Parts of the rice plant
Rice plants are similar to other grasses and grains such as oats and wheat. The key difference is that they can grow in standing water or in very wet soil. Rice plants develop clusters of small wind-pollinated ‘flowers’ at the top of the plant called panicles. Once they are pollinated, the flowers develop rice grains.
Although they are perennial (continue to grow from one season to the next), rice plants are treated as annuals: new seeds are usually planted each season for better yields.
To get to the edible rice grain inside the seed the husk has to be removed. Underneath the husk is the rice grain covered with a layer of bran. When rice has its bran intact it is called ‘brown’ rice. Some brown rice grains may even be viable if planted because the ‘germ’ part of the grain, which is the part of the seed that germinates into a new plant, may not have been damaged when the husk was removed. If the bran is also removed, you get ‘white’ rice.
A single rice seed weighs 10–45 milligrams at 0% moisture content. Grain length, width, and thickness vary widely among varieties. Husk weight averages about 20% of total grain weight.
Rice seed can be stored and remain viable from a few weeks if air moisture is below 14%, to as long as a year in drier conditions. Usually rice should be stored in paddy form rather than milled rice as the husk provides some protection against insects. In the International Rice Genebank where rice seed from more than 118,000 different types of rice is conserved, rice seed is kept in vacuum packed, freezers at -18 °C, where they can remain viable for 100 years.
A rice seedling is the young plant that emerges from the rice seed after germination.
A typical young seedling consists of three main parts: the first root (radicle), the first shoot (hypocotyl), and the first leaf (cotyledon).
If the seed develops in the dark – such as when seeds are sown beneath the soil surface – a short stem (mesocotyl) develops, which lifts the crown of the plant to just below the soil surface. After this shoot emerges, it splits and the primary leaf develops.
Once the seedling has about five leaves, it is self-supporting and begins to develop into a more complex plant. This process is called tillering. More stems develop from the main stem – each is a called a new tiller. At the top of each of these new tillers are flatter leaves.
Although the tillers remain attached to the plant, at later stages they produce their own roots and become independent. The amount of tillering depends on the variety of rice and environmental factors such as spacing, light, nutrient supply, and cultural practices.
Once fully developed, at the end of each tiller a flower cluster will develop, which will develop into grains when pollinated.
Once the the rice plant has begun tillering, it needs to develop a more complex root system to anchor the developing plant.
The initial small rootlets that sprang from the seedling develop into mature, fibrous roots, which in turn produce more rootlets. The root system is shallow, with over 95 percent of the roots found in the top 8 inches of soil. All rice roots have root hairs to absorb moisture and nutrients.
The rice root system consists of crown roots(including mat roots) and nodal roots. Both develop from nodes, but crown roots develop from nodes below the soil surface, while nodal roots develop above the soil surface. Nodal roots are often found in rice cultivars growing at water depths above 80 cm. Most rice varieties reach a maximum depth of 1 m or more in soft upland soils. In flooded soils, however, rice roots seldom grow deeper than 40 cm because there is not enough oxygen to supply the growing root tips.
While it might not be obvious because they are not big or colorful, rice plants have flowers. The flowers of rice are more typically referred to by their scientific name – panicles – and they
occur at the end of each tiller. Like most flowering plants, rice needs to be pollinated in order to produce seeds. Rice is mostly self-pollinating, which means that each rice plant can fertilise itself with its own pollen. Cross-pollination between different rice plants does happen, but if plants are separated by a short distance of a few feet or meters it is very rare. Pollination of rice occurs by wind alone – no insects are involved.
Once the rice has been pollinated, the process of grain production begins and the panicles grow heavy with maturing rice grains (seeds).