The Indian Agricultural Research Institute (IARI) has created the country’s first non-GM (genetically modified) herbicide-tolerant rice varieties, which may be planted directly and save water and labour over traditional transplanting.
Farmers may spray Imazethapyr, a broad-spectrum herbicide, on the cultivars Pusa Basmati 1979 and Pusa Basmati 1985 because they have a mutant acetolactate synthase (ALS) gene. This eliminates the need for nurseries, where rice seeds are grown into young plants before being plucked and transplanted in the main field 25-35 days later.
Paddy transplanting requires a lot of time and water. The seedlings must be transplanted onto a field that has been “puddled” or tilled in standing water. The plants are watered nearly daily for the first three weeks or so after transplanting to maintain a water depth of 4-5 cm. When the crop is in the tillering (stem development) stage, farmers continue to water every two to three days for the following four to five weeks.
“Water is a natural pesticide that kills weeds in the early stages of rice crop development. There is no need for a nursery, puddling, transplanting, or flooding of fields with the new kinds since Imazethapyr replaces water. Paddy may be planted directly like wheat, according to A K Singh, director of IARI.
Imazethapyr, which is effective against a variety of broadleaf, grassy, and sedge weeds, can’t be used on regular paddy since the chemical can’t tell the difference between the crop and the invading plants. In rice, the ALS gene codes for an enzyme (protein) that synthesises amino acids for crop development and growth. The herbicide sprayed on normal rice plants binds to the ALS enzymes, preventing amino acid synthesis.
The DNA sequence of the ALS gene in the new basmati cultivars has been changed using ethyl methanesulfonate, a chemical mutation. As a consequence, Imazethapyr no longer binds to the ALS enzymes, and amino acid synthesis is unaffected. Plants may now “tolerate” herbicide treatment, resulting in just weeds being killed.
“Herbicide tolerance is achieved via mutation breeding, not genetic modification.” “There isn’t a single foreign gene here,” Singh said.
Both Pusa Basmati 1979 and 1985 were developed by crossing two popular types, Pusa 1121 and Pusa 1509, with ‘Robin.’ The latter is a mutant line developed from Nagina 22, an upland rice variety that can withstand drought. S Robin, a rice breeder from Tamil Nadu Agricultural University in Coimbatore, discovered the mutant for Imazethapyr tolerance.
In response to labour constraints and decreasing water tables, farmers in Punjab and Haryana are already using direct planting of rice (DSR). DSR has been applied to around 6 lakh of the total 44.3 lakh hectares of rice land in the two states this year.
Pendimethalin (used within 72 hours of planting) and Bispyribac-sodium are the two herbicides presently used in DSR farming (after 18-20 days). “These are more expensive than Imazethapyr (Rs 1,500 vs Rs 300/acre),” Singh said. Furthermore, since the ALS gene is absent in humans and animals, Imazethapyr has a broader weed-control range and is safer. The pesticide will exclusively target the weeds in herbicide-tolerant rice.”
Paddy transplantation usually requires approximately 30 irrigations, each of which consumes about 5 hectare-cm of water (one hectare-cm equals 100,000 litres). Puddling takes up approximately 15 hectare-cm on its own. Overall, DSR is expected to use 30% less water, save Rs 3,000 per acre in labour costs, and save 10-15 days owing to the lack of nursery preparation. However, DSR’s effectiveness is contingent on a viable herbicide solution, like the development of Imazethapyr-tolerant cultivars.
Source: The Indian Express