mutation is achieved through chemical or radiation methods, not by introducing genes from unrelated species.

Conclusion

The adoption of Direct Seeded Rice (DSR) and Zero-Tillage (ZT) technologies, which offer benefits like reduced water and fuel consumption and the elimination of environmental pollution from crop residue burning, is likely to improve with herbicide-tolerant varieties. Additionally, the fact that these crops are not genetically modified (GM) may further facilitate their acceptance.

Q.1. What is Zero-Tillage (ZT) technology?

Zero-Tillage (ZT) technology involves planting crops without disturbing the soil through plowing or tilling. This method minimizes soil erosion, preserves moisture, and enhances soil health by leaving crop residues on the field. It reduces fuel and labor costs, and can improve yields and environmental sustainability.

Q.2. What are genetically modified (GM) crops?

Genetically modified (GM) crops are plants whose DNA has been altered through genetic engineering to enhance desirable traits, such as pest resistance, herbicide tolerance, or improved nutritional content. These modifications are designed to increase agricultural efficiency, reduce losses, and address specific challenges in crop production.

Source: How a new tech promises to kill weeds in rice and wheat fields, remove need for stubble-burning