A study has found out that rice suffering from heat stress is at risk of becoming sterile.
“High temperature stress is one of the most important constraints in rice production in the Philippines,” Norvie L. Manigbas, Chief Science Research Specialist, Philippine Rice Research Institute, said during a webinar presentation of his study on “Rice Improvement for High Temperature Adaptation in the Philippines.”
The event was organized by the Department of Science and Technology-National Research Council of the Philippines (DoST-NRCP).
Information from the DoST showed that rice normally thrives in temperatures between 20 to 35 degrees Celsius, but it becomes increasingly sensitive when the temperature reaches over 35 degrees Ccelsius, especially during the reproductive stage. Based on study, many rice varieties in the farmers’ field are recorded to have high sterility of up to 80 percent, and very few can tolerate heat stress.
Historical data from Philippine Rice Research Institute (PhilRice), since 1998 to 2019, and from DoST-Philippine Atmospheric, Geophysical, and Astronomical Services Administration, since 1971 to 2000, shows that the temperature in local fields has reached the critical level of 35 degrees Celsius or more by which rice can be affected.
If this will continue without mitigation or other measures to at least reduce it, in the year 2065, as projected by DoST-PAGASA and other agrometeorological government agencies, there will be a 2.5 to three degrees Celsius increase in temperature, higher than it is today.
“If high temperature persists, which is predicted to increase by 1.1 to 2.4 degrees Celsius 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 percent in susceptible varieties,” Manigbas said.
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.
High temperature can induce high spikelet sterility among rice which are at flowering stage, and this can result in having more unfilled grains due to heat stress, and in the process, lower rice yields. For instance, if there are 30 unfilled grains in a 100 grain sample, then spikelet sterility is 30 percent. The higher the percentage of spikelet sterility, the lower yield is expected.
The high temperature during the 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 to 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. Once approved, there is a plan to deploy these varieties initially to high temperature areas in the farmers’ field in Tuguegarao City, Cagayan and Pili, Camarines Sur for the 2021 dry season cropping.
DoST-NRCP has been initiating public awareness and discussion on important science and technology issues to enable the public to be more aware of the social science behind the S&T issues.DoST-NRCP’s future webinar announcements and other events can be found in their Facebook page Research Pod.