Think about methane and cows and lambs likely spring to mind. Or perhaps landfill. But rice cultivation is responsible for around 12% of global methane emissions. What’s more, these emissions are expected to increase with global warming and as the human population grows.
The hunt for low-methane rice is therefore heating up. “[…] you can have low methane and still have a rice with high yields,” explained Anna Schnürer, a microbiologist at the Swedish University of Agricultural Sciences. “And you can do it using traditional breeding methods, without GMO, if you know what you’re looking for.”
Schnürer and her team have identified chemical compounds released by rice roots that determine how much methane the plants emit. The information led them to breed a new strain of rice that emits up to 70% less methane, offering “great possibilities for effective mitigation of the global climatic impact of rice cultivation”, they wrote in the journal Molecular Plant.
“It was almost like having a riddle,” said Schnürer. “We noticed that the soil itself contained something that reduced methane emissions, so we started thinking that there must be an inhibitor of some kind that is also causing the difference between the varieties.”
When they re-analysed the root exudates, the team noticed that SUSIBA2 plants, a low-methane emitting GMO variety, also release significantly more ethanol. Adding ethanol to the soil surrounding rice plants reduced methane emissions. The other root exudate they investigated, fumarate, was found to support the micro-organisms (called methanogens) that produce methane.
Using traditional breeding methods (rather than genetic modification) the researchers crossbred a high yield or so-called ‘elite’ rice variety with a previously identified low-methane-emitting variety (the Heijing cultivar) whose root exudate was low in fumarate and high in ethanol. The rice plants from this crossbreeding consistently released root exudates with low fumarate and high ethanol (LFHE) profiles.
When the researchers grew these LFHE rice varieties at various field sites throughout China, they showed that the LFHE rice produced 70% less methane on average compared with the elite variety from which it was bred. The LFHE crops also produced relatively high yields: 8.96 tonnes/hectare on average, compared to the 2024 global average of 4.71 tonnes/hectare. A two-year field trial at two different sites in China showed a 60% reduction in methane emissions without impacting crop yield.
The researchers are working to register the LFHE rice as a variety with the Chinese government and others, meaning that it could be marketed to farmers in the future.
“To make these things happen, we’ll also need some encouragement from governments to motivate and support farmers to use these low-methane varieties,” Schnürer said. “It’s one thing to breed eco-friendly rice varieties, but then it’s critical to get them on the market and to get the farmers to accept them.”
