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Perennial upland rice takes root

Upland rice is a staple for millions of hill farmers in Asia (David Van Tassel)
Upland rice is a staple for millions of hill farmers in Asia
David Van Tassel

On Hainan Island, off the south coast of China, cuttings from a ten-year old rice plant flourish in the plots of an experimental station. In surrounding fields, thousands of its progeny compete for higher yields as they knit the soil with a carpet of roots. A tenth birthday is a surprising achievement for a plant so closely associated with annual cycles of planting and harvesting, but this venerable plant is a rare and successful cross between cultivated rice and a wild perennial relative. Whilst the harvest from the plot is modest, the potential for perennial rice production promises a more secure future for eroded soils across Southeast Asia.

The familiar image of rice cultivation is one of muddy, irrigated paddies in valley bottoms, and yet many millions of farmers, particularly in Southeast Asia, depend on upland rice planted on dry hillsides. However, steep slopes, scarred by deforestation and exploited by poor farmers, are vulnerable to rapid erosion of the fragile topsoil. Such is the problem in the far south of China, where researchers from the Yunnan Academy of Agricultural Sciences are working on a more sustainable future for upland rice farming.

Erosion of slopes is a particular problem with cultivated Asian rice (Oryza sativa), as the crop is harvested and removed every year; between growing seasons, the bare soil remains unprotected. Perennial rice, by contrast, develops underground stems - rhizomes - which remain in the soil and re-grow as soon as the main crop is harvested.

Hybrid solutions to slippery slopes

All domesticated rice is annual, but wild perennial relatives do exist. One such is O. longistaminata, an African wild red rice often perceived as a noxious weed. Efforts to create a hybrid of the two species, with the perennial durability of one parent and the grain production of the other, began at the International Rice Research Institute (IRRI) in the Philippines in 1997.

Peng Xu, a rice breeder at YAAS, has been developing self pollinating hybrid rice plants (David Van Tassel)
Peng Xu, a rice breeder at YAAS, has been developing self pollinating hybrid rice plants
David Van Tassel

Despite early successes, the upland programme ceased its work at IRRI in 2001, although a partner at the Yunnan Academy of Agricultural Sciences (YAAS) continued the work. Dr. Tao Dayun had already managed to bridge the difficult genetic gap between the two species and a single fertile plant was successfully raised in 1999. Continuing under the leadership of deputy-director general for research, Hu Fengyi, progress accelerated in 2007 with funding from The Land Institute in the US, which is known for its breeding of perennial grain crops for temperate areas. Hu has now produced thousands of perennial rice plants by self-pollinating the original hybrid and crossing it with other common cultivated rice varieties.

However, early generations of hybrids produce little, if any, seed: out of a nursery of 6,000 plants, only two perennial individuals were able to produce more than 100 grains of rice. The researchers have used these best yielders for further breeding, but Hu believes it will take another 5-10 years before perennial rice is ready for cultivation on the hills of Southeast Asia. "The Chinese government is interested in introducing perennial rice farming," he reports, "but the research process has raised many unsolved problems and we are still working on a variety ready for farmers to use."

An uphill journey

The challenges are not easy to overcome. The first problem involves a stubborn genetic link between perenniality and seed production: the hybrids producing the most rhizomes underground are most commonly sterile. Therefore the researchers are turning to genetic analysis to learn how to break the connection. The second challenge is a tendency for seed to shatter, which originates from the wild parent. Finally, Hu's team will need to produce plants that can survive in a range of temperatures and rainfall levels beyond the balmy, tropical fields of Hainan and Yunnan.

The underground stem, or rhizome, of perennial rice plants protects the soil from erosion after harvesting (David Van Tassel)
The underground stem, or rhizome, of perennial rice plants protects the soil from erosion after harvesting
David Van Tassel

Although yields remain a concern, and it's unlikely that a harvest of perennial rice will match today's star annuals, perennials allow for two or more harvests in a year and use water and minerals more efficiently, making for competitive production over the longer term. And, with many rice-farming households struggling to meet labour demands, the prospect of developing a variety that does not require annual ploughing, planting and flooding is an attractive one. On the other hand, new approaches will be needed for managing weeds and pests.

Dr. Erik Sacks, who headed up the initial research at IRRI, remains optimistic, observing, "Any time there is a potential solution to a problem in rice production, there will be researchers from various countries interested in taking a closer look. That said, perennial rice is not yet a mainstream concept and a big success will be needed to get a large number of researchers to take notice."

Written by: T. Paul Cox

Date published: July 2009


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