Rice Fast Facts

Rice field

The History of Rice Production
Asian rice (Orysa sativa L.) seed is the major cereal grain staple for 3 billion people worldwide (FAOSTAT). It represents as much as 70% of calories intake in Southeast and South Asia (FAO STAT) and is integral to several cultures in Asia. Recent molecular evidence suggested that rice was first domesticated in China around 8,000 – 13,500 years ago. The first domestication gave rise to the Japonica-like varieties, from which the Indica types subsequently diverged (Molina et el, 2011). Rice is widely cultivated and consumed in East, Southeast, and South Asia. Through European colonization, it reached Europe and America, but is not as widely consumed in the before mentioned regions.

Rice endosperm and embryo (Photo: IRRI)

Rice Grain Structure
The rice whole grain is the fertilized and fully developed ovary with the hull and awn attached. The de-hulled rice grain, commonly known as brown rice, is called the caryopsis. It is enveloped by the pericarp, tegument, and aleurone layers. Residing inside is the endosperm, which is the nourishing tissue for the embryo, or germ, which will develop into the next generation of rice plant.

Brown (unmilled) vs white (milled) rice (Photo: IRRI)

The milling process will remove the brownish pericarp layers (bran) as well as the embryos from the rice grains. The remaining endosperm, called ‘white rice’, consists mainly of starch and is the part that is used fro rice cooking and consumption.

There are many varieties of rice that differ in bran color, grain morphology and texture after cooking. (CalRice.org)

Rice Use and Nutrition
White rice grains are typically cooked by boiling or steaming and then consumed as whole grain. Rice grains may also undergo the parboil process to enhance their nutritional value in some countries. Rice can also be grounded into a flour, which lacks gluten and is thus good as a gluten-free material. Some rice varieties may have bran with different colors, such as purple or black rice, which may contain antioxidant activity and therefore health benefits.

Japonica vs Indica rice grains (Photo: IRRI)

Rice is often classified into 2 major ecotypes (or subspecies), which are Japonica and Indica varieties. The grain of Indica rice is longer than the Japonica rice. When cooked, Indica rice has a fluffy texture compared to the glutinous ‘sticky’ cooked japonica rice. The kernels of Indica rice stay separated, while those of the japonica varieties tend to stick together once cooked.

Cooked Japonica vs. Indica rice

Rice as a research organism

  • Genome size of 420 Mb with 12 chromosomes
  • Rice genome was completely sequenced (Goff et al, 2002)
  • Diploid
  • Genome contains ~32000 – 50000 genes (Goff et al., 2002).
  • Major mode of reproduction is selfing.
  • Rice has moderate length life cycle and is suitable for both greenhouse and field cultivation.
  • Rice is a model organism for monocot plants with homologs of 98% of the known maize, wheat, and barley proteins (Goff et al, 2002).
  • Genetic transformation is possible.
  • Research efforts are highly co-operative, mainly through International Rice Research Institute (www.irri.org), which is part of the Consultative Group on International Agricultural Research (www.cgiar.org).
  • High quality genome functional annotation query is possible (rice.plantbiology.msu.edu/index.shtml).
  • Mutant collections are available (rmd.ncpgr.cn).
  • TILLING population is also available (tilling.ucdavis.edu/index.php/Rice_results).
  • Information on rice growth, development, morphology, growing practice is very well established (www.knowledgebank.irri.org).

Link to IRRI video (Rice is life in Asia): http://www.youtube.com/watch?v=8VlLEHRJmsM

References

  1. FAOSTAT (http://faostat.fao.org)
  2. Molina, J., Sikora, M., Garud, N., Flowers, J. M., Rubinstein, S., Reynolds, A., ... & Purugganan, M. D. (2011). Molecular evidence for a single evolutionary origin of domesticated rice. Proceedings of the National Academy of Sciences, 108(20), 8351-8356.
  3. Goff, S. A., Ricke, D., Lan, T. H., Presting, G., Wang, R., Dunn, M., ... & Tusneem, N. (2002). A draft sequence of the rice genome (Oryza sativa L. ssp. japonica). Science, 296(5565), 92-100.