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Herbicide-Tolerant Rice Varieties

  • 28 Sep 2021
  • 5 min read

Why in News

Recently, the Indian Agricultural Research Institute (IARI) has developed the country’s first-ever non-GM (genetically modified) herbicide-tolerant rice varieties (Pusa Basmati 1979 and Pusa Basmati 1985).

  • These varieties can be directly seeded and significantly save water and labour compared to conventional transplanting.
  • ICAR-IARI is a deemed university.

Key Points

  • About the New Varieties of Rice:
    • The new varieties contain a mutated AcetoLactate Synthase (ALS) gene making it possible for farmers to spray Imazethapyr, a broad-spectrum herbicide, to control weeds.
      • The ALS gene in rice codes for an enzyme (protein) that synthesises amino acids for crop growth and development.
      • The herbicide sprayed on normal rice plants binds itself to the ALS enzymes, inhibiting their production of amino acids.
    • Imazethapyr, effective against a range of broadleaf, grassy and sedge weeds, can’t be used on normal paddy, as the chemical does not distinguish between the crop and the invasive plants.
    • However, the new basmati varieties contain a mutated ALS gene whose DNA sequence has been altered using ethyl methanesulfonate, a chemical mutant.
      • As a result, the ALS enzymes no longer have binding sites for Imazethapyr and amino acid synthesis isn’t inhibited.
    • The plants can now “tolerate” application of the herbicide, and hence it kills only the weeds.
    • It is important to note that, as there is no foreign gene involved in the process, the herbicide-tolerance is through mutation breeding. Thus, it is not a Genetically modified organism.
  • Advantages of These Varieties:
    • Direct Seeding of Rice Activity: The new varieties simply replace water with Imazethapyr and there’s no need for nursery, puddling, transplanting and flooding of fields.
      • Water is a natural herbicide that takes care of weeds in the paddy crop’s early-growth period.
      • The new varieties will help in Direct Seeding of Rice (DSR) which has several advantages over paddy transplantation.
    • Cheaper Option: DSR cultivation is currently based on two herbicides, Pendimethalin and Bispyribac-sodium.
      • However, Imazethapyr is cheaper than these two options.
    • Safer Option: Imazethapyr, moreover, has a wider weed-control range and is safer, as the ALS gene isn’t present in humans and mammals.

Paddy Transplantation vs Direct Seeding of Rice

  • Paddy Transplantation:
    • The field where the seedlings are transplanted has to be “puddled” or tilled in standing water.
    • For the first three weeks or so after transplanting, the plants are irrigated almost daily to maintain a water depth of 4-5 cm.
    • Farmers continue giving water every two-three days even for the next four-five weeks when the crop is in tillering (stem development) stage.
    • Paddy transplantation is both labour- and water-intensive.
  • Direct Seeding of Rice (DSR):
    • In DSR, the pre-germinated seeds are directly drilled into the field by a tractor-powered machine.
    • There is no nursery preparation or transplantation involved in this method.
    • Farmers have to only level their land and give one pre-sowing irrigation.
  • Advantages with Direct Seeding of Rice:
    • Water savings.
    • Less numbers of labourers required.
    • Saves labour cost.
    • Reduce methane emissions due to a shorter flooding period and decreased soil disturbance compared to transplanting rice seedlings.
  • Drawbacks of Direct Seeding of Rice:
    • The seed requirement for DSR is also high, 8-10 kg/acre, compared to 4-5 kg/acre in transplanting.
    • Further, laser land levelling is compulsory in DSR. This is not so in transplanting.
    • The sowing needs to be done timely so that the plants have come out properly before the monsoon rains arrive.

Source: IE

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