Heat waves underscore urgency of developing heat-tolerant crops

Southeast Asia grappled with a record-breaking heat wave in April and May that not only claimed hundreds of lives but diminished entire crop harvests, putting the region’s food security in jeopardy. The frequency and intensity of heat waves are only expected to increase in line with climate change. And though plant scientists have for decades bred climate-resilient crops — strengthening their tolerance to drought, flooding, and emerging diseases — experts say not enough is being invested into the research and development of crops that can withstand extreme heat. “There is so much potential but not enough funding,” said Benjamin Kilian, senior scientist and project coordinator at the nonprofit Crop Trust, which works to conserve crop diversity and funds gene banks worldwide. “On the global scale, we need more investments into this work.” The outcry from farmers in places such as Thailand, Vietnam, and Cambodia — where the 50 degrees-Celsius heat destroyed rice, pepper, and fruits — is highlighting the need to accelerate the research into heat-tolerant crops. While tomatoes, cassava, and pearl millet are known to be naturally able to withstand higher temperatures, scientists are looking at whether staple crops such as wheat, barley, and rice could be genetically adapted in the lab to do the same. Higher temperatures limit crops’ reproduction and growth while harming photosynthesis, respiration, and the availability of vital water, be it from rainfall or irrigation systems. All of these factors can make crops more vulnerable to disease. “There is a growing interest in growing heat tolerant crop varieties because of the increasing effect of climate change and heatwaves in irrigated and rainfed environments, which significantly affects crop yield and nutritional quality,” said Wuletaw Tadesse Degu, who leads research on breeding wheat that is resistant to diseases, drought, and heat stressors at the International Center for Agricultural Research in the Dry Areas, or ICARDA. It is headquartered in Lebanon with a sub-Saharan program focused on breeding high-yielding, heat-tolerant wheat varieties. Breeding plants to tolerate other climate stressors — such as salinity, drought, and submergence — has been historically prioritized over heat, according to Amelia Henry, a senior scientist for stress physiology at the Philippines-based International Rice Research Institute. This could be because developing crops’ heat tolerance can be more time-consuming and difficult to research compared to other forms of crop resilience, or because the effects of stressors such as floods and salinity are more visible, she said. At the IRRI, this means that even though researchers are raising internal alarms to escalate heat tolerance as a priority, funders have not followed suit. The organization needs more resources in order to discover wild rice varieties that can naturally withstand heat or whose heat-tolerant genes can be cloned in a modified variety. How heat affects crops But without such investment, some countries’ food security could hang in the balance. For every 1 degree Celsius rise in the global mean temperature, an estimated 6% of global yields of wheat — a staple crop for a third of the global population — could be lost, alongside 3.2% of rice and 7.4% of maize. Together, these three grains supply over half of the global population’s food energy. Rice flowers’ pollen is sensitive to heat, and if it can’t survive then plants can’t form grains for rice, Henry said. Extreme heat can also come with significant economic ramifications. In Thailand, where a reduction in crop yields is estimated to mean a rise in farmers’ debt by 8% this year, heat meant durian fruits ripen faster without reaching their optimal size. Because durians are sold in terms of weight and size, this has diminished the price of Thailand’s third most valuable agricultural product. “This year is a crisis,” Busaba Nakpipat, a durian farmer, told AFP, adding that if higher temperatures continue, farmers won't be able to produce the lucrative fruit anymore. “We have prayed for rain.” Meanwhile, a growing global population means food production will need to increase by an estimated 56% by 2050 in order to feed the projected population, according to a 2018 study by the World Resources Institute. Rising heat could stifle such efforts. Developing climate-resilient crop varieties and deploying them to farmers falls within the broader field of climate adaptation research. As it stands, funding for climate adaptation is limited; it accounted for 36% of total global climate finance in 2021–2022. Only a small portion of that is then allocated to research, said Degu of ICARDA. The genome editing journey But modifying crop genes costs time and money. The process starts with collecting wild varieties of crops from various locations. Wild crops are those that occur naturally — versus those that have been cultivated and intentionally planted to meet human needs. While humans have domesticated wild plants for millennia, that process has narrowed the genetic diversity of the main crops we eat, lowering their potential to adapt to climate change. Should those wild crops be found naturally flourishing in hotter areas, their traits can be identified and used to breed new versions. They must then be tested in both a controlled environment and with farmers in their fields. This process takes a minimum of 12 years — a timeline that may seem long for donors, but to researchers it makes 2050 feel just around the corner. “So we're two breeding cycles away from when we have to double productivity. If you look at the urgency, it's very difficult to say internationally that we're investing enough in this,” said Donald Ort, a professor in plant biology and crop sciences at the University of Illinois. Additionally, the work “is extremely challenging,” and results are not guaranteed, Kilian said. To tackle agricultural diseases only requires the modification of a few genes — but there are over 100 genomes that could contribute to making crops resistant to drought and heat, he explained. But showing it is possible, ICARDA's scientists have developed numerous new crop varieties of wheat, barley, lentils, and fava beans able to withstand extreme temperatures, water scarcity, and emerging pests and diseases — and those seeds have been distributed to governments in Africa, the Middle East, and Asia. For example, scientists have modified lentils’ seed size and shortened the time it takes to grow the crop to better incorporate them into various cropping systems. Fava bean seeds are being developed to withstand higher temperatures during the flowering stage, and malt and fodder barley are being enhanced by combining malting quality in agreement with international industrial standards with disease and lodging resistance and high straw production. “Our strategy at ICARDA is to develop high-yielding, drought tolerant, [and] heat tolerant germplasms with resistance to the major pesticides and disease in the region,” Degu explained. Germplasms refer to seeds, plants, or plant parts that are used in crop breeding. The Germany-based Crop Trust, which is funded by the Norwegian government, is also exploring the breeding of 26 potentially climate-resilient crops, including barley, potato, finger millet, and grass pea. Working on heat tolerance is harder than working on other climate threats, such as salinity or submergence, as those conditions can more easily be emulated for testing, said Henry of the IRRI. “If you want to screen a bunch of breeding lines under heat you’re depending on this extreme heat occurring naturally and that probably only happens once a year and not every year,” she explained. Greenhouses don't emulate the same conditions. This latest heat wave in Southeast Asia allowed the IRRI to do more testing in Thailand and India, Henry said. Meanwhile, colleagues in Japan have already discovered a wild variety of rice that flowers at 6 a.m. versus the typical 9 a.m. which the IRRI is beginning to incorporate into various genetic backgrounds to create new rice varieties. “They’ve progressed that into a modern variety that breeders can use to change the flowering time of their variety,” Henry said. “The reason that’s an advantage under heat is because if flowers open up earlier in the morning before it’s hot out, the pollen is more likely to survive.” Research in progress Elsewhere, researchers are delving into the science behind crop growth to see how more varieties might be genetically altered to improve their chances of survival. In the United States, Ort and his team have been trying to improve photosynthesis — the process of turning light energy into chemical energy — to improve resilience in crops such as soybeans and potatoes. And in the United Kingdom, biologist professor Tracy Lawson is leading a laboratory dedicated to developing climate-resilient plants at the University of Exeter and partly funded by the Wolfson Foundation. It explores how to manipulate the numbers and behavior of pores in crop plants to improve photosynthesis, water use efficiency, and temperature. “We also need to look at combined stress, for example, there might be flooding earlier in a growing season that the crop needs to cope with and then later on temperature becomes a stress,” she said. The Chinese Academy of Sciences has already seen some success in engineering rice and mustard seeds so they can better repair heat damage and produce more grain. In Thailand, initial research on molds, a type of fungi, found heat-tolerant varieties in soil samples from pineapple and sugarcane fields, which can then be built upon to improve fruits’ resilience. And the universities of Yale, California, Berkeley, and Duke alongside China’s Tao Chen Huazhong Agricultural University, have discovered a way of preventing the decline of plants’ defense hormone, which occurs in hotter weather and weakens plants’ defenses to disease. All of this could safeguard crops around the world from higher temperatures. But against the ticking clock of climate change, the calls for more funding are resounding. “In 10 years I’d like to see … farmers growing improved varieties in many regions and they are happy and get more income,” said Kilian, but he’s skeptical that will happen if donors don’t step up.