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Technical Bulletin 4

December, 1965

THE MORPHOLOGY

AND VARIETAL CHARACTERISTICS

OF THE RICE PLANT

TE-TZU CHANGGeneticist

and

ELISEO A. BARDENASAssistant Taxonomist

Illustrated by

ARNULFO C. DEL ROSARIOArtist-Ilustrator

THE INTERNATIONAL RICE RESEARCH INSTITUTE

Los Baos, Laguna, The PhilippinesMail Address: Manila Hotel, Manila


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CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Morphology of the Rice Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Seedling morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Vegetative organs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Culm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Floral organs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Panicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Spikelets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Flower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Trade Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Growth stages of the rice plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Glossary of morphologic terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Botanical and Agronomic Traits Useful in Varietal Classificationand Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Seedling characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Adult plant characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Classification of cultivated varieties of O . sativa . . . . . . . . . . . . . . . . . . . 26

Mutant Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Variations in anthocyanin pigmentation . . . . . . . . . . . . . . . . . . . . . . . . . . 27Variations in non-anthocyanin pigmentation . . . . . . . . . . . . . . . . . . . . . . 27Modifications in size and shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Presence or absence of structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Modifications in structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Modifications in chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Modifications in growth habit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Modifications in other physiological characters . . . . . . . . . . . . . . . . . . . . 28Glossary of mutant traits and gene symbols . . . . . . . . . . . . . . . . . . . . . . . 29

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36


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I n t r o d u c t i o n

The wide geographical distribution of the riceplant ( Oryza sativa L.) and its long history ofcultivation in Asian countries have led to the de-velopment of a great diversity of varietal types.Similarly, workers in various rice-growing coun-

tries use different terms to designate identicalmorphological and physiological characters, agro-nomic traits, gene symbols, and cultural practices.Whereas varietal diversity in germ plasm is desiredin rice breeding, variations in nomenclature hinderscientific communication among the workers.

Workers long have recognized the need for uni-formity in genetic nomenclature of rice. This ledthe International Rice Commission in 1959 to adopta set of genetic symbols. Comprehensive reviewsof genetic studies and linkage analysis have been

published. The International Rice Research Insti-

tute has now assumed the task of monitoring genesymbols.

This publication (1) proposes a set of reason-ably definitive terms that adequately describe thevarious parts of the rice plant and its processedproducts, (2) defines varietal characteristics thatare useful in identification and classification, and(3) describes a number of commonly observed

mutant traits in both morphological and geneticalterms.

In selecting morphological names; terms basedon botanical considerations take priority over ag-

ronomic terms of extensive usage. Synonyms arealso included to provide a basis for concurrent useof terms.

In describing methods for measuring and re-cording varietal characteristics, simple and quickoperations are preferred to elegant techniques thatrequire precision apparatus. Considerable im-portance is given to the economic usefulness ofthe trait under description. Emphasis is also givento growth Characteristics of tropical varietieswhich constitute the bulk of the rice acreage ofthe world. It is recognized that many of the pro-

posed techniques and methods are inadequate todescribe fully. the enormous variation found in cul-tivated varieties or to cover the intricate growth

behavior of the rice plant in different environ-ments. Additional studies are needed to improveexisting methods.

Rice workers are urged to adopt the proposedterms and methods of description, although someof them may appear inadequate, and to suggestways and means of improvement.

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MORPHOLOGY OF THE RICE PLANT

The cultivated rice plant ( Oryza sativa L.) be-longs to the tribe Oryzeae under the sub-familyPooideae in the grass family Gramineae (Poa-ceae) . Biosystematists recently divided the genusOryza into several sections and placed O. sativaunder series Sativa in section Sativae. O. sativa isindigenous to Asia.

O. sativa is a diploid species with 24 chromo-somes. Its genomic formula is AA.

The rice plant may be characterized as an an-nual grass, with round, hollow, jointed culms,rather flat, sessile leaf blades, and a terminal

panicle, Under favorable conditions, the plant maygrow more than one year. As other taxa in thetribe Oryzeae, rice is adapted to an aquatic habitat.

While the ensuing description is based on theubiquitous O. sativa L., the morphologic terms canalso apply to the cultivated species of Africa,O. glaberrima Steud. (2n =24). O. glaberrima dif-

fers from O. sativa mainly in a lack of secondarybranching on the primary branches of the panicleand in minor differences related to pubescence onthe lemmas and length of the ligule. O. glaberrimais strictly an annual.

Seedling Morphology

The grains of rice varieties that lack dormancygerminate immediately upon ripening. In dormantvarieties, a rest period precedes germination andspecial procedures such as heat treatment (50C.for 4-5. days) or mechanical dehulling are neededto break dormancy in freshly harvested samples.

The coleorhiza enveloping the radicle protrudesfirst if germination occurs in an aerated environ-ment such as a well-drained soil. If the grain issubmerged in water, the coleoptile emerges aheadof the coleorhiza.

The primary seminal root (radicle) 1 breaksthrough the coleorhiza shortly after the latter ap-

1Term in parenthesis indicates a synonym.

pears and is followed by two or more secondaryseminal roots, all of which develop lateral roots.Seminal roots are later replaced by the secondarysystem of adventitious roots.

The coleoptile, which encloses the young leaves,emerges as a tapered cylinder. Its color varies

from colorless, pale green to green, 'or pale purpleto purple. The length of the axis between thecoleoptile and the point of union of the root andculm is called the mesocotyl. The elongation of themesocotyl elevates the coleoptile above the ground.The coleoptile later ruptures at the apex and thefirst seedling (primary) leaf emerges. The pri-mary leaf is green and cylindrical and has noblade. The second leaf that follows is differentiat-ed into sheath, blade, ligule, and auricles (Figs. 1and 2).

Vegetative Organs

The rice plant varies in size from dwarf mu-tants only .3 to .4 m. tall to floating varieties morethan 7 m. tall. The great majority of commercialvarieties range from 1 to 2 m. in height. The vege-tative organs consist of roots, culms, and leaves.A branch of the plant bearing the culm, leaves,roots and often a panicle is a tiller.

1. Roots

The roots are fibrous, possessing rootlets androot hairs. The seminal roots are sparsely branched

and persist only for a short time after germina-tion. The secondary adventitious roots are prod-uced from the underground nodes of the youngculms and are freely branched. As the plant grows,coarse adventitious prop roots often form inwhorls from the nodes above ground level. Someof the adventitious roots are positively geotropic,while others may be diageotropic. In floating va-rieties, fine branched roots form from the highernodes on the- long culm below the water surface.

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and the base of the sheath pulvinus. The bud maygive rise to a tiller. Adventitious roots appear inthe axis at the base of the internode. The septuminside the node separates two adjoining internodes.The mature internode is hollow, finely grooved,and glabrous on the outer surface. The nodal sep-tum and internode may be differentially pig-mented.

The internodes of a culm vary in length, gen-

erally increasing from the lower internodes to the

Adventitious roots arise in both nodes and inter-nodes and are usually found in the earlier formedones.

2. Culm

The jointed stem of rice, called a culm, is madeup of a series of nodes and internodes. The node(nodal region) bears a leaf and a bud. The budis inserted in the axil between the nodal septum

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upper ones. The lower internodes at the base ofthe culm are short and thickened into a solid sec-tion. A visually detectable internode (more than5 mm. long) is considered as elongated. The inter-nodes also vary in cross-sectional dimension, thelower ones being larger in diameter and thicknessthan the upper ones.

Tillers arise from the main culm in an alter-

nate pattern. The primary tillers originate fromthe lowermost nodes and give rise to secondarytillers (Fig. 3). The latter give rise to tertiarytillers.

3. Leaves

The leaves are borne on the culm in two ranks,one at each node (Fig. 3). The leaf consists of thesheath and blade. The leaf sheath is continuouswith the blade. It envelops the culm above thenode in varying length, form, and tightness. Aswelling at the base of the leaf sheath just abovethe point of its insertion on the culm is the sheath

pulvinus. The sheath pulvinus is usually above thenodal septum and is frequently mistermed thenode.

The blades are generally flat and sessile. Varie-ties differ in blade length, width, area, shape,color, angle, and pubescence. The uppermost leafbelow the panicle is the flag leaf. The flag leafgenerally differs from the others in shape, size,and angle. Varieties also differ in leaf number.

The upper surface of the blade has manyridges formed by the parallel veins. The most pro-minent ridge on the lower surface is the midrib.

Auricles are small, paired, ear-like appendagesborne on either side of the base of the blade. Atthe junction of the blade and sheath on the insideis a membranous, glabrous or ciliate ligule. Theligule varies in length, color, and shape from varie-ty to variety. The junction of the sheath and bladeis the collar or junctura. The collar often appearsas a raised region on the back of the leaf. Thesheath pulvinus, auricles, ligule and collar on thesame plant may be differentially pigmented. Whenpigmented, the dorsal, ventral and lateral parts ofthe collar may slightly differ in color. The auriclesmay not persist on older leaves.

The main culm bears the largest number ofleaves. The leaf number on a tiller decreases prog-ressively with the rise in tillering order. The firstrudimentary leaf at the base of the main culm isa bladeless, 2-keeled bract, the prophyllum. Themargins of the prophyllum clasp the young tillerwith its back against the parent culm (Fig. 3).The prophyllum is also present between each sec-ondary tiller and its tertiary tiller.

Floral Organs

The floral organs are modified shoots. Thterminal shoot of a rice plant is a determinate inflorescence, the panicle (Fig. 4). A spikelet is thunit of the inflorescence. The spikelets are pediceled on the branched panicle. The spikelet consistof the two sterile lemmas, the rachilla and the floret. A floret includes the lemma, palea and the en

closed flower. The flower consists of six stamenand a pistil, with the perianth represented by thlodicules.

1. Panicle

The panicle is borne on the uppermost internode of the culm which is often mistermed a peduncle. The extent to which the panicle and portion of the uppermost internode extend beyonthe flag leaf sheath determines the exsertion othe panicle. Varieties differ -in degree of exsertion

The nearly solid node between the uppermointernode of the culm and the axis of the paniclis the panicle base. This node generally does no

bear a leaf or a dormant bud but may give risto the first 1-4 panicle branches. The panicle basoften appears as a ciliate ring and is used as dividing point in measuring culm length anpanicle length, The region about the panicle basis often called the neck.

The panicle axis (rachis) is the main axis othe inflorescence, extending from the panicle basto the apex, It is continuous and hollow except athe nodes where the panicle branches are borneThe swellings in the axils of the panicle wherthe branches are borne are the panicle pulvini.

The panicle has a racemose mode of branchinin which each node on the main axis gives risto the primary branches and each of which in turbears the secondary branches. The secondarbranches bear the pediceled spikelets. The primarbranches may be arranged in a single or pairefashion.

Varieties differ greatly in the length, shapeand angle of the primary branches, and in thweight and density (number of spikelets per unof length) of the panicle.

2. Spikelets

The spikelet is borne on the pedicel which imorphologically a peduncle. The apex of the pedicel below the sterile lemmas is expanded into lobed facet of varying size, shape, and marginStapf and other systematists (cf. Chevalier 1937considered the spikelet of Oryza as comprisinthree fiowers, two of which were reduced in development. Thus, the enlarged, cup-like apex i

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Fig. 3. Parts of a primary tiller and its secondary tiller.

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Fig. 4. Component parte of a panicle (partly shown in this illustration).

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Fig. 5. Parts of a spikelet.

homologous with a pair of true glumes and maybe termed the rudimentary glumes.

A spikelet consists of a minute axis (rachilla)on which a single floret is borne in the axils of2-ranked bracts (Fig. 5). The bracts of the lower

pair on the rachilla, being always sterile, are thesterile lemmas (glumes, empty glumes, outerglumes)2. The upper bracts or the floweringglumes consists of the lemma (fertile lemma) andpalea. The lemma, palea, and the included flower

form the floret.The sterile lemmas are generally shorter than

the lemma and palea, seldom exceeding one-third

2As Stapfs interpretation is followed, the pair of bractsabove the rudimentary glumes should be designated as thesterile lemmas. Therefore, such terms as glumes, emptyglumes, outer glumes, and non-flowering glumes should beplaced within inverted commas, e.g., empty glumes.

the length of the latter. The sterile lemmas maybe equal or unequal in size, the upper one gen-erally being larger.

The lemma is the larger, indurate (hardened),5-nerved bract which partly envelops the smaller,3-nerved palea. The middle nerve or keel may beciliate or smooth. The extended tips of the lemmaand the palea are the apiculi. The apiculi may beseparated into lemmal apiculus and paleal apiculus.The awn is a filiform extension of the keel of the

lemma. The surface of the lemma and the paleamay be pubescent or glabrous. In some varieties,a pair of lateral nerves on each side of the centralnerve of the lemma may fuse to form a knob-likemucro on either side of the lemmal apiculus.

During natural shattering or the threshing pro-cess, the spikelet is separated from the pedicel atthe junction of the lower sterile lemma and the

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facet (rudimentary glumes) . The base of the lowersterile lemma as is disarticulates from the pedicelis horizontal or oblique in appearance. The rela-tive degree of development of the abscission layerbetween the sterile lemmas and tile facet is report-ed to be associated with the ease of shedding. Somevarieties are threshed by the fracture of the pedi-cel rather than by disarticulation.

3. Flower

The flower proper consists of the stamens andpistil. The six stamens are composed of 2-celledanthers borne on slender filaments. The pistil con-tains one ovule. The short style bears the bifur-cate, plumose stigma.

The lodicules are two wale-like, transparent,fleshy structures located at the base of the floweradnate to the palea. They represent the reduced

perianth (calyx and corolla), At anthesis, the lodi-cules become turgid and thrust the lemma andpalea apart, allowing the elongating stamens to

emerge above or outside the open floret. Antherdehiscence may coincide with the opening of thelemmas, or immediately precede or follow it. Thelemma and palea close after the pollen grains areshed from the anther sacs.

The rice fruit is a caryopsis in which the singleseed is fused with the wall of the ripened ovary(pericarp), forming a seed-like grain. The grainis the ripened ovary, with the lemma, palea, rachil-la, sterile lemmas, and the awn, if present, firmlyadhered to it (Fig. 6). The lemma and palea andtheir associated structures such as the sterile lem-mas, rachilla, and the awn whenever present con-

stitute the hull or husk.

The dehulled rice grain (caryopsis) is calledbrown rice because of the brownish pericarp. Redrice owes its trade name to the red pericarp and/or the red tegmen. The tip of the caryopsis is some-what oblique, corresponding to the larger size ofthe lemma than that of the palea. The surface ofthe caryopsis has ridges which correspond to thoseof the lemma and palea.

The caryopsis is enveloped by the pericarp. Thepericarp is fibrous and varies in thickness. Nextto the pericarp are two layers of cells representingthe remains of the inner integuments, the tegmenor seed coat (often mistermed the testa).

The embryo lies on the ventral side of thespikelet next to the lemma. The remaining part ofthe caryopsis is the endosperm which providesnourishment to the germinating embryo. The hilumis a dot adjacent to the embryo marking the pointof attachment of the caryopsis to the palea. An-other scar at the tip of the caryopsis marks the

base of the style.

Fig. 6. Structure of a grain (adapted from Grist, 1959).

The embryo contains the embryonic leave(plumule) and the embryonic primary root (radicle). The plumule is enclosed by the coleoptile andthe radicle ensheathed by the coleorhiza; thesform the embryonic axis, The embryonic axis i

bounded on the inner side by the scutellum (cotyledon) which lies next to the endosperm. The coleoptile is surrounded by the scutellum and th

epiblast, the vascular trace which is fused with thlateral parts of the scutellum.

The endosperm is enclosed by the aleuronlayer which lies beneath the tegmen. The whitestarchy endosperm consists of starch granules embedded in a proteinaceous matrix. In the waxy(glutinous) varieties, the starch fraction is com

posed almost entirely of amylopectin and stainreddish-brown with weak potassium iodide-iodinsolution. In the common, non-waxy (non-glutinous) types, the starch fraction contains amylosin addition to amylopectin and stains dark bluewith potassium iodide-iodine solution. The starchyendosperm also contains sugars, fats, crude fiberand inorganic matter.

Chalky white spots often appear in the starchyendosperm. Soft textured, white spots occurring inthe middle part on the ventral side (side on whichthe embryo lies) are called white bellies. A whitechalky region extending to the edge of the ventraside and. toward the center of the endosperm icalled a white core. A long white streak on thedorsal side is called the white back

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Trade TermsDuring the process of milling and polishing,

the hull is first removed from the grain (tradename: rough rice or paddy) in a sheller. The peri-carp, tegmen, embryo; aleurone layer, and a smallportion of the starchy endosperm are then re-moved as the bran. In the U.S. rice trade, the

coarse outer bran layers, the embryo (germ) andsmall bits of endosperm constitute the rice bran.The rice polish (white bran) refers to the innerlayers of the bran removed during polishing. The

bulk of the starch endosperm remains as the totalmilled rice (polished rice).

In U.S. trade terms, total milled rice is separat-ed into head rice (whole kernels), second heads(broken kernels at least half as long as a wholeone), screenings (broken pieces about 1/4 to 1/2the length of a whole kernel), and brewers' rice(broken pieces which can pass through a 5/64-

inch sieve). The corresponding trade termsproposed by the Food and Agriculture Organiza-tion of the United Nations (FAO) are: whole riceor head rice (whole or nearly whole kernels), bigbrokens or second heads (broken kernels equal toor greater than half the length of a whole kernel),medium brokens (broken pieces between 1/2 and1/4 the length of a whole kernel), small brokens(broken pieces which are smaller than 1/4 of akernel but do not pass a sieve with perforationsof 1.4 mm. or 0.055 inch), chips (small chips or

particles of a kernel which can pass through asieve having perforations of less than 1.47 mm.)and split kernels (pieces caused by a longitudinal

splitting of the kernel).

Rough rice in the United States yields about20 percent hulls, 8 percent bran, 2 percent pol-ish, and 70 percent milled rice. Actually, the rela-tive proportions of the above components varygreatly among rice varieties of any particulargeographic region.

Parboiled rice is rough rice which has been sub-jected to a steam or hot water treatment prior tomilling. Parboiling increases the percentage ofhead rice and the vitamin content of milled rice.

Enriched rice is a blend containing ordinary milledrice and a small percentage of milled rice heavilyfortified with thiamin, niacin, and iron phosphateto raise the vitamin and iron content slightly abovethe level present in brown rice. When the yellow-colored riboflavin is added to the enriching agents,white pigments such as calcium oxide, talc, andtitanium dioxide are also included in the enrichingmixture to make the finished product appear white.

Growth Stages of the Rice Plant3

The vegetative phase of the rice plant beginswith grain germination which is signified by theemergence of the radicle or coleoptile from the ger-minating embryo. This is followed by the pre-till-ering stage during which seminal and lateral rootsand the first few leaves develop while the contents

of the endosperm are absorbed by the growingseedling. The tillering stage starts with the ap-pearance of the first tiller from the axillary budin one of the lowermost nodes. The increase intiller number continues as a sigmoid curve until themaximum tiller number is reached, after whichsome tillers die and the tiller number declines andthen levels off. The visible elongation of lowerinternodes may begin considerably earlier than thereproductive phase or at about the same time.

The reproductive phase may begin before themaximum tiller number is reached, or about the

period of the highest tillering activity, or there-

after. This phase is marked by the initiation ofthe panicle primordium of microscopic dimensionsin the main culm. Panicle development continuesand the young panicle primordium becomes visibleto the naked eye in a few days as a hyaline struc-ture 1-2 mm. long with a fuzzed tip. The develop-ing spikelets then become distinguishable. The in-crease in the size of the young panicle and its up-ward extension inside the upper leaf sheaths aredetectable as a bulge in the rapidly elongatingculm, often called the booting stage. When the au-ricles of the flag leaf are directly opposite the au-ricles of the next lower leaf, meiosis is usually.occurring in the microsporocytes (pollen mothercells) and macrosporocytes of the panicle. This isfollowed by panicle emergence from the flag leafsheath, commonly called heading. Anthesis or

blooming begins with the protrusion of the firstdehiscing anthers in the terminal spikelets on the

panicle branches. Pollination and fertilization fol-low. The development of the fertilized egg andendosperm becomes visible a few days followingfertilization. Grain development is a continuousprocess, but agronomic terms such as the milkstage, soft dough stage, hard dough stage, andfully ripe stage are often used to describe the dif-ferent stages.

As the grains ripen, the leaves become senescent

and turn yellowish in an ascending order. The non-

3The terms used were largely adapted from a tentative,unpublished nomenclature of growth stages of the rice plantproposed by a committee appointed during the Symposiumon the Mineral Nutrition of the Rice Plant held at TheInternational Rice Research Institute, February 23-28,1964. The members of the committee are R. Best, T. F.Chiu, N. S. Evatt, S. Matsushima, C. P. Owen, A. Tanaka,and N. Yamada.

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functioning leaves and culm tissues are termeddead straw. in some varieties, the culms and up-

fully ripe.

Under favorable growth conditions, new tillersmay grow from the stubble of the harvested plants.The second and subsequent harvests from the crop

spectively.

per leaves may remain green when the grains are

are called the first and second ratoon crops, re-

Glossary of Morphologic Terms

1. ABSCISSION LAYER (syn. point of dis-articulation, point of spikelet separation).Layer of cells related to the separation of a

plant part, such as a leaf or fruit, from theplant. Structural changes (dissolution) in theabscission layer precede separation. In rice,the thickness of the abscission layer betweenthe spikelet and the pedicel is reported to beassociated with the ease of shedding in certain

varieties.2. ALEURONE LAYER. The peripheral layer

of the endosperm, containing oil and proteinbut no starch.

3. APICULUS. The extending tip of .the lemmaor palea. The two apiculi may be distinguishedas lemmal apiculus and paleal apiculus.

4. AURICLES (syn. sickles). A pair of small,ear-like appendages borne at the base of the

blade and usually arising at the sides wherethe ligule and the base of the collar are joined.This structure may not persist on the olderleaves.

5. AWN (syn. arista, beard). A filiform exten-sion of varying lengths from the keel (middlenerve) of the lemma.

6. BLADE (syn. lamina). The linear-lanceolate,flat, sessile and free portion of the leaf. It iscontinuous with the leaf sheath. Blades on thesame plant differ in length, width, and angleof insertion.

7. BROWN RICE (syn. husked rice, cargo rice).The caryopsis or dehulled grain.

8. CARYOPSIS (syn. brown rice). The maturefruit of grasses in which the seed coat firmly

adheres to the pericarp.

9. COLEOPTILE (syn. sheathing leaf, "firstleaf"). The cylinder-like, protective coveringthat encloses the young plumule. It persistsonly for a short time after germination.

10. COLEORHIZA. The sheath covering theradicle.

11 . COLLAR (syn. junctura, neck, leaf cushion)The joint between the leaf sheath and balde.

leaf sheath and blade.The collar usually differs in color from the

12. CULM (syn. stem, haulm). The round

consisting of hollow internodes jointed by

ventitious roots and axillary buds, it may be

primary, secondary, or tertiary, depending on

13. EMBRYO (syn. germ, eye). The miniaturplant developed from the fertilized (diploid)egg, the zygote, which upon germination giverise to a young seedling. The basic parts of amature embryo are the embryonic axis and thescutellum. The embryo is appressed to the endosperm by the scutellum. The embryo lies onthe ventral side of the caryopsis next to thelemma., It is easily detached and removed inthe milling process as pert of the bran.

14. EMBRYONIC AXIS. The plumule enclosed bthe coleoptile and the radicle ensheathed bythe coleorhiza form the embryonic axis in theembryo.

15. ENDOSPERM. Nutritive tissues of the ripened ovary, consisting of the aleurone layeand the starchy endosperm. The endosperm itriploid, derived from the fertilization of twopolar nuclei in the embryo sac by one spermnucleus from the pollen tube.

16. EPIBLAST. A small structure opposite thscutellum in the embryo. Sometimes. . . consid

vascular tissue.

lemma, palea, and the enclosed flower.

18. FLOWER. The two lodicules, six stamens, anthe pistil.

19. GRAIN (syn. rough rice, paddy, caryopsisseed). The ripened ovary and its associatestructures such as the lemma. palea, rachillasterile lemmas, and the awn if present. Sterilor under-developed ovaries enveloped by well-developed lemma and palea should btermed empty or under-developed spikelets.

the point of attachment to the palea.

ma ana palea. Structures such as the rachillasterile lemmas, the awn if present, and brokesegment of the pedice1 are usually associatewith the hull, if they survive the threshinprocess.

smooth-surfaced ascending axis of the shoot

solid nodes. It bears the leaves, panicle, ad-

tillering order.

ered to be a rudimentary cotyledon. It has n

17. FLORET. A unit of the spikelet, including th

20. HILUM. A scar on the caryopsis indicatin

21. HULL (syn. husk. chaff). Includes the lem

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22.

23.

24.

25.

26.

27.

28.

29,

30.

31.

32.

33.

INTERNODE. The smooth, solid (whenyoung) or hollow (when mature) part of theculm, short basally and long apically, betweentwo successives nodes.

LEAF SHEATH (syn. sheath, vagina). Thelower part of the leaf, originating from a nodeand enclosing the internode above it and some-times the leaf sheaths and blades of the suc-

ceeding internodes.

LEMMA (syn. ferti1e lemma, floweringglume, glume, outer glume, lower palea,

palea inferior, valve). The indurate (hard-ened), 5-nerved bract of the floret partly en-closing the palea,

LIGULE. A thin, upright, membranous struc-ture seated on the inside of the collar at itabase where the blade joins the leaf sheath. Itis often bilobed, ciliate or glabrous.

LODICULES. The two scalelike structureswhich are adnate to the base of the palea.

They represent the rudiments of the perianth(calyx and corolla).

MESOCOTYL. The internode between thescutellar node and the coleoptile in the embryo.In the young seedling, mesocotyl is the inter-node between the coleoptile node and the pointof union of the culm and root. Its length canbe measured only when the seedlings aregrown in the dark or from the underground

portion of the seedling,

MUCRO (syn. glandular process). A smallbulge on either side of the lemmal apiculusformed by the fusion of the two lateral nerves.

NODAL SEPTUM. The solid partition in thenode separating two adjoining internodes.

NODE. The solid portion of the culm, panicleaxis, and panicle branches. From the axils ofnodes on the culm may arise a leaf, a tiller, oradventitious roots; from nodes on the panicle,the branches or spikelets.

NON-WAXY ENDOSPERM (syn. common,non-glutinous rice). Starchy endosperm inwhich the starch fraction contains both amy-lose and amylopectin. It stains dark blue withweak potassium iodide-iodine solution. The

non-waxy type cooks drier than the glueywaxy type.

OVARY. The bulbous, basal portion of thepistil containing one ovule.

PALEA (syn. palet, pale, upper palea, paleasuperior, inner glume, glume, floweringglume, valvule). The indurate, 3-nerved bractof the floret which fits closely to the lemma.It is similar to the lemma but narrower,

keeled, with a median bundle but with nostrong midnerve on the back. The two othernerves are close to the margins.

34. PANICLE (syn. inflorescence, head, ear).The determinate inflorescence of rice with aracemose mode of branching, bearing pedi-celed spikelets and flowering from the apexdownward.

35. PANICLE AXIS (syn. rachis, rhachis). Thedistinctly grooved, main axis of the panicle,extending from the base to the apex. The axisis hollow except at the regions (nodes) wherethe primary panicle branches are borne.

36. PANICLE BASE. The nearly solid node be-tween the uppermost internode of the culmand the main axis of the panicle. This nodegives rise to the first primary branches ofthe panicle (1-4) and usually bears no leafor dormant bud.

37. PANICLE PULVINUS. A swelling in the

axils of the primary panicle branches, morenoticeable during panicle emergence.

38. PEDICEL (syn. foot stalk, peduncle). Thestalk supporting a spikelet on the paniclebranch. The distal end appears as a lobed cup,representing two rudimentary glumes (facet).

39. PERICARP. The wall of the ripened ovary,consisting of layers of cells which form a pro-tective covering around the seed. The pericarplayers may be differentiated into epicarp, me-socarp and endocarp. The pericarp is derivedfrom diploid maternal tissue. It is light brown,speckled reddish-brown, red or purple.

40. PLUMULE. The embryonic leaves of theyoung plant in the embryo. It is enclosed bythe coleoptile.

41. POLLEN GRAINS. The minute, spheroidalstructures (spores) in the anthers of a floret.They are microgametophytes, consisting of ahaploid tube nucleus and a haploid generativenucleus. Upon germination, the pollen tubecontaining a tube nucleus and two sperm nu-clei (gametes) grows down through the style,

penetrates into the embryo sac, and the spermnuclei achieve the double fertilization process.

42. PRIMARY LEAF (syn. prophyll, secondleaf). The first seediing leaf without a bladethat emerges next to the coleoptile.

43. PROPHYLLUM (syn. coleoptyloid) . A small,2-keeled bract enclosed by the leaf sheath withthe back against the parent culm and itsmargins clasping the young tiller.

44. RACHILLA (syn. rhachilla, callus). A dimi-nutive axis between the rudimentary glumes,

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the sterile lemmas, and the fertile floret. Itrarely branches.

45. RADICLE. The embryonic primary root en-sheathed by the coleorhiza and the root cap?persisting only for a short time after germina-tion.

46. ROOTS. The organs of absorption and anchor-

age, growing opposite the shoot, comprisingthe short-lived seminal roots and adventitioussecondary roots which arise from the lowernodes of the culm.

47. RUDIMENTARY GLUMES (syn. glumes,vestigial glumes, first and second glumes,facet). The true glumes of .a typical grassspikelet which are reduced to minute lobes inrice, opposite one another at the tip of thepedicel.

48. SCUTELLUM (syn. cotyledon). The portionof the embryo partly surrounding the embryo-nic axis, containing oil and protein for the

germinating plant. It serves as an absorbingorgan to transfer nutrients from the endos-perm to the young seedling.

49. SEED. The mature, fertilized egg includingthe seed coat, embryo and endosperm. In rice,the seed coat is firmly adhered to the mater-nal pericarp. Therefore, the seed is an in-separable part of the fruit (caryopsis). Theterm seed, as used in seeding or sowing, ac-tually refers to the grain.

50. SHEATH PULVINUS (syn. sheath joint). Asmall swelling at the base of the leaf sheath

just above its point of insertion on the culm.Often mistermed the node.

51. SPIKELET. A unit of the rice inflorescenceconsisting of the two sterile lemmas, the ra-chills and the floret. The two rudimentaryglumes are considered to be a part of thespikelet.

52. STARCHY ENDOSPERM. The bulk of theendosperm within the aleurone layer, consist-ting largely of starch granules embedded ina proteinaceous matrix. The starchy endos-

perm also contains sugars, fats, and fibers.The bulk of the starchy endosperm survivesthe milling and polishing process as the milledwhite rice.

53. STERILE LEMMAS (syn. glumes, emptyglumes, outer glumes, lower and upperglumes, "non-flowering glumes, first andsecond glumes, sterile glumes, lower and up-per empty lemmas). The two flowerless bractsat the base of the spikelet. The two sterilelemmas may differ in length and shape.

54. TEGMEN (syn. seed coat). The two layers ofcells lying next to the pericarp, representingthe inner cell layers of the inner integumentsof the ovule. The tegmen is often mistermed astesta which is derived from the outer inte-guments of the ovule and which is destroyedbefore the caryopsis ripens.

55. TILLER (syn. stool, branch, innovation). Theintravaginal vegetative branch of the riceplant, typically including roots, culm andleaves, but which may or may not develop apanicle. The primary tillers originate fromthe lower nodes of the main culm. The primarytillers give rise to secondary tillers and thelatter to tertiary tillers. All tillers arise in analternate pattern.

56. WAXY ENDOSPERM (syn. glutinous rice).Starchy endosperm in which the starch frac-tion is composed almost entirely of amylopec-tin. It stains reddish brown with weak potas-.sium iodide-iodine solution. Waxy endospermhas an opaque appearance. It is glutinousin character, i.e., it becomes pasty and stickywhen cooked. However, the waxy type of en-dosperm does not contain gluten. Rice pastriesand high-quality rice wine are made frommilled waxy rice.

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BOTANICAL AND AGRONOMIC TRAITS USEFULIN VARIETAL CLASSIFICATION AND IDENTIFICATION

The thousands of cultivated varieties (cultivars)of O. sativa L. vary greatly in growth habit,form, size and structure. A strict botanical classi-

fication based on morphological differences doesnot provide sufficient criteria to embrace theenormous diversity in rice. Economic traits of a

physiological, pathological, or quantitative naturemay be used to aid in varietal identification. Insuch cases, it is desirable to indicate the environ-mental conditions under which the particular traitor traits were observed, e.g., latitude, growing

period, cultural methods, essential meteorologicaldata, and soil fertility level.

The commonly used plant characteristics andthe methods of recording them are enumerated be-low. Some of these are being used to catalog TheInternational Rice Research Institutes collection

of 10,000 cultivated varieties. As some of the cri-teria are empirical measures, they may be modifiedto suit local needs. Standards may be based onlocal varieties if such standards are indicated inthe published results. Information on samplingmethods or sample sizes for quantitative traits maybe obtained from Institute publications (IRRI1964, 1965; Oate 1964; Oate and Moomaw1965).

For quantitative traits which continuously varywithin a variety when grown under different en-vironments, such as height, maturity and size, phy-sical measurements are more meaningful thangeneralized descriptive classification of tall andshort, early and late, and others. Experimentsshowed that certain characters which were believedto exhibit discontinuous variation such as awnlength, grain shedding, grain weight, grain dor-mancy, and intensity of pigmentation have shownmarked variability when the plants are grown un-der different sets of environments.

Some of the exotic or extreme types are de-scribed under Mutant Traits which follows.

Seedling Characteristics

1. Seedling height: For seedlings grown in the

seedbed or directly sown in the field, the distance(in cm.) is measured from the base of the plantto the tip of the longest leaf of seedlings pulledat random at a given date (14-21 days) followingseeding. Although varieties differ greatly in seed-ling vigor and rate of growth, there is no precisedefinition or means of measuring seedling vigor.Prompt emergence and rapid growth are generallydesired in commercial varieties, particularly thosedesigned for direct seeding.

2. Juvenile growth habit: Juvenile growthhabit may be measured from the angle of the tillersobserved from the entire plot prior to the maximumtillering stage.

a. Erect - an angle of 30 or less from theperpendicular.

b. Spreading - tillers have a pronouncedspreading habit, leaning more than 60from the perpendicular.

c. Intermediate - the angle is intermediatebetween erect and spreading.

Plants with prostrate habit in early growth mayassume a less spreading form later in their lives.Juvenile plants of the intermediate type are less

prostrate than those with the spreading habit.

3. Leaf color:

a. Blades: Foliage color is readily distin-guished in the seedling stage. Standardcolor charts for plant tissues are availablefrom the Munsell Color Charts for PlantTissues (1963).

b. Leaf sheath : The sheath color of the lowerleaves is readily classified. Color classes areshades of green, red, and purple. Descrip-tion and color plates are given by Hutchin-son et al. (1938) and Ghose et al. (1960).

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4. Resistance to blast and other diseases: Seed-ling leaf reaction to the blast fungus (Piriculariaoryzae) can be readily determined in a blast diseasenursery. Operational details may be obtained fromthe procedure for establishing a Uniform Blast

Nursery (Ou 1965) ., Varieties also differ marked-ly in seedling reaction to the bacterial streak di-sease, Xanthomonas translucens f. sp. oryzae ( X.oryzicola ) , the bacterial leaf blight disease (X. ory-

zae ), and virus diseases (IRRI 1965, 1966).

5. Length of mesocotyl, coleoptile and primaryleaf : Mesocotyl length is measured from 7-day oldseedlings germinated at about 30C. in total dark-ness. Mesocotyl and coleoptile development mayserve as indices of seedling vigor during emergence.Length ratios of primary leaf/coleoptile and meso-cotyl/coleoptile may also be used to differentiatevarieties (cf. Nagai 1958).

6. Root color: Colorless (white) or red (undersunlight). As roots grow older, colorless roots mayturn reddish brown because of the deposit of ferrichydroxide on the root surface.

7. Seedling reactions to specific chemicals:Varieties differ in their seedling reactions to spe-cific chemicals. For instance, most of the tropicalindica varieties are susceptible to the phytotoxicityof organo-mercuric fungicides, whereas the japo-nica varieties are largely resistant. The differen-tial effect of herbicides on rice varieties may alsobe used to differentiate varieties.

Additional tests for physiological characters ofrice seedlings have been described by Oka (1958).

Adult Plant Characteristics

The characteristics of the adult plant are re-corded during or shortly after anthesis. Some floralorgans may also lose their color or fade as theplant matures. Therefore, when recording pig-mentation it is desirabIe to indicate whether the

plant is at the blooming or mature stage.

1. Blade: The uppermost leaf below the flagleaf on the main culm is taken as a representative

blade.

a. Pubescence : Pubescent or glabrous (includ-ing smooth surface and ciliate margins).

b. Length: The distance (in cm.) from the

junction of the blade and leaf sheath to thetip of the blade.c. Width: Measured at the widest portion of

the blade.d. Area: Leaf area can be estimated by the

product of length and width.e. Color: Green is divided into pale green,

green, and dark green. Standard color chartsmay be referred to for finer differentiations.Other colors are full purple, purple stripes,

purple margins, and purple wash of aspreading type (Ramiah and Rao 1953).

f . Angle : Two measurements can be taken onthe same blade. One is the angle of attach-ment of the blade measured near the collar.The other is the angle of blade opennessmeasured up to the apex of the blade. Indescriptive terms, blade angle may be classi-fied as erect (angle of attachment and angle

of blade openness nearly equal, straightblade), recurvate at the tip (angle of bladeopenness slightly larger than the angle ofattachment., blade largely straight and erectbut curved near its tip), curving (angle ofopenness larger than that of attachment,

blade gently curving throughout its length)and drooping (angle of openness muchlarger than that of attachment, blade gener-ally long and its- tip dips lower than thecollar).

2. Angle of flag leaf: Angle of 0-30' at fullblooming is rated erect; 31-60, intermediate: 61-

90, horizontal ; and 91 or more, descending.3. Leaf sheath: Sheath color is taken on the

first leaf below the flag leaf. Colors of the sheathon the outside are green, several shades of purple,full purple, purple stripes, and purple lines. Sheathcolor variations have been illustrated by Hutchin-son et al. (1938), Ramiah and Rao (1953). andGhose et a1. (1960).

The color of the inside sheath base (sometimescalled the leaf axil) just above the pulvinus is an-other taxonomic criterion. It varies from colorless(white) to green and shades of purple.

recorded on the first leaf below the flag.

4. Ligule: Characteristics of the ligule are also

a. Pubescence of fringes: glabrous or ciliate.b. Length: short (5-19 mm.), medium (20-34

c. Color: colorless (white), and shades of

5. Auricles: Auricles are examined for presenceor absence, coloration (colorless, or shades of

purple), length and density of pubescence.

6. Collar: The collar may be colorless (white),green or purple.

7. Culm: Characteristics such as outer diame-

ter, length, and color are recorded on the mainculm at full blooming.

a. Outer diameter (in mm.) : the lowestelongated internode which is longer than 5cm.

b. Color of internode surface: green, gold,shades of purple and purple lines. Color

plates have been given by Hutchinson et al.(1938), Ramiah and Rao (1953), and Ghose

mm.), and long (35-50 mm.).

purple.

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et al. (1960).c. Length: The distance in centimeters from

the ground level to the panicle base.d . Number: Culm or tiller count includes both

panicle-bearing and non-bearing tillers.Data are taken at the Institute during themain (wet) growing season, June-November.

The ratio of bearing tillers to the totalnumber of tillers is also a varietal charac-.teristic.

e. Strength : Culm strength varies among va-rieties and also within a variety with chang-ing environments. This trait is first ratedfollowing panicle emergence by gently push-ing the tillers back and forth at a distanceof about 30 cm. from the ground. Thisbending test gives some indication of stiff-ness and resilience. Additional observationat maturity is made to record the standingposition of the plants. Upright plants areconsidered sturdy. If culms break readily,they are termed brittle. Plants with bend-ing or buckled culms are called weak or

lodged.

Detailed information on straw strength may beobtained by (i) mechanical culm breaking or pull-ing devices, (ii) a brass chain hanging from the

panicle base to give cLr (lodging resistance fac-tor) estimates, or (iii) P/E estimates (ratio ofcritical straw strength to the modulus of elasticity)derived from culm measurements (cf. IRRI 1964,Chang 1964b).

8. Nodal septum: The color of the septum isbest seen by slitting longitudinally the lower por-tion of the culm and examining the cut surface.Colors are light yellow, pink, and shades of purple.

9. Sheath pulvinus: The pulvinus can be color-less (white), green, shades of purple (includingred), or purple dots.

10. Stigma color: This is examined during an-thesis using a hand lens. Colors are colorless,yellow, light purple, or purple.

11. Sterile lemmas (recorded as the terminalspikelets start maturing) :

a. Color: colorless (white), straw, gold,brown, red or purple.

b. Length: short (less than one-third of lem-ma), long (more than one-third), or extralong (longer than lemma) ; nearly equal orunequal (one-sided) in length.

12. Lemma and palea:

a. Color at anthesis: green, pale yellowishgreen, gold, blackish brown furrows, shadesof purple (purple tips, purple spread, or full

purple), piebald and mottled patterns.b. Color at maturity: White, straw, tawny

(light to dark brown), gold, brown furrows,

brown spots (piebald), russet, reddisbrown, shades of purple, or sooty blacColor illustrations have been given by Huchinson et al. (1938), Ramiah and Ra(1953), Takahashi (1957), and Ghose et a(1960).

c. Pubescence : glabrous or pubescent ; short olong trichomes (indicate the length andensity of trichomes and specific areas o

measurement).d. Phenol staining: Grains are soaked in 1

percent aqueous phenol solution for 2hours, drained and air-dried. Hull color then recorded : unstained, entirely stain(dark brown), or partly stained.

13. Apiculus (examined first during anthesand then at maturity) :

a. Color at anthesis : straw white, seashepink, rose red, tyrian rose, pomegranapurple, amaranth purple, pansy purple, anblackish red purple. Color plates have beegiven by Takahashi (1957).

b. Color at ripening: white, straw white, warbuff, ochraceous-buff, tawny (light to dabrown), russet, faded pink, faded red purpland faded purple. Color plates have beegiven by Takahashi (1957).

c . Pubescence : glabrous or pubescent (indicalength and density).

14. Awn (recorded as the terminal spikelestart maturing)

a. Presence ;(i) Fully awned: all spikelets on th

panicles are awned: but awns ofte

vary in length.(ii) Partly owned : awned and awnlespikelets are present on the sam

panicle.(iii) Terminally awned: short awns a

present on spikelets near the tip of thpanicle branches.

(iv) Awnless: awns are absent and do ndevelop under any condition.

b. Length: long, medium, short, or tip awnc. Color: colorless (white), straw, gold, brow

15. Rachilla: May be cup-like, elbow-like,

16. Panicle:

a. Type: open, compact, or intermediate.b. Length: measured from the panicle bas

c. Angle of primary branches: erect, droopin

d. Form: equilateral (paired branching) o

pink, red, purple, or black.

comma-like.

to the tip.

or intermediate.

unilateral (one-sided branching).

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e. Density (number of spikelets per unit lengthof panicle) : dense, lax, and intermediate.

f. Clustering: in most varieties, the spikeletsare evenly distributed along the primary orsecondary branches. Occasionally, somevarieties have two or more spikelets clus-tered on the panicle branches at irregularintervals. The degree of clustering variesfrom 2 to as many as 48 on a secondary

branch.

g . Exsertion :

(i) Exserted (panicle base is clearly abovethe flag leaf sheath).

(ii) Partly exserted (panicle base appearsat the same level as the top of the flagleaf sheath).

(iii) Partly enclosed (panicle is partly en-closed by the flag leaf sheath).

(iv) Enclosed (panicle is entirely enclosedby the flag leaf sheath).

h. Shattering: Tight, intermediate, or shatter-ing. Shattering can be measured in the fieldby gently grasping by hand the maturepanicle and applying a slight rolling pres-sure. Ratings are:

(i) Tight.: few or no grains removed.(ii) Intermediate: 25-50 percent of grains

(iii) Shattering: more than 50 percent of

Shattering can also be determined in the labor-atory by rolling a weighted cylinder (about 1 kg.)several times over panicle samples placed on a flator inclined board and counting the percentage ofdropped grains.

i . Weight (of panicles on the main culm driedto 13 percent moisture content of grains).

17. Maturity: Maturity is computed in daysfrom seeding to ripening of more than 80 percentof the grains on the panicle. Another commonlyused measure is the date of panicle emergence(heading). Days from sowing to 5 percent emer-gence of all panicles in a plot may be called daysto first heading; 60 percent emergence of all

panicles, middle heading: and more than 90 percentemergence of all panicles, full heading.

For tropical varieties, the following maturityranges are applicable: 100 or less, 101-115, 116-130,131-145, 146-160, 161-176, 176-190, 191-205, and206 or more.

The total growth duration of a rice varietygenerally may be resolved into 4 components:(a) basic vegetative phase, (b) photoperiod-sensitive phase, (c) thermosensitive phase, and(d) reproductive phase from panicle initiation tomaturity. Among photoperiod-sensitive genotypes

removed.

grains removed.

of diverse geographic origin, varieties often differin the optimum photoperiod at which the panicle-initiation process is critically affected. Therefore,the growth duration of a photoperiod-sensitivevariety at a given location or latitude is determined

by the optimum photoperiod of the variety and thedates on which the critical photoperiod prevails atthat latitude. Consequently, different plantingdates usually affect the total growth duration.

Presently, no standard methods are availableto evaluate readily the photoperiod response orthermosensitivity of many varieties. However, ifduplicate plantings are made during different sea-sons, information on photoperiod sensitivity and/orthermosensitivity may be obtained, When photo-

period chambers are available, two controlled photo-periods (10 hr. and 16 hr. of light) would differen-tiate most varieties. A photoperiod-insensitivevariety would initiate panicles under the 16-hourphotoperiod (or comparable, natural long-day con-ditions) with a duration comparable to or not morethan 10 days longer than that grown under the10-hour treatment (or comparable, natural short-day conditions). Varieties showing a difference of10-20 days in heading date may be classified asweakly photoperiod-sensitive: those with a differ-ence longer than 20 days are definitely photoperiod-sensitive. The effect of thermosensitivity ongrowth duration is generally less than that of

photoperiod sensitivity, especially in the tropics.

Formulas for estimating photoperiod sensitivityhave been given by Chandraratna (1966, 1966),Oka (1954), and Katayama (1964).

Varieties also differ in the duration from an-thesis to full maturity. The duration of graindevelopment generally varies from 25 to 40 days.

18. Plant height: Measured on the main culm(or the tallest tiller) at or following anthesis fromground level to the tip of the panicle. Plantingmost of the photoperiod-sensitive varieties undershort-day length would result in fewer tillers,shorter plants, and earlier maturity. At the Insti-tute, plant height and other quantitative traits aremeasured in the main (wet) season, June-Novem-

ber.

19. Internode elongation pattern: Plant heightis largely the summation of elongated internodes(including the panicle axis) on the culm. Ricevarieties generally have 12 to 22 internodes, ofwhich 4 to 9 are elongated 5 cm. or longer. The

number and individual length of elongated inter-nodes are characteristic of a certain variety undera given environment and are often associated withgrowth duration (cf. Guevarra and Chang 1965).Internode elongation patterns represented by ideo-grams or internode length/culm length ratios forspecific internodes facilitate comparison of varie-ties under identical or different treatments (IRRI

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1964, 1966 ; Guevarra and Chang. 1966).

20. Photosynthetic leaves at maturity: Thischaracteristic is not commonly reported but may

prove. useful to rice agronomists and breeders. Itmay be expressed as a ratio of photosyntheticleaves to the total number of leaves on the culm.

a. Photosynthesis: leaves retain their green

b . Dead : leaves become non-functional even

color when panicles ripen.

before the grains are fully mature.

21. Spikilet or pollen fertility: The mean per-centage of fertility is obtained from the percentageof welldeveloped spikelets (or pollen grains) in the

panicle and sampled from a number of panicles inthe plot.

Percentage of fertility Classification

more than 90 highly fertile75-90 fertile50-74 partly sterile10-49 sterile

less than 10 highly sterile

22. Grain dimensions, shape and weight:

a) Length. (mm.) : longitudinal dimensionmeasured from 10 well-developed grains asthe distance from the base of the lowermoststerile lemma to the tip (apiculus) of thelemma or pales, whichever is longer. In thecase of awned varieties, length is measuredto a point comparable to the tip of the api-culm (Fig. 7). A photo-enlarger with acalibrated easel is used at the Institute forthe above classification.

b) Width (mm.) : dorsiventral diameter mess-ured from 10 grains as the distance acrossthe lemma and-the palea at the widest point(Fig. 7).

c) Thickness (mm.) : lateral diameter meas-ured from 10 grains as the largest distancebetween' the two lateral sides in the middlepart of the caryopsis. A screw micrometeror a dial-type vernier caliper is used.

d) Shape: generally expressed as a ratio, be-tween length and width.

e) Weight: measured from 100 grains dried to13 percent moisture. Seven grain weightclasses are given by FAO . Volumetricweight such as test weight or liter weightis another useful varietal characteristic.

23. Hull percentage: Hulls are readily removedin a sheller or dehuller. The proportion of hull tograin (rough rice) on a weight basis is anotheruseful varietal characteristic. Hull percentage mayvary from 16 to 35 percent among varieties. Thecomplement of hull percentage is the percentageof brown rice.

Fig. 7. Length and width measures of the grain.

24. Dimensions, shape, and weight of browor milled rice: The size, shape, and 100-kernweight of brown or milled rice are additional cteria for identifying varieties.

Two ,classification schemes that have been su

Size (length) USDA scale FAO scale

gested are as follows:

for milled rice4 for milled ric

Extra long

LongMedium or

middlingShort

more than7.60 mm.

6.61-7.50 mm.

5.51-6.60 mm.less than

5.51 mm.

more than7 mm.

6.0-7.0 mm.

5.0-6.9 mm.less than

6 mm.

Shape (length/ USDA scale FAO scale fowidth ratio) for milled rice brown ria

SlenderMediumBoldRound

more than 3.02.1-3.0

less than 2.1-

more than 32.4-3.02.0-2.39

less than 2

4 Unofficial scale used by USDA rice researchers ais not the basis for official USDA marketing classes.

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25. Pericarp and tegmen color: The color ofbrown rice is determined by pigments in the peri-carp and tegmen. The starchy endosperm of allrice varieties is white. Pericarp and tegmen colorsinclude white, light red, red, reddish brown, brown,grayish brown, golden, reddish purple, and fullpurple (almost black).

26. Amylopectin/amylose ratio in starchy en-dosperm : The amylopectin, amylose ratio expresses

the relative proportion of each type of starch inthe endosperm.

a. Waxy or glutinous: brownish staining re-action with weak potassium iodide-iodinesolution, indicating that only amylopectin ispresent in the starch granules. Potassiumiodide-iodine solution is prepared by dis-solving 1 g. of potassium iodide and 0.3 g.of iodine in 100 ml. water.

b. Non-waxy or non-glutinous, common : darkblue staining reaction with potassiumiodide-iodine solution, indicating the pres-ence of amylose in the starch granules.

27. Embryo size: Small, medium, large.28. Physical features of milled rice:

a. Shape: No standard measures are availablefor tropical varieties. Commonly used de-signations are slender (fine). medium, bold(coarse), round, and flat.

b. Translucency : translucent, opaque, and in-termediate.

c. Size: Whole kernels and broken pieces maybe separated by a sizing device and ex-pressed as a ratio or percentage.

d. Chalky spots: white belly, white core, andwhite back.

e. Hardness: determined by a grain hardnesstester as g./mm.2

f. Weight: 3 weight classes are given by FAOfor 1,000-kernel weight of milled rice -very large (more than 28 g.) , large (22 to28 g.), and small (less than 22 g.) .

29. Chemical properties of starchy endospermrelated to cooking characteristics: Among rice va-rieties, grain size and shape are generally asso-ciated with certain cooking and processing char-acteristics. Most long-grain Varieties tend to be-come dry and fluffy when cooked and the cookedkernels do not split or stick together. Short-grainvarieties are usually more cohesive and firm than

long-grain varieties. Medium-grain varieties havegenerally intermediate features. There are manyexceptions to this classification.

The differences in cooking and processing be-havior are largely due to inherent differences inthe chemical make-up of the starchy endospermrather than to grain size and shape. Some of theinherent varietal quality differences are given be-

low. Environmental factors such as temperature,light, nitrogen supply, and storage conditions alsoaffect the cooking behavior.

a) Amylose content: High amylose content isassociated with the dry, fluffy cookingfeatures. Amylose content may be deter-mined analytically (Williams et al. 1958) orestimated by the starch-iodine-blue test(Halick and Keneaster 1956).

b) Gelatinization temperature : Gelatinizationtemperature indicates the temperature atwhich starch granules swell irreversibly inwater with a simultaneous loss of bire-fringence. It may be estimated by soakingmilled rice for 23 hours in a weak alkali so-lution at 30C. The extent of endospermdisintegration gives an estimate of relativegelatinization temperature. Alkali-resistantsamples indicate high gelatinization temper-ature. Three classes are generally recog-nized: low (62-69), intermediate (70-74), and high (75-80). Gelatinizationtemperature also may be estimated by the

amylograph test, the granule-swelling meth-od, and the loss of birefringence of starchunder a polarizing microscope. Amylose con-tent and gelatinization temperature appearto be genetically independent (Beachell andStansel 1963, Juliano et al. 1964).

c) Pasting viscosity: The difference ("set-back") between peak viscosity of hot-paste(95C.) and cooled paste (50C.) measuredwith an amylograph suggests certain par-

boiling and canning characteristics of ricesamples (Halick and Kelly 1959). Pastingviscosity is affected by amylose content and

protein content.

d) Protein content: The exact role of proteincontent in determining cooking quality is notwell understood but it is known to be affect-ed by environmental and nutritional condi-tions under which the crop is grown. Proteincontent is determined by analytical methods.

e) Aroma: scented or non-scented. Whether avariety is scented or not may be detectedduring anthesis, milling and/or cooking. Theidentity of the volatile chemical (s) inscented rice has not been determined.

30. Resistance to diseases and insects: Rice va-rieties differ in their reaction to a specific patho-gen or insect pest. Known examples include rice

blast, bacterial leaf blight, bacterial streak, Hel-minthosporium leaf spot, Cercospora leaf spat,

culm rot, sheath blight, rice stunt and other virusdiseases, Rhizoctonia seedling blight, Fusariumseedling blight, white-tip disease (nematodes),leaf-hoppers, stem maggots, and the stem borers.

Varieties can be further differentiated in theirreaction to specific pathogenic or physiologic races

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of one pathogen. Well known samples are specificvarietal reactions to different races of the blastfungus. In other staple cereals, pure isolates ofthe rust fungi are sometimes used as a tool in puri-fying a breeders seed of commercial varieties.

31 . Reaction to physiological diseases. Rice va-rieties also differ in their reaction to certain phy-siological disturbances. Known examples are dif-ferences in varietal resistance to straight headwhich is largely caused by prolonged flooding ofsome soils. Other examples are physiological di-seases such as Akiochi and Akagare caused bya deficiency in certain nutrient elements and/or anexcess of harmful products of extreme soil reduc-tion.

32. Cultural adaptation: Rice culture is gen-erally divided into lowland and upland culture. Low-land culture refers to continuous flooding of thefields except for occasional drainage, i.e., controlledirrigation. But upland culture embraces a contin-uous range from the strictly non-irrigated, upland

type of cropping in Japan and certain parts of westAfrica to the rain-fed upland fields of the tropicswhere the rice plant grows in flooded soil for a sub-stantial portion of its life cycle. In the tropics anupland field means that either the field is ele-vated ground which gravity-fed irrigation sys-tem cannot reach and where water-retaining de-vices are not available, or is low-lying withoutadequate irrigation facilities. Yields from uplandfields are generally lower than those from lowlandfields.

Experiments have shown that most of the so-called upland tropical varieties gave higher yields

when grown under irrigated conditions than undera natural, haphazard type of intermittent flooding.Some of the upland varieties yielded as high asor even higher than certain lowland varieties whengrown under flooded conditions. Designating a va-riety as upland is not necessarily related to the re-sistance to drought of the variety either in theseedling or the adult stage.

A number of the so-called upland varietiesgrown in the tropics have the following character-istics in common: (1) rapid emergence from thesoil following direct seeding, (2) vigorous seedlinggrowth to compete with weed growth, (3) low tomedium tillering ability, (4) non-sensitive or weak-

ly sensitive to photoperiod, and (6) maturityranges of 100 to 150 days.

No clearcut morphological or physiological cri-teria are yet available to differentiate rice varietiesinto lowland and upland types, although such termsare widely used as cultural designations.

In many river deltas of tropical Asia, rapidlyrising water levels during the peak of the monsoonseason permit only the growing of the floating va-

rieties. Floating varieties are generally describas long duration (160-240 days), photoperisensitive varieties with many internodes which celongate rapidly to cope with rapid increases water level. They are known to withstand 5 tometers of standing water. There is also a groof varieties intermediate between the common, nofloating varieties and the fioating varieties. Cal

deep-water varieties, they can stand 2 to meters of water without obvious adverse effec

The term saline-resistant or saline-tolerant rieties has been used to denote varieties than ctolerate salinity levels between 0.5 percent a1.0 percent and still produce a fair yield of graAgain, simple and reliable .tests for resistance salinity need to be formulated.

Varieties also differ markedly in tolerance low air temperatures and strong air movemshortly after seedling emergence from the sThese differences are crucial in sub-tropical atemperate regions where rice is sown early in

year. As a general rule, the temperate zone ponica varieties are more tolerant than the tropiindicas.

At high latitudes, low air temperatures durthe period between panicle development and polfertilization cause high sterility. Heritable diffences among Japanese varieties have been obtainto facilitate selection for more tolerant strains

Irrigation water of low temperature readinearly in the planting season has caused severe mtality to rice seedlings in California and HokkaiThere is sufficient varietal diversity to enable rbreeders to select cold-water resistant strains.

33. Seasonal adaptation : Rice varieties of Inand Pakistan are divided into autumn, winspring, and summer varieties on the basis of harvest season. Other classification schem

based on growing period are : main and off seasonearly, medium, and late seasons; first and secoseasons ; and wet and dry seasons.

Experiments have shown that the above disions were based largely on photoperiod sensitivand thermosensitivity. As mentioned before, vrietal differentiation based on specific physiologicharacters is preferred to cultural designation.

34. Ratooning ability: Rice varieties differ ratooning ability following initial harvest. But tention must be given to uniformity in cultufactors such as water and nutrient supply whcomparing varietal differences in ratooning abili

35. Yield and yield components: The three bsic physical components of grain yield per unit arare (a) the number of panicles per unit area, (the number of welldeveloped grains per panicand (c) grain weight. Under comparable grow

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nditions, each variety shows a fairly consistentomposition of grain yield in terms of the threeomponents. Rice varieties have been divided intoree groups on the above basis : (a) panicle-eight or heavy-eared type (large and heavyanicles, few panicles per plant), (b) panicle-umber or many-eared type (small and lightanicles, many panicles per plant), and (c) an in-rmediate type.

Grain yielding ability is also used as a varietalharacteristic. When used as such, plot yield isore meaningful than single-plant yield. Graineld data supplemented by data on the three com-

onents provide more information for comparativediagnostic studies.

The grain/straw weight ratio is another cri-rion which has shown relatively high consistency

certain varieties and may therefore be used asn additional basis for varietal differentiation.

36. Geographic designation : Since two hundredC., rice varieties of China were recorded underree groups: hsien, kng, and glutinous. In928

-1930, Japanese workers (Kato et al. 1928)

vided cultivated rice into two subspecies, indi- and japonica, on the basis of geographicalstribution, plant and grain morphology, hybriderility, and serological reaction. The indica group= hsien) included varieties from Ceylon, south-n and central China, India, Java, Pakistan, Phil-pines, Taiwan, and other, tropical areas, wherease japonica group (= kng) consisted of varie-es from northern and eastern China, Japan andorea. Japanese workers (Matsuo 1952, Oka 1958,

Morinaga 1954, Morinaga and Kuriyama 1958)ter added a third group, javanica, to designatee bulu and gundil varieties of Indonesia.

The above three groups and their general mor-hological and physiological features are sum-arized as follows :

INDICABroad, light-green leaves

Slender, some-what flat grains

Profuse tilleringTall plant stature

Mostly awnless

Thin and shorthairs on lemmaand palea

Easy shatteringSoft plant tis-sues

Varying sensitiv-ity to photoper-iod

JAPONICANarrow, dark

green leavesShort, roundishgrains

Medium tilleringShort plant sta-ture

Awnless to longawned

Dense and longhairs on lemmaand palea

Low shatteringHard plant tis-sues

Varying sensitiv-ity to photo-period

JAVANICABroad, stiff, lightgreen leaves

Broad, thickgrains

Low tilleringTall plant stature

Awnless or longawned

Long hairs onlemma and pa-lea

Low shatteringHard plant tis-

Low sensitivity tosues

photoperiod

Other criteria used by Japaneee workers toclassify varieties are endosperm characteristics,physiologicaI characters of germinating seedlingsand adult plants, phenol staining of hulls, resist-ance of seedlings to KClO3 toxicity, and seedlingreaction to organo-mercuric compounds.

Later studies with larger collections of varietiesshowed that the morphological and physiological

variations among the three geographic groups werelargely continuous, and the phenomenon of inter-varietal hybrid sterility was much more complicat-ed than a simple classification of three groups.

Therefore, the above scheme of dividing ricevarieties into geographic races is rapidly losing itssignificance. Varieties which fall into the japonicagroup have been isolated in semi-wild conditionsfrom Nepal, Ceylon, the Jeypore Tract of OrissaState in India, and northern Thailand. Hybridiza-tion on a wide genetic basis has further confusedthe classification scheme. This is particularly truewith U.S. and Taiwan varieties developed in recentyears.

Despite these shortcomings, the terms indica,japonica, and javanica are often used by ricescientists in Asia as convenient designations toindicate different plant and grain types.

37. Other tests of potential value: In additionto the above methods and criteria, several otherswhich show promise in differentiating varieties arecited below :

a. Spodogram analysis: The shape, density,and distribution of silica cells in the epider-mal tissues of blades and leaf sheath arehighly characteristic of certain varieties.

b. Grain (seed) dormancy: Germination testsof freshly harvested panicles, air-dried toabout 14 percent moisture, will give an indi-cation of dormancy. Varieties differ in theduration and intensity of dormancy (Jen-nings and de Jesus 1964).

c. Leaf characters: Varieties differ in leaf di-mensions, density and arrangement. The leafarea index (LAI) of the blades is highlycharacteristic of a variety when grown un-der a given set of environmental condition8and is useful in comparing the efficiency ofleaves in utilizing sunlight. Other criteriarelated to leaf area index and useful in dif-

ferentiating varieties are the light transmis-sion rate (I/I0) and the extinction coeffi-cient (K). Among the three, the light trans-mission rate is the most readily measurablecriterion (cf. Hayashi and Ito 1962, IRRI1964, Tanaka et al. 1964).

d. Numerical symbolization of pigmentation inplant parts : In view of the complexity of theanthocyanin distribution among plant parteand the various properties of color expres-

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sion (hue, value, and chroma), Ito and Aki-hama (1962) suggested the use of a numer-ical scale to combine recordings of the hue,value and chroma in 5 selected plant parts,using the Munsell color charts. An extensionof this scheme may facilitate the card ca-taloging of varieties.

e. Protein fractions of plant tissues: Studies

at the Institute have shown that certain in-dica and japonica varieties differ in the pro-tein fractions of leaf tissues (IRRI 1964).They also indicated that the greenness ofleaves is correlated with nitrogen respon-siveness and chlorophyll content (Tanakaet al. 1964). Other aspects of chemical planttaxonomy have been discussed in a sympo-sium on the subject (Swain 1963).

f. Statistical approach to varietal classifica-tion: When a number of taxonomic unitsof either a quantitative or codable natureare recorded, a variety of multivariate-analysis techniques are now available to as-

sist in evaluating similarities between taxo-

nomic units and the ordering of these unitsinto groups on that basis. Principles andtechniques have been given by Sokal andSneath (1963).

Classification of CultivatedVarieties of O. Sativa

The great majority of the classification schemesfound in the literature emphasize varietal differ-ences of a regional scope (cf. Grist 1959, Chan-draratna 1964) and therefore have limited appli-cation. This is illustrated by Beales (1927) classi-

fication of rice varieties from lower Burma inwhich five major groups were recognized on thebasis of grain length and the length/width ratio,supplemented by similar measurements of the de-hulled grain. Beale further subdivided each groupinto seven classes on the basis of pigments in thestigma, apiculus, leaf axil, leaf sheath, and the

blade. The 35 combinations supposedly embracedthe total varietal diversity in Burmese rice. In ad-dition to anthocyanin pigmentation and grain di-mensions, the presence or absence of awns, the na-ture of the starchy endosperm, the arrangement

of spikelets on the panicle branches, the size anshape of the sterile lemmas, the pubescence of thlemma and palea, and the form of spikelet separation from the pedicel were the criteria used in otheclassification schemes.

Since 1950, the Food and Agriculture Organization of the United Nations has published a Worl

Catalogue of Genetic Stocks (Rice), totaling 1issues, in which available informatior, was given oas many as 78 items for each variety. This hahelped rice workers select and exchange expermental materials. However, the information on individual varieties is based on data furnished b

breeders in the varietys home country. Consequently, some of the quantitative data have limiteapplicability when the variety concerned is growunder a markedly different set of environmentconditions. This is particularly true with varietieof the temperate zone when grown in tropical areaunder cultural practices adapted to the profustillering tropical varieties.

While none of the presently available classifcation schemes is entirely satisfactory for the thousands of rice varieties under cultivation and probably none will ever serve the needs of all interesed workers, a centralized agency is needed to wortoward planting, recording and cataloging existincommercial varieties for morphological and agronmic characteristics under a uniform set of condtions and to preserve the valuable germ plasmwhen the existing stock of varietal diversity ra

pidly dwindles. The world collection of the Instituis being investigated and maintained in the abovmanner to meet this need. But the task of continuously developing identification and classifica

tion schemes for commercially important varietieof a country or region should be largely the reponsibility of national governments concernesince it is impossible for one agency to develop catalog that would contain all of the informatiodesired by various workers and which would alsapply to all of the varieties when grown at different locations. Therefore, international and inteagency cooperation is needed to pool all availabinformation on cultivated varieties in a form thwould be readily accessible to all interested workers.

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MUTANT TRAITS

mutant trait is defined as a variant that is rela-A tively discrete from the normal or parental typeand is inherited in a simple Mendelian manner. Thenormal type refers to that of the great majorityof cultivated varieties. Thus, the mutant traits arevariants of a more extreme nature than those com-monly observed in a small group of commercialvarieties.

A wide array of mutant traits has been report-ed in rice. The more commonly observed ones arereviewed under eight convenient groupings. Defi-nitions of specific mutant traits and assignment ofthe IRC-recommended gene symbols are given inthe attached glossary. Genetic information on othermutants of a more exotic nature have been given

by Jones (1933), Nagao (1951), Ramiah and Rao(1953), Jodon (1957), Nagai (1958), Ghose, Ghatgeand Subrahmanyan (1960), and Chandraratna(1964). Recent tabulations on gene symbols, gen-etic ratios and authors are given in two IRC reports(Anon. 1963, Chang and Jodon 1963).

Variations in AnthocyaninPigmentation

The plant parts which may be pigmented withanthocyanin are the apiculus, auricles, awn, blade,coleoptile, collar (junctura), hull (lemma and pa-lea), internode, leaf axil (inner sheath base), leafsheath, sheath pulvinus, leaf tip and margin, li-gule, midrib, nodal septum, pericarp, tegmen, ste-rile lemmas, and stigma. The color variations arecolorless (white), green, pink, red, and severalshades of purple.

The genes controlling anthocyanin pigmentationare basically three complementary genes: C5, A,

and P6. C is the basic gene for producing chro-

5 Letters in italics are IRC-recommended gene symbols(cf. Anon. 1959, Anon. 1963, Chang and Jodon 1963).

6 P, when used as the first letter of a gene symbol,denotes anthocyanin color in a certain plant organ or or-gans; exceptions: Ph, Pi. Examples are P for apiculus, Paufor auricles, Pin for internode, Pl for leaf blade, Prp forpericarp, Psh for leaf sheath, Ps for stigma, and Px forleaf axil.

mogen. A controls the conversion of chromagen ianthocyanin, and P controls the distribution or calization of anthocyanin in specific plant organ organs. C and A are genes with multiple allelic ries. Some of the P genes also have several allelex., Pl, Plw and Plt. Inhibitor genes (I-)known to suppress the effect of the distribut

genes, e.g., I-P, I

-

Pl, and I-Pla. Through the intaction of the above genes, a great variety of coexpressions and intensities are observed in natu

The P and Pl alleles also have a pleiotropic fect upon the pigmentation of the other plant gans.

Red pericarp and tegmen (red rice) is controlby two complementary genes, Rc and Rd. When alone is present, the color of the caryopsis is spkled reddish-brown.

Colors for the above have been designated

Hutchinson et al. (1938), Ramiah and Rao (195Takahashi (1957). and Ghose et al. (1960).

Variations in Non-AnthocyaninPigmentation

The coloration of plant parts such as gobrown, and sooty black does not involve anthoanin. Non-anthocyanin pigmentation generally volves a single pair or a series of alleles, such asalleles for brown furrows on hull at maturity, genes for black hull, gh for gold hull, H alleles

dark brown furrows on hull at blooming, andfor white hull. Inhibitor genes such as I-Bf and Ihave been reported.

Modifications in Size and ShapeA common modification in size is dwarf stat

which is about one-third to one-half the heightnormal plants. Dwarf plants form discrete clasin segregating generations and are characteri

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by under-sized grains and proportionally thickenedplant parts. A number of independent, recessivegenes (d1, d2. . . ) of a pleiotropic nature controlthe dwarfed growth. These single-recessive dwarfshave no economic value in a breeding program.

Plants of intermediate (sub-normal) heightwith normal panicles and grains may be calledshort or semi-dwarf plants. The short (circa 100em.), nitrogen-responsive and high yielding indicavarieties from Taiwan, viz., Taichung (Native) 1,I-geo-tze and Dee-geo-woo-gen, belong to this class.Differences in plant stature between the tall tro-pical varieties and these short varieties are con-trolled by a partially dominant allele and a few mo-difying genes (Chang et d. 1965). In others cases,an inhibitor for tall plant height (I-T) may be in-volved.

Other simply inherited differences in size andshape involve grain length( lk alleles. for long),grain shape (Rk for roundness), sterile lemmalength (g, or Gm for long), blade width (nal for

narrow blade), and panicle length. Some of theabove variations in size and shape are probablymore of a quantitative nature.

Presence or Absence of StructuresThe presence or absence of awns, auricles, col-

lar, ligule, neckleaf, and pubescence generally in-volves differences in one allele. The. presence of acertain structure is generally controlled by the do-minant allele, such as An for awned, Lg for liguled,anti Gl for pubescence. The presence or absenceof the ligule, auricles, and collar is generally in-

herited as a unit (Lg vs. lg) in a pleiotropic man-ner.

Modifications in Structure

Marked variations in the structural features ofplant organs include rolled leaf (rl), twisted leaf(tl) , glossy leaves, bend node (bn) , lazy (la),non-exserted panicle (ex), sinuous neck (sn), un-dulate rachis on the lower panicle branches (Ur),verticillate rachis (ri), spreading panicle branches(spr) , lax panicle (dn), clustering of spikelets onthe panicle branches (Cl) , cleistogamous spikelets

(cls) , claw-shaped spikelets (clw) , triangular hull

(tl-i) , extra lemma (lmx) , double awn (da), de-pressed palea (Dp), beaked hull (Bd), open hull(o), shattering (Sh or th), multiple pistil (mp),

poly-embryonic grain (me), and notched or twist-ed kernel (nk or tk). Although some of the abovetraits, such as panicle density and shattering, weredescribed as simple Mendelian characters they are

probably polygenic in inheritance.

Modifications in ChemicalComposition

Some of the simple modifications in chemicalconstitution of plant parts are extremely brittleculm and leaves (bc), fragrant flower (fgr), scent-ed endosperm (Sk1. Sk2. . . ), waxy endosperm(wx), translucency and chalkiness of the starchy

endosperm (wb, wc) , and phenol staining of hulls(Ph). Pigmentation, chlorophyll deficiencies,growth habit, and other physiological charactersmentioned in preceding sections also involve modi-fications in the chemical composition of the plantorgan or tissues.

Modifications in Growth HabitSome of the well-known modifications in growth

habit are erect (er) vs. spreading, erect vs. lazy orageotropic growth (la), floating vs. non-floatinggrowth (Dw1, Dw2), and differences in ratooningability. These differences in growth habit also are

known to be controlled by specific chemicals (hor-mones or growth substances).

Modifications in OtherPhysiological Characters

Other well-known modifications in physiologicalcharacters involve a complex of chlorophyll defi-ciencies, leaf discolorations, variations in maturityor photoperiod sensitivity, gametic and zygoticsterility, variations in grain dormancy, and resist-ance to specific diseases and insects.

Chlorophyll deficiencies occur in a variety of

expressions. Albino (al) , xantha (I-

y) , lutescent(lu) , and tip-burn yellow (tb) are lethal types andare detectable immediately following seedling emer-gence Chlorina (chl) . pale yellow (y), zebra stripe(z), green and white stripes (fs or gw), and vi-rescent (v) are non-lethal and the seedlings usual-ly regain the green color later in growth. Whitestreaks or stripes (ws) may also be found on theblade, leaf sheath, culm, and spikelets persistingthr

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