AsianScientist (Jun. 09, 2024) – On June 8, 2023, scientists at the National Oceanic and Atmospheric Administration in the United States officially declared the arrival of El Niño — a signal for governments, farmers and agricultural scientists across the world to brace for a hot year ahead.
In Southeast Asia, April through June is typically the hottest time every year before being quenched by monsoon rains. But in 2023, El Niño brought record high temperatures during the summer months, raising concerns over its impact on food production in the region. For example, the Ministry of Agriculture and Cooperatives in Thailand predicted that rice production could decline by up to six percent for the 2023–24 harvest season in the country. Thailand is one of the major exporters of rice in Asia.
During the previous El Niño event in 2015, 85 percent of the provinces in the Philippines experienced severe drought. By March 2016, an estimated US$ 217 million worth of crops had been destroyed due to heat, according to the Department of Agriculture in the Philippines.
Although many staple crops have evolved to withstand heat, they are often unable to adapt to extreme heat and drought, which leads to lower yields and, sometimes, crop failures.
Aware of the impacts of rising heat in general and events like El Niño in particular on agriculture, scientists in Southeast Asia have been developing heat-resistant crops. They are also advising local policy makers and farmers on the best agricultural practices to ensure that Southeast Asia—home to 8.5 percent of the world’s population—stays fed.
IT’S NOT A MEAL WITHOUT RICE
For many cultures in Southeast Asia, a meal lacking rice is incomplete. It is not surprising then that most of the calories consumed in the region come from this staple—upwards of 75 percent, depending on the country.
However, rice is particularly sensitive to extreme heat. In 2015, the El Niño event caused rice production to drop by 15 million tons in Southeast Asia alone. Globally, this loss contributed to a 16 percent inflation in the price of rice, according to the Food and Agriculture Organisation.
The International Rice Research Institute (IRRI) in the Philippines, with over 600 research and development partners worldwide, has been at the forefront of rice research to develop robust varieties to ensure food security in the region. In a hallmark study published in the Proceedings of the National Academy of Sciences, IRRI reported exactly how sensitive rice crop yield is to heat.
The researchers examined the relationship between temperature trends and rice yields over 24 years in the Philippines and found that for every one degree increase in the minimum temperature during the growing season, rice yield declined by 10 percent.
One notable technique that IRRI has adopted to make heat-resistant rice is genome editing, in which scientists directly modify the plant’s DNA to introduce a desirable trait. Genome editing is also a fast and cost effective technique that can be used to complement conventional breeding.
“With editing, we can directly introduce a particular trait or allele into the popular varieties, mimicking the variation that already exists,” explained Inez Slamet- Loedin, head of Rice Genetic Design and Validation Unit at IRRI, in an interview with Asian Scientist Magazine. “Compared to conventional breeding—which may take several generations of crossing—genome editing takes only one third of the time.”
The next step is to determine which stage of rice development is better for the modification to be introduced. The developmental stages of rice can be roughly divided into three parts: the vegetative stage, which involves germination and early seedling growth; the reproductive phase, which is characterized by increased plant height, booting, heading and flowering; and the ripening phase, which brings the plant to maturity before harvesting. Among these, the reproductive period is the most sensitive to high temperatures. Presently, researchers are targeting this phase for genome editing to make it more heat resistant.
“At the moment, about 97 genes related to heat tolerance have been identified, 23 of which have been cloned,” said Slamet-Loedin, adding that the gene editing studies for heat tolerance are currently ongoing at IRRI.
TESTING GROUNDS
It will take a couple of years for the ongoing studies to bring new, heat-resistant rice strains to the market. In the meantime, B.P. Mallikarjuna Swamy, senior scientist I for Rice Breeding and Biofortification at IRRI, told Asian Scientist Magazine that farmers should pay closer attention to weather predictions from their local meteorological departments and choose their crops accordingly.
For example, he said, farmers can plant heat-tolerant rice varieties that already exist on the market, such as Nagina22 (N22) and adjust their planting time in a way that the heat-susceptible reproductive phase does not coincide with the hottest months of the year. “This would mean either harvesting the crops before the onset of the heat or planting in such a way that the critical stage escapes the heat stress,” said Swamy.
In addition to rice, scientists are studying other types of plants, such as legumes, to improve their heat tolerance. Harsh Nayyar, professor in the Department of Botany at Punjab University in India has successfully identified heat-tolerant genotypes of chickpea, mung bean and urd bean. “These heat-tolerant genotypes have demonstrated enhanced reproductive function stability under heat stress conditions,” said Nayyar in an interview with Asian Scientist Magazine.
Compared to their heat-sensitive counterparts, these genotypes have better chlorophyll retention, reduced oxidative damage and increased nodule formation—all signs of superior cellular function which help them tolerate heat.
Wheat is another major staple crop in Asia that is being studied to enhance its resistance against extreme heat. With every degree increase in temperature, wheat yields decline by about six percent, according to a 2015 study published in Nature Climate Change. Scientists from the Borlaug Institute for South Asia in New Delhi collaborated with the International Maize and Wheat Improvement Center, headquartered in Mexico, to test the robustness of 3,322 new wheat varieties they had developed to warmer temperatures in India. The research team planted these strains earlier in the growing season (October) when temperatures are warmer and found that the best performing strains yielded almost two tons per hectare more than a standard wheat strain. The study was published in Genes in 2021.
Going forward, it’s not just these laboratory-developed varieties that will help reduce the heat strain on agriculture, governments and local municipalities will also need to work together to ensure that farmers have access to resources such as affordable energy and irrigation systems to sustainably grow their crops. Insufficient water supply, for example, can make the impact of extreme heat even worse in a rice field. Similarly, smoother administrative systems will need to be created for efficient government approval of the newly developed heat-resistant varieties so that they can reach the hands of farmers sooner.
“It is very important that when we develop new varieties, we work together with national and local partners so that the product suited to local conditions, reaches the beneficiary faster and meets the local needs,” said Slamet-Loedin.
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This article was first published in the print version of Asian Scientist Magazine, January 2024.Click here to subscribe to Asian Scientist Magazine in print.
Copyright: Asian Scientist Magazine; Image: Ng Yong Wei
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