Heat-stressed Rice at Risk of Becoming Sterile

Media Release:

THE commonly grown rice varieties in the Philippines have high yields, good grain quality, and resistance to pests and diseases. However, they lack high temperature tolerance.

To fight climate change, breeding for heat-tolerant varieties should be one of the government’s priorities.

Rice normally thrives in temperatures between 20-35° Centigrade, but it becomes increasingly sensitive when the temperature reaches over 35°C, especially during reproductive stage. Based on study, many rice varieties in the farmers’ field recorded to have high sterility of up to 80%, and very few can tolerate heat stress.

Adoption of high temperature-tolerant cultivars very vital

Historical data from Philippine Rice Research Institute (PhilRice), since 1998-2019, and from DOST-PAGASA, since 1971-2000, shows that the temperature in the local fields has already reached a critical level at 35°C or more, by which rice can be affected. If this will continue without mitigation or other measures to at least reduce it, then in the year 2065, as projected by DOST-PAGASA and other agro-meteorological government agencies, there will be a 2.5-3.0°C increase in temperature, or even higher than it is today.

“High temperature stress is one of the most important constraints in rice production in the Philippines,” Norvie L. Manigbas, chief science research specialist, PhilRice, said during a webinar presentation of his study on “Rice Improvement for High Temperature Adaptation in the Philippines”. The Department of Science and Technology-National Research Council of the Philippines (DOST-NRCP) organized the event.

“If high temperature persists, which is predicted to increase by 1.1-2.4°C in the coming decades, future rice varieties should have the tolerance trait. Reports say that heat stress can cause yield decline of up to 14% in susceptible varieties,” Manigbas added.

The adoption of high temperature-tolerant cultivars is one of the most effective countermeasures to maintain high productivity and stability of rice under the anticipated climate in temperate regions. Without rice improvement, old and current rice varieties with no tolerance to heat stress will suffer yield decline.

Heat stressed rice may become sterile

High temperature can induce high spikelet sterility among rice which are at flowering stage, and this can result to having more unfilled grains due to heat stress, and in the process, lower rice yields. For instance, if there are 30 unfilled grains in 100 grain sample, then spikelet sterility is 30%. The higher the percentage of spikelet sterility, the lower yield is expected.

Heat-tolerant rice under DA evaluation

The high temperature during reproductive stage of the rice crop can also cause chalkiness in the grains. When grains are chalky, there will be more grains that are broken during milling and this leads to low milling recovery, low quality of the grains, and lower price.

“I think the government should prioritize strengthening the R&D programs not only for high temperature, but also for multi-trait abiotic stress rice improvement like drought, salinity, and submergence,” Manigbas explained.

There are 312 released rice varieties from 1990-2019 in the Philippines, and there will be 15 more new varieties to be released this 2020.

The new heat-tolerant rice varieties are still being evaluated by the Department of Agriculture (DA). Once approved, there is a plan to deploy the said variety initially to high temperature areas in the farmers’ field in Tuguegarao, Cagayan, and Pili, Camarines Sur, for the 2021 dry season cropping.

The webinar on Rice Improvement is organized by DOST-NRCP, a council of DOST, which has been initiating public awareness and discussion on important S&T issues, so the public will be more aware of the social science behind the S&T issues. Those interested about the DOST-NRCP’s future webinar announcements and other events, they may visit its Facebook page Research Pod. (Geraldine Bulaon-Ducusin, S&T Media Service) — (✓)

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Featured image a Filipino rice farmer credit to Official Gazette of the Philippines.

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