Botanical name: Oryza sativa L.
- Rice, an annual grass belongs to the genus Oryza. There are about twenty three species out of which only two species have been known of their commercial value being used for cultivation. These two species are Oryza sativa (Asian rice) and Oryza glaberrima (African rice).
- The Oryza sativa is the most commonly grown species through out the world to day while Oryza glaberrima is grown only in South Africa.
- Of the two, O. sativa is by far the more widely utilized. O. sativa is a complex group composed of two forms endemic to Africa but not cultivated.
- A third form, O. rufipogon, having distinctive partitions spread into South Asian, Chinese, New Guinean, Australian, and American forms.
- In Asia Oryza sativa is differentiated into three sub-species based on geographical conditions, viz., indica, japonica and javanica.
- The variety indica refers to the tropical and sub-tropical varieties grown throughout South and South-East Asia and Southern China.
- The variety japonica is grown in temperate areas of Japan, China and Korea, while javanica varieties are grown along side of Indicas in Indonesia.
Semi-aquatic plant and consists of arenchymatic tissues. The presence of arenchymatic cells on leaf, culm and roots can diffuse oxygen from aerial parts downward to roots.
The plants are about 1m tall but certain deep water varieties can elongate upto 5m with the rise in water level.
The root system is fibrous.
Soon after sowing, rice seed gives out seminal roots out of the radical. These are temporary in nature.
The real functional roots are secondary adventitious roots that are produced from the lower nodes of the culm.
The rice stem known as culm is hollow and is made up of nodes and internodes. Each node bears a leaf and bud, which may grow into a shoot or tiller. Primary tillers grow out of the main culm.
Tillering continues in rice upto vegetative phase.
Some tillers die during the reproductive phase due to competition for water and nutrients. Panicles bearing tillers are known as fertile or productive tillers.
Leaf: Each node of the culm bears a leaf. Each leaf consists of the following parts:
Leaf sheath: It originates from the node of culm and many a times encloses it and sometimes even the next upper node and a part of the leaf sheath of the upper leaf.
Leaf blade: It is the upper expanded part of leaf and begins at node, where it is joined with leaf sheath. At the joint there is a thick collar.
Auricles: These are hairy appendages at the base of the leaf blade.
Ligules: It is a thin papery structure just above the auricles. Different parts of leaf are of importance in identifying the varieties.
Flag leaf: It is the uppermost leaf just below the panicle. It is generally shorter in length and remains erect at an angle
Panicle: The inflorescence of rice plant is born on terminal shoot and is known as panicle. It is determinate type and at maturity it is droopy in nature. Panicle bears the spikelets.
Spikelet: A spkelet is the floral unit and consists of two sterile lemmas, a lemma, a palea and the flower.
Lemma: It is a 5 nerved hardened bract with a filiform extension known as awn. Rice varieties may or may not have an awn.
Palea: It is a three nerved bract slightly narrower than lemma.
Flower: It consists of 6 stamens with two -celled anthers and a pistle with one overy and two stigmas. The pistil consists of one ovule.
Rice grain is the ripened ovary with lemma and palea firmly adhered to it.
The lemma and palea with other smaller components from the hull are removed in shelling rice for consumption.
The rice fruit is a caryopsis in which single seed is fused with the wall of the ovary (paricarp).
The seed consists of endosperm and an embryo. The embryo is very small and is found on the ventral side of the caryopsis. It contains plumule (embryonic leaves) and radicle (root).
On submergence in water or on sowing the radicle grows as root and plumule grows as shoot.