Developing rice that can withstand warmer nighttime temperatures has become a key priority for breeders, as research indicates that nights are becoming warmer in the main rice-producing areas. Vibha Srivastava, a plant biotechnology professor in the crop, soil, and environmental sciences department at the University of Arkansas System Division of Agriculture, discusses rice breeding and the promise of gene editing for night heat tolerance in her article titled ‘Beat the heat: Breeding, genomics, and gene editing for high nighttime temperature tolerance in rice,’ featured in the December issue of Current Opinion in Plant Biology.
Rice crops can handle the heat during the day, but they require cooler temperatures when night falls.
Creating rice varieties that can tolerate increased nighttime temperatures is becoming increasingly important as research shows warmer nights in the most significant rice-growing regions.
In the United States, Arkansas yields about half of the nation’s rice, particularly from the Delta region. According to the USDA Economic Research Service, roughly 1.4 million acres of this essential grain, which feeds more than half of the global population, are cultivated in Arkansas.
“Integrating tolerance genes into Arkansas rice has proven to be quite challenging,” stated Vibha Srivastava, a professor of plant biotechnology at the University of Arkansas System Division of Agriculture. “While progress in this area is just beginning, researchers are identifying promising developments.”
However, Srivastava suggests that gene editing might offer an alternative pathway. Unlike genetic modification, which inserts DNA from other organisms, gene editing does not involve such methods.
In the December issue of Current Opinion in Plant Biology, Srivastava delves into the potential of gene editing for enhancing rice’s tolerance to night heat.
Her co-authors on the article include Christian De Guzman, an assistant professor specializing in rice breeding and genetics, and Samual B. Fernandes, an assistant professor focused on agricultural statistics and quantitative genetics, both from the Arkansas Agricultural Experiment Station, a branch of the University of Arkansas System Division of Agriculture.
This marks the first comprehensive review article regarding nighttime heat tolerance in rice, consolidating all available scientific literature on the subject.
According to Srivastava, additional findings have also been published in the B.R. Wells Rice Research Series, including studies by Paul Counce, a professor at the Rice Research and Extension Center, who led efforts to evaluate rice for high nighttime temperature responsiveness, examining its susceptibility and tolerance.
De Guzman, Fernandes, and Srivastava have secured a four-year, $585,650 grant from the U.S. Department of Agriculture to cultivate rice varieties that can endure high nighttime temperatures. The article in Current Opinion in Plant Biology expands upon the information gathered for the grant proposal.
Understanding Night Heat Tolerance
During the flowering and grain-filling stages, rice is particularly vulnerable to elevated nighttime temperatures compared to high daytime temperatures. While the ideal growing temperatures can vary by region, the authors highlight that most rice varieties start to show sensitivity when nighttime temperatures exceed 28 degrees Celsius (82.4 degrees Fahrenheit).
These increased temperatures can lead to a loss in yield and a degradation in grain quality, often seen as “chalkiness” — an undesirable trait that affects milling quality, cooking performance, and taste.
Recent studies indicate that the effects of high nighttime stress could cause yields to plummet by as much as 90 percent, alongside a notable rise in chalkiness.
While the genetic mechanisms behind susceptibility to high nighttime temperatures remain unclear, it is known that elevated respiration rates during these warm nights redirect energy from growth to repair, impacting biomass development.
Challenges Ahead
Currently, there are no modern rice cultivars bred in the U.S. that can endure high nighttime temperatures during their reproductive phase. Nonetheless, an Indian variety named Nagina 22 displays high tolerance to nighttime heat. However, when cultivated in Arkansas, it exhibited some unfavorable characteristics, such as smaller grain size, increased chalkiness, and taller stalks that are more likely to fall, known as lodging.
Nagina 22 has been crossed with modern cultivars to enhance nighttime tolerance, but the relevant genes have not yet been identified. Without knowing the gene identities, gene editing cannot be applied to improve traits in popular cultivars, Srivastava explained. Meanwhile, she points to gene editing as a potential method to enhance desirable traits in Nagina 22 or its hybrids.
Some promising advanced breeding lines in the Arkansas Rice Breeding Program could be suitable candidates for gene editing if they display improved traits related to yield and grain chalkiness after experiencing high nighttime stress.
A vital factor with Nagina 22 and its hybrids will be to reduce its naturally high chalkiness levels. The cloning and analysis of Chak5, a significant chalky DNA region in rice, provide a pathway towards decreasing chalkiness via gene editing, she noted.
“Our aim is to enhance production and improve the flavor of rice, while also ensuring grain quality remains a priority,” Srivastava stated.
Rising Nighttime Temperatures
National and regional analysis indicates a trend of nighttime warming in the U.S. According to the Fifth National Climate Assessment published in 2023, “nighttime temperatures and winter temperatures have risen more rapidly than daytime and summer temperatures.”
