Rice yield to decline as temperatures rise

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    Rice breeders are in a race against time and climate.

    Filipino rice scientists are developing high-yielding varieties that can tolerate a rise in temperature anywhere from 2.5 degrees Celsius to 3° C or even higher than it is today.

    The temperature rise is traced mostly to the increased levels of carbon dioxide (CO2) in the atmosphere.

    CO2 levels hit a new record of 410.5 parts per million (ppm) in 2019 and are expected to keep rising this year, the World Meteorological Organization said in its annual Greenhouse Gas Bulletin on Monday.

    Breaching the global threshold of 410 ppm in just four years – from 400 ppm in 2015 – has never been seen in its records.

    “High temperature stress is one of the most important constraints in rice production in the Philippines,” said Dr. Norvie Manigbas, chief science research specialist at the Philippine Rice Research Institute (PhilRice).

    Local rice varieties now grown by farmers have high yields and good grain quality, and are resistant to pests and diseases, he said during a forum hosted by the National Research Council of the Philippines, Department of Science and Technology.

    However, these varieties lack tolerance to high temperatures brought about by climate change. For this reason, breeding for heat-tolerant varieties is high on the list of research priorities, said Manigbas who heads the Plant Breeding and Biotechnology Division of PhilRice.

    Rice grows in temperatures between 20 degrees Celsius to 35° C. Beyond that, especially during the reproductive stage, rice is increasingly sensitive to high temperature, said Manigbas who presented findings of his study, “Rice Improvement for High Temperature Adaptation in the Philippines”.

    The study found that very few local varieties are tolerant of heat stress; in fact, high temperatures have led to sterility of up to 80 percent.

    Temperature in rice fields have reached the critical level of 35° C, said Manigbas, citing historical data from 1998-2019 at PhilRice and from 1971 to 2000 at the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).