MORPHOLOGY OF THE RICE 1 This is one of the rice production training

modules produced by the International Rice Research Institute.

2 This module is on the morphology of the rice

plant.

3-5 At the end of this lesson, you will be able to:

• identify and describe the morphological

characters of the germinating rice seed and seedling;

• identify the morphological characters of a rice tiller – roots, culm and leaves – and relate them to each other;

• identify and describe the morphological parts of the rice inflorescence or panicle.

1

6 The Asian rice plant, Oryza sativa, is an

annual grass with vegetative parts consisting of roots, culm, and leaves. The roots, culm and leaves form a tiller. At maturity, it may or may not produce an inflorescence called a panicle which bears seeds.

7 When the seed germinates in well-drained

and well-aerated soil, the coleorhiza, a covering enclosing the radicle or primary root, protrudes first.

8 Shortly after the coleorhiza appears, the

radicle or primary root breaks through the covering.

2

9 Two or more sparsely branched seminal roots follow. These roots eventually die and are replaced by many secondary adventitious roots.

10 If the seed germinates in water, the

coleoptile, a covering enclosing the young shoot, emerges ahead of the coleorhiza. The coleoptile emerges as a tapered cylinder.

11 The mesocotyl or basal portion of the

coleoptile elongates when the seed germinates in soil, and in darkness. It pushes the coleoptile above the soil surface.

3

12 The first seedling leaf, or primary leaf, emerges from the growing seed. It is green and shaped like a cylinder. It has no blade.

13 The second leaf is a complete leaf. It is

differentiated into a leaf blade and a leaf sheath.

15 Can you label the parts of these seedlings?

To do this, drag each label into the proper box. If the label stays, that means you got the correct answer. If it doesn’t, try again till you place each of the labels properly. To proceed, click the NEXT button.

4

16 In this section, we are going to study the parts of a tiller. The seedling will grow and develop the branched tillers. The parts of a rice tiller are the roots, the culm and the leaves.

17 Mature roots of the rice plant are fibrous and

produce smaller roots called rootlets. All roots have root hairs to absorb moisture and nutrients. There are 2 kinds of mature roots: secondary adventitious roots and adventitious prop roots.

18 Secondary adventitious roots are

produced from the underground nodes of young tillers.

5

19 As the plant grows, coarse adventitious prop roots often form in whorls from the nodes of the culm above the soil surface.

20 The culm, or jointed stem of rice,

21 is made up of a series of nodes

6

22 and internodes.

23 Young internodes are smooth and solid.

Mature internodes are hollow, finely grooved with a smooth outer surface. Generally, internodes increase in length from the lower to the upper portions of the plant. The lower internodes at the plant base are short and thick.

24 The node is the solid portion of the culm.

The node or nodal region bears a leaf and a bud. The bud is attached to the upper portion of the node and is enclosed by the leaf sheath. The bud may give rise to a tiller.

7

25 Early tillers arise from the main culm in an alternate pattern. Primary tillers originate from the lowermost nodes…..

26 and give rise to secondary tillers.

Secondary tillers produce ….

27 the tertiary tillers.

8

28 The node or nodal region of the culm will bear a leaf.

29 Leaves are borne alternately on the culm in

opposite directions. One leaf is produced at each node. Varieties differ in the number of leaves produced.

30 The topmost leaf below the panicle is the flag

leaf. The flag leaf contributes largely to the filling of grains because it supplies photosynthetic products mainly to the panicle.

9

31 The leaf sheath and leaf blade are continuous.

32 A circular collar joins the leaf blade and the

leaf sheath.

33 The leaf sheath is wrapped around the culm

above the node.

10

34 The swelling at the base of the leaf sheath just above the node is the sheath pulvinus. It is frequently mistermed as the node.

35 Rice leaf blades are generally flat. Varieties

differ in blade length, width, thickness, area, shape, color, angle and pubescence.

36 Note the many parallel veins in the upper

surface.

11

37 The underside of the leaf blade is smooth with a prominent ridge in the middle, the midrib.

38 Most leaves possess small, paired ear-like

appendages on either side of the base of the blade. These appendages are called auricles. Auricles may not be present on older leaves.

39 Another leaf appendage is the ligule, the

papery membrane at the inside juncture between the leaf sheath and the blade. It has either a smooth or hairlike surface. The length, color and shape of the ligule differ according to variety.

12

40 Rice plants have both auricles and ligule. The common grassy weeds found in rice fields normally do not have auricles or a ligule. This characteristic is often helpful in identifying weeds in rice fields when the plants are young.

41 Let us pause to review this section. See if

you can answer these questions. • Distinguish secondary adventitious

roots from the adventitious prop roots. • Identify the leaf blade and the leaf

sheath. • What characters are used to distinguish a

rice plant from a grassy weed? • Differentiate the primary tillers from the

secondary tillers. Again, click on the bullets to view the correct answers. When done, click NEXT to proceed.

42 Name the three parts of a rice tiller by typing

your answers in the appropriate boxes. Click the "CHECK ANSWERS" button to verify your answers. If you want to try again, click "RESET ALL". You may see the correct answers by clicking the “VIEW ANSWERS” button. When done, click the "NEXT" button.

13

43 Can you identify and label these plant parts? Drag each label into the appropriate box. The label will stay if placed correctly. Otherwise, it will go back to its original position. To proceed with the slide show, click NEXT.

44 The terminal component of the rice tiller is an

inflorescence called the panicle. The inflorescence or panicle is borne on the uppermost internode of the culm. The panicle bears rice spikelets which develop into grains.

45 The panicle base often appears as a hair-

like ring, and is used as a dividing point in measuring culm length and panicle length. The panicle base is often called the neck.

14

46 The panicle axis is continuous and hollow except at the nodes where branches are borne.

47 The swellings in the panicle axis where the

branches are borne are the panicle pulvinus.

48 Each node on the main panicle axis gives

rise to primary branches which in turn bear secondary branches. Primary branches may be arranged singly or in pairs.

15

49 The panicle bears spikelets, most of which develop into grains. These spikelets are borne on the primary and secondary branches. A spikelet is a basic unit of the inflorescence or the panicle. It consists of the pedicel and the floret.

50 The floret is borne on the pedicel.

51 The rudimentary glumes are the laterally

enlarged, cuplike apex of the pedicel. The rudimentary glumes are the lowermost parts of the spikelet. During threshing, the rudimentary glumes are separated from the rest of the spikelet.

16

52 The sterile lemmas are small, bractlike projections attached to the floret.

53 The rachilla is a small axis that bears the

single floret. It is between the sterile lemmas and the floret.

54 The rachilla, sterile lemmas, and the

rudimentary glumes all support the floret. The floret includes the lemma, palea and the flower.

17

55 The larger protective glume covering the floret is called the lemma and the smaller one is referred to as the palea.

56 Both the lemma and palea have ridges

referred to as nerves. The lemma has 5, the palea, 3. The middle nerve of the lemma may be smooth or hairy.

57 The lemma has a constricted structure in the

end called the keel. In some varieties, the keel is elongated into a thin extension, the awn.

18

58 In the floret is the flower. The flower consists of a pistil or the female organ,

59 and six stamens or the male organs.

60 The stamens have two-celled anthers borne

on slender filaments.

19

61 The pistil contains one ovule …

62 and bears a double-plumed stigma ….

63 on a short style.

20

64 At the flower’s base near the palea are two transparent structures known as lodicules. The lodicules thrust the lemma and palea apart at flowering to enable the elongating stamens to emerge out of the open floret. The lemma and palea close after the anthers have shed the pollens.

65

The rice grain is the ripened ovary, with the lemma, palea, rachilla, sterile lemmas and the awn firmly attached to it.

66 The rice hull includes the lemma and palea

and their associated structures -- the sterile lemmas, rachilla and awn.

21

67 The dehulled rice grain is called caryopsis, commonly referred to as brown rice because of three brownish pericarp layers that envelope it.

68 Next to the pericarp layers are the two

tegmen layers and the aleurone layers.

69 The remaining part of the grain consists of

the endosperm and the embryo.

22

70 The endosperm provides nourishment to the germinating embryo. The embryo lies on the belly side of the grain and is enclosed by the lemma. It is the embryonic organ of the seed.

71 The embryo contains the plumule, or

embryonic leaves, and the radicle or embryonic primary root.

72 See if you can answer these questions.

• Describe the panicle base and give the

other term for panicle base • What is the basic unit of rice

inflorescence? • What is the term for dehulled rice grain? • What part of the grain provides

nourishment to the germinating embryo? To check on the correct answers, please click on the bullets. When done, proceed to the next slide by clicking the NEXT button.

23

73 Can you label the various parts of the spikelet and the rice flower shown on the slide? Again, drag the labels below to the corresponding boxes. Try to put the labels at the shortest possible time. When done, click the NEXT button to proceed.

74 This concludes our lesson on the Morphology

of the Rice Plant. For further questions, email us at inquiry@irri.exch.cgiar.org.

24

GLOSSARY Aleurone layer - the peripheral layer of the endosperm, containing oil and protein. Adventitious prop roots - roots formed in higher nodes above the soil surface. Auricles - a pair of small, ear-like appendages at the base of the blade, that may not

be present in older leaves. Awn - a thorn-like extension from the keel of the lemma. It is not present in all rice

varieties. Brown rice (caryopsis) - the dehulled rice grain. Bud - a small protuberance on a node. It may give rise to a tiller. Coleoptile - the cylinder-like protective covering of the young plumule. Coleorhiza - the sheath covering the radicle. Collar - the joint between the leaf sheath and leaf blade. Culm - the round, smooth-surfaced, ascending axis of the shoot consisting of hollow

internodes joined by solid nodes. Embryo - the miniature plant developed from the fertilized (diploid) egg called zygote,

which upon germination gives rise to a young seedling. It is located on the ventral side of the seed next to the lemma.

Endosperm - the nutritive tissues of the ripened ovary. It consists of the aleurone

layer and the starchy endosperm. It serves as food for the germinating embryo. Flag leaf - the last leaf just below the panicle. Floret - A unit of the spikelet. It includes the lemma, palea and the flower. Flower - It consists of two lodicules, six stamens and the pistil. Grain - the ripened ovary and its associated structures. Hull - the lemma and palea, and their associated structures. Internode - the smooth, solid (when young), or hollow (when mature) part of the culm

between two successive nodes.

25

Keel - the middle nerve of the lemma. Leaf - the vegetative part of a tiller consisting of the blade and sheath. Leaf blade - the flat and free portion of the leaf. Leaf sheath - the lower part of the leaf, originating from a node and wrapped around

the culm above the node. Lemma - the five-nerved bract of the floret. Ligule - a thin, upright, membranous structure attached to the base of the inside of the

flower. Lodicules - the two scale-like structures near the base of the palea. Mesocotyl - the internode between the coleoptile node and the point of union of the

culm and root in the young seedlings. It pushes the coleoptile above the soil surface.

Midrib - the prominent ridge in the middle of the underside of the leaf blade. Neck (panicle base) - the nearly solid node between the uppermost internode of the

culm and the panicle axis. Node - the solid portion of the culm. It may give rise to a leaf, a tiller, or adventitious

roots. Ovary - the bulbous, basal portion of the pistil which contains one ovule. Palea - the three-nerved bract of the floret. Panicle - the terminal component of the rice plant which bears the rice spikelets. Panicle pulvini - the swellings in the axis of the primary panicle branches. Pedicel - the stalk supporting a spikelet on the panicle branch. Pericarp layer - the wall of the ripened ovary and the outermost layer of cells covering

the seed. Plumule - the embryonic leaves of the young plants in the embryo. It is enclosed by

the coleoptile. Pistil - the female reproductive organ consisting of the ovary, style and stigma.

26

Primary panicle branches - the structures arising from the panicle axis. They bear

the secondary branches. Primary leaf - the first seedling leaf. It does not have a leaf blade. Primary tillers - tillers arising from the lowermost nodes of the main culm. Rachilla - the small axis bearing the single floret. Radicle - the embryonic primary root. Rootlets - the lateral roots that grow endogenously from the mature root. Rudimentary glumes - the laterally enlarged, cup-like apex of the pedicel. Second leaf - the first differentiated leaf with blade and sheath. Secondary adventitious roots - roots arising from the nodes at the base of the plant. Secondary panicle branches - the branches arising from the primary branch of the

panicle. They bear the spikelets. Secondary tillers - tillers arising from primary tillers. Seminal roots - sparsely branched roots that replace the radicle and are later

replaced by secondary adventitious roots. Septum - the cross-sectional layer inside the node which separates adjoining

internodes. Sheath pulvinus - the swelling at the base of the leaf sheath just above the node.

Often mistermed as the node. Spikelet - the basic unit of the rice inflorescence consisting of the two sterile lemmas,

the rachilla and the floret. Stamen - the male reproductive organ consisting of the anther and the filament. Sterile lemmas - the two flowerless bracts at the base of the spikelet. Tegmen layer - two layers of cells next to the pericarp.

27