In the subtropical Yunnan Province of China, high-yielding perennial rice has been successfully developed. In 2021, perennial rice was grown on 15,333 ha by 44,752 smallholder farmers in southern China and is now expanding throughout SE Asia and Africa.
PR23 and a number of other selections were developed through a wide hybrid cross between annual, cultivated rice, Oryza sativa, and a perennial cousin of rice from Africa, Oryza longistaminata. This wide hybridization approach is the same one being employed by breeders at The Land Institute to perennialize sorghum and wheat.
Why Perennial Rice?
- Rice feeds 4 billion people and is the grain most consumed by humans. It’s the third largest cereal grain crop after corn and wheat worldwide in metric tons.
- Rice production is a very labor-intensive activity for farmers, and perennial rice would greatly reduce these labor inputs. 2022 research shows that farmers used nearly 60% less labor and spent almost 50% less on seed, fertilizer, and other inputs for perennial rice than annual rice.
- High-yielding perennial rice produced grain for eight consecutive harvests over four years from a single planting, with average perennial rice yields equivalent to annual rice, with 6.8 Mg ha-1 harvest-1 of perennial rice versus 6.7 Mg ha-1 harvest-1 of replanted annual rice for each perennial rice regrowth cycle.
- By switching from annual to perennial rice, soils accumulated almost a ton of organic carbon per hectare per year, 0.81 Mg organic carbon ha-1 yr-1
- Farmer profits from perennial rice ranged from 17% to 161% above annual rice
Important initial work on perennializing rice took place in the early 1990s when Dr. Tao Dayun of the Yunnan Academy of Agricultural Sciences along with Prapa Sripichitt of Kasetsart University in Bangkok, Thailand successfully produced a single hybrid plant from cross pollinating Oryza sativa and O. longistaminata. In 1995, Dr. Erik Sacks took the helm of a new perennial rice breeding program at the International Rice Research Institute (IRRI) in the Philippines. Sacks used Dayun and Sripichitt’s hybrid plant to develop a breeding population.
Considerable progress was made under Sack’s supervision over the next six years, during which time a Masters student from China named Fengyi Hu joined his lab to work on perennial rice. Unfortunately, IRRI terminated the project in 2001, due to budget cuts. Dr. Sacks returned to the U.S. and gained a faculty appointment at the University of Illinois in Urbana-Champaign while Fengyi Hu returned to Beijing, China to pursue his Ph.D. For about six years the perennial rice breeding program was suspended, but after completing his Ph.D., Dr. Hu took a position at the Yunnan Academy of Agricultural Sciences where he and his team used the existing perennial hybrid rice to conduct important research on rhizomes and the genetic basis of perennialism.
In 2007, Erik Sacks informed Land Institute researchers of the perennial rice project and of Dr. Hu’s research. Inspired by the potential for a perennial rice to address the devastating soil erosion that plagues upland rice fields throughout Southeast Asia, The Land Institute provided start-up funds for Fengyi Hu to reactivate the perennial rice breeding program, and has continued to support Dr. Hu’s work both financially and with expertise. Every year since 2008, two or three researchers from The Land Institute have joined a highly dedicated international group of researchers who visit Dr. Hu’s team in the Yunnan Province to monitor progress and offer advice and encouragement. Today, perennial rice research continues to expand under the supervision of Dr. Hu, who is now Dean of Agriculture at Yunnan University in Kunming.
In the last five years, perennial rice went from 0 to 7000 hectares planted. The majority of this land is in the Yunnan Province of China where the crop was developed, but successful test fields have also been established in Laos, Cambodia, Myanmar, and Vietnam. Trials of perennial rice hybrids from Yunnan have even out-performed annual varieties in Uganda.
Today, it is being grown in nearly a dozen provinces of China. Yields of the perennial rice were similar to those of locally adapted annual varieties. Annual yields in Yunnan have averaged 15 tons per hectare per year (~13,300 lbs per acre). Some perennial rice fields have persisted, flowered, and regrown 6 times (2 harvests per year for 3 years).
- Now that genes for perenniality have been successfully introduced into a general-purpose, high-yielding annual rice using classical breeding techniques, Dr. Hu’s group is making crosses to introduce these genes into other kinds of rice with different ecological and culinary traits. Marker assisted selection accelerates the introgression of these genes into specialized rice backgrounds, including upland rice that can tolerate dry, aerobic, erosion-prone soils. Perennial lowland or paddy rice is primarily being adopted by farmers because it reduces labor requirements. Annual rice is still largely transplanted by hand which is arduous work. Moreover, the rural labor sector has been reduced as younger people move to live and work in urban areas.
- In addition to reducing labor requirements, perennial paddy rice may deliver significant environmental benefits such as soil carbon sequestration and greater nitrogen uptake efficiency. A large question that remains is how the greenhouse gas emissions of methane and nitrous oxide in perennial rice paddies compare with annual rice paddies. Hu’s group is embarking on a long-term experiment to study these and other environmental questions.
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