Chinese and Swedish researchers have developed a high-yield rice variety that emits up to 70 per cent less methane than normal rice after uncovering how chemicals released by rice roots influence emissions.
The scientists said their new low-methane hybrid rice offered a promising strategy to address a future rise in rice-related emissions because of global warming and an increasing global population.
“We discovered that fumarate and ethanol are two major rice-orchestrated secretions and play a key role in regulating methane emissions,” the team wrote in a paper published in the peer-reviewed journal Molecular Plant on Monday.
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In particular, the team found that rice that produced less fumarate and more ethanol helped reduce methane emissions. Breeding a new rice variety with these characteristics resulted in “70 per cent reductions in methane production”, they said.
Methane is a potent greenhouse gas with a significantly higher heat-trapping capacity than carbon dioxide, although it has a shorter atmospheric lifespan. Emissions originate from various sources, including agriculture and livestock farming, waste decomposition and the energy sector.
The cultivation of rice – a staple food for half the world’s population – alone is responsible for around 12 per cent of man-made global methane emissions, according to a press release by the journal’s publisher Cell Press.
As the global population grows and demand for rice increases, total methane emissions are only expected to rise.
Scientists have known that methane emissions from rice paddies occur when microbes break down organic compounds released by rice roots, although it was not clear which compounds were responsible.
The team, led by scientists from Hunan Agricultural University in Changsha and the Swedish University of Agricultural Sciences in Uppsala, studied a genetically modified low-methane rice they had previously introduced to find the source of emissions.
While the team already had a genetically modified low-methane rice variety, they used traditional breeding methods to create a new hybrid rice with low fumarate and high ethanol.
Genetically modified crops are controversial because of concerns over potential negative health consequences. Studies have indicated that these crops are safe to eat but some countries have banned their cultivation.
China last year pushed to approve a number of genetically modified foods – including wheat, corn and soybeans – in an effort to achieve food security, however it was a long process to achieve this.
To create their hybrid rice, the team crossbred a high-yield variety with a previously screened natural low-methane variety.
When tested in fields across China for several years, the resulting low-methane rice saw an average yield of 8.13 tonnes (8.96 tons) per hectare. The global average for rice last year was 4.27 tonnes (4.71 tons) per hectare, according to the press release.
Anna Schnürer, corresponding author and a microbiologist at the Swedish university, told the journal the team’s research showed that a low-methane and high-yield rice variety could be created “using traditional breeding methods, without GMO, if you know what you’re looking for”.
In the study, the team also treated rice fields with ethanol and oxantel – another compound that they found reduced methane emissions – cutting emissions by 60 per cent without affecting yields.
The researchers hope to register their rice in China to be marketed towards farmers, and are working with companies to see whether oxantel – which is already used as an intestinal worm treatment in humans – could be added to fertilisers.
“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.”
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