Transforming Agriculture, Perennially

Perennial Rice

In the subtropical Yunnan Province of China, a perennial rice cultivar called PR23 has been successfully developed and was released in fall 2018 to farmers in China.

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?

  • As a cereal grain, rice is the most widely consumed staple food for a large part of the world’s human population, and it provides more than one-fifth of the calories consumed worldwide.
  • Rice production is a very labor-intensive activity for farmers, and perennial rice would greatly reduce these labor inputs.
  • It is a common practice for growers to cultivate their rice in steep hillside terraces. These terraces reduce erosion but are vulnerable to natural disasters or inadequate maintenance. Year-round perennial rice root systems holding soil in place would further stabilize these slopes.
  • Reducing the frequency of tillage could allow soil structure to recover, improving the water-holding capacity, microbial community and rooting depth of rice fields.

Research History

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).

Research Goals

  • 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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