Perennial rice are varieties of long-lived rice

Rice

Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...

 that are capable of regrowing season after season without reseeding; they are being developed by plant geneticists at several institutions. Although these varieties are genetically distinct and will be adapted for different climates and cropping systems, their lifespan is so different from other kinds of rice that they are collectively called perennial rice. Perennial rice—like many other Perennial plant

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

s—can spread by horizontal stems below or just above the surface of the soil but they also reproduce sexually

Sexual reproduction

Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...

 by producing flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s, pollen

Pollen

Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 and seed

Seed

A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...

s. As with any other grain crop, it is the seeds that are harvested and eaten by humans.

Perennial rice is one of several perennial grain

Perennial grain

While many fruit, nut and forage crops are long-lived perennial plants, all major grain crops are annuals or short-lived perennials grown as annuals. Scientists from several nations have argued that perennial versions of today's grain crops could be developed and that these perennial grains could...

s that have been proposed, researched or are being developed
, including perennial wheat

Wheat

Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...

, sunflower

Perennial sunflower

Perennial sunflower is a new crop being developed by crossing wild perennial and domestic annual sunflower species.Annual sunflower is a major oilseed crop. Genes from wild perennial relatives may increase root depth and mass and extend the growing season...

, and sorghum

Sorghum

Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...

. Agronomists have argued that increasing the amount of agricultural landscapes covered at any given time with perennial crops is an excellent way to stabilize and improve the soil, and provide wildlife habitat.

Perennial rice breeding was initiated at the International Rice Research Institute

International Rice Research Institute

The International Rice Research Institute is an international NGO. Its headquarters are in Los Baños, Laguna, Philippines, and it has offices in sixteen countries...

, Philippines and are currently being developed at the Yunnan Academy of Agricultural Sciences, People's Republic of China, and other institutions, but are not yet available for distribution.

Perennial and annual rice

Domesticated Asian rice, Oryza sativa

Oryza sativa

Oryza sativa, commonly known as Asian rice, is the plant species most commonly referred to in English as rice. Oryza sativa is the cereal with the smallest genome, consisting of just 430Mb across 12 chromosomes...

is a short-lived plant. Most cultivars die after it producing seeds, though some can regrow (ratoon) and produce a second crop under favorable conditions. In regions with mild climates, two or three crops of rice may be grown each year. Except for ratoon crops, this means that the dead stalks must be removed, the soil cultivated, and new seed sown every few months.

In contrast, the wild ancestor of Asian rice, Oryza rufipogon, often lives for many years, setting seed each year and spreading vegetatively. In addition to these perennial

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

 types, someOryza rufipogon populations are annuals

Annual plant

An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...

 or intermediate in lifespan

Other wild species in the genus Oryza

Oryza

Oryza is a genus of seven to twenty species of grasses in the tribe Oryzeae, within the subfamily Bambusoideae, native to tropical and subtropical regions of Asia, Northern Australia and Africa...

are also perennial. While perennial Oryza rufipogon

Oryza rufipogon

Oryza rufipogon, known as brownbeard rice and red rice is a member of the genus Oryza. It has a close evolutionary relation to Oryza sativa, the rice grown as a major food crop throughout the world. O...

spreads vegetatively by above-ground stems (stolon

Stolon

In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...

s), Oryza longistaminata

Oryza longistaminata

Oryza longistaminata A. Chev. & Röhr, can be found in the USA where it is regarded as a noxious weed, and in the Nylsvley Nature Reserve in South Africa...

, O. officinalis, O. australiensis, O. rhizomatious spread by underground stems (rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s).

Rice is an important world crop

Rice is most economically important crop in the world according to the Food and Agriculture Organization of the United Nations database. Rice is the number one cereal

Cereal

Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...

 in the human diet, supplying humanity with 23% of its calories. Slightly more maize

Maize

Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 is produced globally (791 vs. 659 million tonnes in 2007), but while 40-80% (61% average) of maize is fed to animals, less than one percent of rice is used as animal feed.

Perennial plants can reduce soil erosion

Farm fields, especially those in the humid tropics

Tropics

The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

, that have been cleared of vegetation or recently plowed are highly vulnerable to soil and nutrient loss through wind or water erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

, soil compaction

Soil compaction

In Geotechnical engineering, soil compaction is the process in which a stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water being displaced from between the soil grains then...

, and decline in soil organic matter

Soil organic matter

Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...

 and microbial biomass

Soil life

Soil life or soil biota is a collective term for all the organisms living within the soil.-Overview:In balanced soil, plants grow in an active and steady environment. The mineral content of the soil and its heartiful structure are important for their well-being, but it is the life in the earth that...

.

Eroded fields become less productive and the soil particles and dissolved nutrients cause environmental problems downstream, including hypoxia

Hypoxia (environmental)

Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...

 in oceans and rivers and the silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

ing of reservoirs and waterways.

Perennial plants regrow quickly after being harvested, re-establishing a protective cover. The fields do not need to be plowed after the initial planting.

Researchers at The International Rice Research Institute (IRRI) believed that perennial rice would "improve the sustainability of food production in the hilly uplands and downstream."

Perennial rice could reduce the rate of deforestation

A high-yielding, nutritious, perennial cereal could allow poor farmers around the world to produce food on a plot of land indefinitely. Currently, many subsistence farmers clear plots in the forest for their crops. Once the soil and/or its nutrients have washed away, the plot is abandoned and a new piece of forest is slashed and burned. Forest may eventually regenerate on the abandoned plot, or weedy grasses may dominate. Environmental impacts of this cropping system include loss of biodiversity, carbon dioxide emissions, increased runoff and decreased rainfall. Deforestation could be reduced by practices that conserve soil productivity

Other potential benefits of perennial crops

• Drought resistance: Annual rice has a shallow root system and is very drought susceptible. A long-lived plant has time to develop a deep and extensive root system making it theoretically capable of accessing more moisture than an annual plant. Tilled soil dries out more quickly than untilled
• Resist weed invasion: Weed pressure has increased in upland rice systems as the fallow period has shortened. Ecologist Jack Ewel wrote: "Weeds are widely recognized as a major impediment to continuous cropping in the humid tropics, and fields are often abandoned more because uncontrollable weed populations are anticipated than because of declining fertility or pest buildups." Grassland restoration with perennials results in fewer annual weeds and perennial grasses, sown at appropriate densities, can out-compete even perennial weeds once they are established.
• Plant nutrition: While shallow rooted species, such as rice obtain most of their nutrients from the topsoil, deep rooted perennials can obtain significant proportion of their phosphorus from the subsoil. "Deep roots are especially important in nutrient-poor substrates because they increase the volume of soil exploited by the vegetation".

Upland rice

Upland rice

Upland rice

Upland rice is rice grown on dry soil. Most rice is grown in flooded rice paddies.- Introduction :Nearly 100 million people now depend on upland rice as their daily staple food. Almost two-thirds of the upland rice area is in Asia...

 is grown on more than 7500000 acres (30,351.5 km²) in the highlands of southern China and across southeast Asia. Because it is grown on steeply sloping soil without terracing, severe erosion results, and a given patch of land can produce rice for only a year or two before it is allowed to return to natural vegetation—only to be cleared and re-sown to rice a few years later. Population increase and agricultural intensification is reducing the fallow period. This is a potent recipe for soil degradation. Were rice a perennial rather than an annual species, its continuously living roots and thick cover of vegetation would prevent such erosion, just as a planting of grass can prevent a roadside slope from washing away. Perennial rice could produce critically needed food year after year on the same plot of land without degrading the soil.

Rainfed paddy rice

38 million ha (26%) of rice lands are terraced but unirrigated. This cropping system produces about 17% of world rice.

While upland rice production systems were the initial target for the perennialization of rice, the perennial habit may prove to have benefits in paddy systems where erosion is less of a concern. Faced with drought one year and flooding the next, "...the rainfed rice farmer can usefully be thought of first as a manager of risk and uncertainty." Given the erratic moisture, many farmers do not use purchased fertilizers. With deforestation, manure may be used as cooking fuel making fertility a key problem. Where fertilizers are purchased, flooding can result in fertilizer runoff contaminating water systems.

Rice with deeper roots, as would be predicted with perennial rice, could exploit the moisture and nutrients in a greater soil volume than short-rooted types (discussed above). The perennial habit could reduce the uncertainty of planting and transplanting with erratic rainfall patterns. Rhizomes would simply lie dormant until temperature and moisture conditions were adequate for emergence.

Irrigated paddy rice

Irrigated rice is very productive and this production method must be fairly sustainable, as it has been practiced in China for millennia however, high yielding rhizomatous rice varieties may still have some advantages, according to Dr. Dayun Tao

• Fixing hybrid vigor: The first generation hybrids between two particular lines or individuals may be exceptionally good, but may be almost impossible to re-create. If the exceptional individual was perennial and rhizomatous, millions of genetically identical plants (clones) could be made from pieces of the rhizomes.
• Expediting the production of inbred lines: Even if the final propagule for the farmers' fields is hybrid seed, not hybrid clones, the parents of exceptional F1 hybrids could be immediately clonally propagated if they were rhizomatous. These genetic replicas could be maintained indefinitely and crossed afresh each year to produce new F1 hybrid seed. Normally, re-creating parents using sexual reproduction requires many generations of inbreeding.
• Ratoon cropping: In some environments, additional grain crops could be harvested each year if the plants ratooned quickly. Shoots growing from the mature plant can reach the reproductive stage more quickly than shoots growing from seed. Transplanting seedlings is faster than sowing seed, but still requires time and labor intensive field preparation and, of course, a large supply of labor for transplanting.

Other benefits can be imagined in this environment:

• Reduce the need for transplanting, weeding, and other backbreaking labor. Because of migration to cities, many rural parts of Asia actually suffer from severe labor shortages.
• More efficient use of applied fertilizer

Interspecific hybridization and embryo culture, Thailand, early 1990s

Drs Dayun Tao and Prapa Sripichitt, working at the Department of Agronomy, Kasetsart University, Bangkok, made numerous crosses between rice and wild, rhizomatous species. The difficulty of this work is illustrated by the case of the single successful hybrid they obtained between Oryza sativa and O. longistaminata. To get this one plant, 119 rice florets were pollinated, which produced 51 seeds. Of these seeds, 33 had culturable embryos, and only one of these embryos developed into a viable plant. Put another way, this hybridization was relatively easy: over 3000 pollinations had to be made between rice and O. rhizomatis to get a single viable plant. It was a fortunate cross in other respects: the hybrid was healthy and rhizomatous (it is still alive) and partially fertile allowing F2 seed to be obtained.

Perennial Upland Rice program, Philippines, 1990-2001

To address the problem of erosion in upland rice-growing regions, the International Rice Research Institute (IRRI) initiated a breeding program for perennial upland rice in the mid 1990s. Within just a few years, the program achieved significant progress. The Perennial Upland Rice project team used populations derived from crossing the rice plant Oryza sativa with two different distantly related perennials in the hopes that at least one of these strategies would enable genes from the perennial to be moved to the cultivated rice gene pool.

• • O. rufipogon as donor of perenniality traits. Fertility of the progeny families was generally good, as might have been predicted, given that O. rufipogon is the ancestor of cultivated rice. Many families were perennial, and some of the highest yielding families were the most perennial, suggesting that breeding for both yield and perenniality is feasible.
  • O. longistaminataas donor of perenniality traits. This African species is genetically diverse, strongly perennial and rhizomatous. Rhizomes may be able to survive and spread in drier conditions than stolons. The downside of this donor is that it is more distantly related to cultivated rice and the crosses and backcrosses are much more difficult to make. Descendents of the few successful crosses are mostly infertile, and few were perennial. Interestingly, many of the perennial plants lacked rhizomes. Rhizomes may not be essential for survival, but they may help plants survive stress and they certainly help them spread.

Mapping major rhizome genes, China, 1999-2001

Hu Fengyi, now deputy director of the Food Crops Institute at YAAS, worked on the IRRI perennial-rice project and was senior author of the paper that first reported on mapping of genes for rhizome production in rice. Using the F2 population derived from the Oryza sativa/O. longistaminata cross, two dominant-complimentary genes, rhz2 and rhz3 controlling rhizomatousness were mapped. These were found to correspond with two QTLs associated with rhizomatousness in the genus Sorghum, suggesting that the evolution of the annual habit occurred independently, long after these species diverged. Efforts to map these genes in rice more finely are ongoing. Although other genes undoubtedly contribute to perenniality and rhizomatousness, these two are required in rice. Breeders use markers for these genes to assist in identifying potentially perennial individuals.

Breeding population development, China, 2007-present

The IRRI project was terminated in 2001 because of budget cuts, but the Yunnan Academy of Agricultural Sciences (YAAS) in Kunming has continued the research. Rhizome were considered more stress tolerant than stolons, so they focused on populations derived from crosses with O. longistaminata. As Eric Sacks and colleagues found at IRRI, the plants in these populations mostly lack rhizomes and have a high level of sterility. Finding the extremely rare plants with both rhizomes and fertility has required screening large F2 and Backcross populations.

Goals for Perennial Rice Breeding

Restore seed fertility

Mapping genes that cause partial to complete sterility in many interspecific hybrids. As many as 35 such genes have been mapped in Oryza, and sterility is a big problem in the perennial rice program.

Develop methods for quickly identifying rhizomatous plants

• Marker assisted selection allows large numbers of plants to be screened for rhizome markers. In the field, plants are evaluated first for rhizome production, then for seed fertility, and finally for pollen viability through staining
• Fine mapping of rhizome genes will improve the efficiency of marker-aided-selection or even allow rhizome genes to be cloned and used in recombinant gene techniques.

Eliminate undesirable genes from Oryza longistaminata

Along with potentially useful genes for rhizomes, stress tolerance and disease resistance, undesirable genes from O. longistaminata are also still present in breeding populations. Back-crossing to high-yielding rice varieties is one way to reduce the frequency of these wild alleles.

• Awns: wild Oryza species have awns, but farmers prefer awnless rice.
• Small seed size: wild Oryza species have small seeds, but larger seeds are easier to thresh and clean. Larger seeds germinate more vigorously. Increasing seed size is one way to increase grain yield.
• Altered grain quality: it will be difficult to achieve the flavor and cooking properties of traditional rice varieties. And there are thousands of local varieties with unique properties. Choosing from among the possible quality goals and then achieving them is a "formidable challenge" for all rice breeding programs.
• Low yield: the high yield of elite grain varieties is always compromised by crossing with wild material. However, even low-yielding wild rice species can harbor genes for increasing yield

See also

• Plant breeding
  Plant breeding
  Plant breeding is the art and science of changing the genetics of plants in order to produce desired characteristics. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular...
  
  
• Perennial grain
  Perennial grain
  While many fruit, nut and forage crops are long-lived perennial plants, all major grain crops are annuals or short-lived perennials grown as annuals. Scientists from several nations have argued that perennial versions of today's grain crops could be developed and that these perennial grains could...
  
  
• Hybrid (biology)
• Slash-and-burn agriculture
• Subsistence agriculture
  Subsistence agriculture
  Subsistence agriculture is self-sufficiency farming in which the farmers focus on growing enough food to feed their families. The typical subsistence farm has a range of crops and animals needed by the family to eat and clothe themselves during the year. Planting decisions are made with an eye...
  
  

External links

• Perennial upland rice takes root An article by Paul Cox in the New Agriculturalist.
• The Land Institute A scientific institute in Kansas, U.S.A. with several perennial grain breeding programs.
• the International Rice Research Institute (IRRI)