Oryza (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Oryza L.

Protologue: Sp. pl.: 54 (1753), Gen. pl. ed. 5: 29 (1754).

Family: Gramineae

Chromosome number: x= 12; 2n= 24 (O. australiensis, EE group; O. granulata;O. meridionalis, AA group; O. meyeriana; O. nivara, AA group; O. officinalis, CC group; O. rufipogon, AA group; O. sativa, AA group); 2n= 48 (O. longiglumis; O. minuta, BBCC group; O. ridleyi, O. schlechteri).

Major species and synonyms

• Oryza australiensis Domin, Bibl. bot. 85(1): 333 (1915).

• Oryza granulata Nees & Arnott ex Watt, Dict. econ. prod. ind. 5: 500 (1891), synonyms: O. meyeriana (Zoll. & Mor.) Baillon subsp. granulata (Nees & Arnott ex Watt) Tateoka (1962) and var. granulata (Nees & Arnott ex Watt) Duistermaat (1987).

• Oryza longiglumis Jansen, Reinwardtia 2: 312 (1953).

• Oryza meridionalis Ng, Bot. J. Linn. Soc. 82: 328 (1981).

• Oryza meyeriana (Zoll. & Mor.) Baillon, Hist. pl. 12: 166 (1894), synonyms: O. abromeitiana Prodoehl (1922), O. meyeriana (Zoll. & Mor.) Baillon subsp. abromeitiana (Prodoehl) Tateoka (1962), subsp. meyeriana [Tateoka] (1962) and var. meyeriana [(Tateoka) Duistermaat] (1987).

• Oryza minuta J.S. Presl, Rel. Haenk. 1: 208 (1830), synonyms: O. manilensis Merrill (1908), O. latifolia auct., non Desv.

• Oryza nivara Sharma & Shastry, Ind. J. Gen. Pl. Br. 25: 157 (1965).

• Oryza officinalis Wallich ex Watt, Dict. econ. prod. 5: 501 (1891), synonyms: O. latifolia Desv. var. silvatica Camus, O. malampuzhaensis Krishn. & Chandr. (1958).

• Oryza ridleyi Hook.f., Fl. Br. Ind. 7: 93 (1896), synonym: O. stenothyrsus K. Schum. (1905).

• Oryza rufipogon Griffith, Notul. pl. Asia 3: 5 (1851), synonyms: O. fatua Koenig ex Trin. (1839), O. sativa L. f. spontanea Backer (1928) & f. spontanea Rosh. (1931), O. aquatica Rosh. (1937).

• Oryza sativa L. - see separate article.

• Oryza schlechteri Pilger, Bot. Jahrb. 52: 168 (1915).

Vernacular names

For general rice names, see Oryza sativa L. article.

O. granulata:

• Jungle oryza (En)
• Indonesia: rumput lorodan, lorodan pari (Javanese)
• Thailand: khao-nok (south-western)
• Vietnam: lúa con cong.

O. meyeriana:

• Indonesia: hehawa (Sulawesi), padi-padian (Kalimantan)
• Philippines: paray-agway.

O. minuta:

• Indonesia: padi monyet (North Sumatra), paparean (Sundanese), suket paren (Javanese)
• Malaysia: padi burung
• Philippines: palay-maya (Sulu), bayli-gadja (Tausug), palai-palai (Subanun)
• Vietnam: lúa ma.

O. ridleyi:

• Malaysia: paroi tasur (Sabah)
• Thailand: ya-khaotham (south-eastern)
• Vietnam: lúa rừng.

O. rufipogon: Indonesia: padi burung (Sumatra), paparean (Java), waiwi (Irian Jaya)

• Malaysia: padi hantu (Peninsular)
• Vietnam: lúa hoang.

Origin and geographic distribution

There are strong indications that the genus Oryza originated in the Gondwana supercontinent, which began to fracture and drift apart in the early Cretaceous period, and that wild species differentiated out of a common ancestor and became widely distributed in the humid tropics of Africa, South America, South and South-East Asia (including south-western and southern China), Oceania and Australia. However, there is no agreement as to what the common ancestor might have been or whether it still exists. Of the wild species in Asia, O. nivara and O. rufipogon are found mainly in the Asian mainland, O. granulata, O. meyeriana, O. officinalis, and O. ridleyi span both mainland and islands, O. longiglumis, O. minuta and O. schlechteri are confined to the islands. Australia has O. australiensis, O. meridionalis and O. rufipogon. In addition to the cultivated O. glaberrima Steudel, Africa has the wild species O. barthii A. Chev., O. brachyantha A. Chev. & Roehr., O. eichingeri A. Peter, O. longistaminata A. Chev. & Roehr. and O. punctata Kotschy ex Steudel. South America has O. alta Swallen, O. glumaepatula Steudel, O. grandiglumis (Doell) Prod. and O. latifolia Desv.

Parallel and independent evolutionary processes occurred in Asia and Africa following the sequence of wild perennial to wild annual to cultivated annual. The corresponding members for Asia are O. rufipogon (wild perennial), O. nivara (wild annual) and O. sativa (cultivated annual), for Africa they are O. longistaminata (wild perennial), O. barthii (wild annual) and O. glaberrima (cultivated annual). O. sativa is now cultivated pantropically, O. glaberrima only in West Africa. In Australia, Oceania and South America no cultivated annual has been developed from the wild species.

Uses

The most important use of wild rices is in breeding programmes to improve cultivated rice because they are a source of resistance to or tolerance of biotic and abiotic stresses. They are also valuable as food supplement (e.g. O. nivara in India and Sri Lanka) and as famine food when other crops fail, as a raw material for special liquors (China) and they often provide a good fodder. In many parts of South Asia, wild rice grain is used as an offering to deities in the temples and can command a high price in the market where it is sold during religious festivals. In Burma (Myanmar), O. officinalis is a kind of holy plant and is protected within sanctuaries of Buddhist temples. Some wild rices are also used medicinally (e.g. O. officinalis in China).

Production and international trade

Wild rices are only used locally. None of the species is found in large enough patches to be traded.

Properties

The chemical composition of the starch fractions of wild rices is essentially the same as in the cultigen O. sativa. The protein and amino acid contents are very variable but not outstanding.

The red pericarp present in nearly all wild species is favoured by ethnic tribes and some urban people as having nutritional increments or is used for decorative purpose during festivities. On the other hand, if found in commercial lots, the red seed-coat carried by primitive cultivars lowers the grade of milled rice.

Description

• Annual or perennial plants with erect or ascending culms.
• Leaves herbaceous, sheath terete with more or less distinct transverse veinlets, blade flat, linear to lanceolate.
• Inflorescence a panicle; spikelets laterally compressed, usually articulating above the glumes, 3-flowered, lower two florets sterile, upper one bisexual; glumes 2, reduced; sterile lemmas 2, subequal, 1-nerved; fertile lemma boat-shaped, 5-nerved, usually with apical awn; palea 3-nerved, usually mucronate; lodicules 2, anthers 6; ovary with 2 styles.
• Caryopsis laterally compressed, 2-ribbed, or cylindrical, tightly enveloped by lemma and palea.

• O. australiensis. Perennial, growing in tufts, stoloniferous; culm erect, 80-240 cm tall; ligule ovate-triangular to lanceolate, 4-8 mm × 2.5 mm; nodes glabrous; blade linear, 25-35 cm × 0.4-1.4 cm; panicle 18-50 cm long, axis increasingly hispid scabrous toward the tip, primary branches with slightly woolly pubescence at their base; pedicel covered with long glossy hairs; spikelet 6.5-8.4 mm × 2.25-3.1 mm; awn of fertile lemma 5-55 mm long; caryopsis 4.7-6.4 mm × 2-2.5 mm, brown to red-brown.

• O. granulata. Perennial, loosely tufted or stoloniferous; culm erect to ascending, 23-78 cm long; ligule collar-shaped, 0.5-2 mm long; nodes glabrous; blade lanceolate, 8-27 cm × 0.7-2 cm, dark green; panicle 4-15 cm long; spikelet 4.9-6.5 mm × 1.5-2.6 mm; glume surface granulate; sterile lemma up to 1.4 mm long; fertile lemma awnless; caryopsis 3.4-4.1 mm × 0.8-2 mm, brown.

• O. longiglumis. Perennial, forming tufts, not stoloniferous; culm erect, 85-120 cm long; sheath tight, ligule collar-shaped, 1 mm long; nodes glabrous; blade linear, 25-40 cm × 1 cm; panicle 28-30 cm long; spikelet obliquely to horizontally inserted on the pedicel, 7-8 mm × 1.8-2.3 mm; sterile lemma 0.8-1.6 times as long as the spikelet; awn of fertile lemma 12-25 mm long; caryopsis about 4 mm × 1 mm, brown.

• O. meridionalis. Annual or perennial, sometimes forming small tufts, not stoloniferous; culm erect to geniculate, 1-2 m long; sheath tight but lower ones slightly inflated, ligule ovate to linear-lanceolate, 13-25 mm × 4 mm; nodes glabrous; blade linear, 18-30 cm × 0.9-1.2 cm, scabrous above; panicle 11-24 cm long; spikelet 6.5-8.9 mm × 2.1-2.5 mm; sterile lemma 0.2-0.3 times as long as the spikelet; awn of fertile lemma 70-120 mm long; caryopsis 6-6.4 mm × 1.7-2 mm, red-brown.

• O. meyeriana. Perennial, loosely tufted or stoloniferous; culm erect to ascending, 23-78 cm long; ligule collar-shaped, 1-5 mm long; nodes glabrous; blade ovate-lanceolate to linear, 8-27 cm × 0.8-3.2 cm; panicle 4-15 cm long; spikelet 6.1-10.5 mm long, about 3-6.5 times as long as wide; glume surface granulate; sterile lemma up to 2.5 mm long; fertile lemma awnless; caryopsis 4.1-7.3 mm × 0.8-2 mm, brown.

• O. minuta. Perennial, tufted, stoloniferous; culm erect, 0.5-2.3 m long; sheath tight, lower ones slightly inflated; ligule collar-shaped to triangular 1-8 mm × 2-5 mm, glabrous or hairy; nodes glabrous; blade linear, 15-80 cm × 1-2 cm, glabrous or hairy; panicle 9-20 cm long with spreading branches; spikelet 3.7-4.7 mm long, narrower than 2 mm; sterile lemma up to 3.4 mm long; fertile lemma without or with up to 23 mm long awn; caryopsis 2.3-4.4 mm × 1.3-2.3 mm, orange-brown.

• O. nivara. Difficult to distinguish from O. sativa . Annual, not stoloniferous; culm semi-erect to decumbent; ligule 14-45 mm long; nodes glabrous; panicle less branched than in O. sativa ; spikelet 6-8.4 mm × 1.9-3.0 mm; fertile lemma with thick, 4-10 cm long awn; caryopsis deciduous at maturity and with strong seed dormancy.

• O. officinalis. Perennial, tufted, stoloniferous; culm erect to semi-erect, up to 2.3 m long; sheath tight, lower ones slightly inflated; ligule collar-shaped to triangular, 1-8 mm × 2-5 mm, glabrous or hairy; nodes glabrous; blade linear, 15-80 cm × 1-2 cm, glabrous or hairy; panicle up to 42 cm long, whorled at base; spikelet 4-6.4 mm long, wider than 2 mm; sterile lemma up to 3.4 mm long; fertile lemma without or with up to 23 mm long awn; caryopsis 2.3-4.4 mm × 1.3-2.3 mm, orange-brown.

• O. ridleyi. Perennial, tufted, stoloniferous; culm erect, up to 3 m long; sheath tight; auricles often present; ligule collar-shaped, deltoid to triangular, 2-5 mm × 2-4 mm, glabrous; nodes glabrous; blade linear, 21-42 cm × 1.2-2.4 cm, glabrous; panicle 15-40 cm long; spikelet 7.6-12.7 mm × 1.7-2.9 mm; sterile lemma up to 10.5 mm long; fertile lemma with 3-12 mm long awn; caryopsis 5.9-7 mm × 0.7-1 mm, brown.

• O. rufipogon. Perennial, tufted or stoloniferous, with adventitious roots; culm decumbent and floating or ascending to erect, 1-3 m long, with extravaginal branching at higher nodes; sheath tight, lower ones slightly inflated; ligule triangular, 9-38 mm × 5-8 mm, glabrous; nodes glabrous; blade linear, 27-60 cm × 0.7-2.5 cm, glabrous; panicle 12-30 cm long; spikelet 7.3-11.4 mm × 2-4.4 mm; sterile lemma up to 7.5 mm long; awn of fertile lemma very variable, up to 11 cm long; anthers long; caryopsis 5.2-6.7 mm × 1.4-2 mm, red-brown.

• O. schlechteri. Perennial, tufted, stoloniferous; culm erect, 25-85 cm long; sheath tight; ligule collar-shaped, 1 mm long; nodes hairy; blade linear, 10-30 cm × 0.6-1.2 cm, with white hairs; panicle 4-6.5 cm long; spikelet 1.7-2.1 mm × 0.9-1.3 mm; sterile lemma 0.1-0.5 mm long; fertile lemma up to 2.1 mm long, awnless; caryopsis 1.1-1.3 mm × 0.7-0.9 mm, dark brown.

Growth and development

Little is known about growth and development. Growth is slow at the seedling stage. Oryza species form a group of C₃-cycle plants. Flowering occurs near the end of the prevailing rainy season. Grains are usually deciduous and often have a strong dormancy.

Other botanical information

Oryza is generally considered to belong to the tribe Oryzeae of the subfamily Bambusoideae and sometimes considered as a separate subfamily, the Oryzoideae. Related genera of Oryza in South-East Asia are Hygroryza Nees, Leersia Sw., Porteresia Tateoka, Potamophila R. Br. and Zizania L. Opinions differ about the number of species in the genus Oryza; it ranges from 18-22. Several species complexes exist, in which the taxa are difficult to distinguish from each other: e.g. O. meyeriana and O. granulata, which some consider to be one species O. meyeriana; O. officinalis and O. minuta, which some consider to be one species O. minuta; O. sativa and O. nivara, which some consider to be one species O. sativa.

Ecology

The wild rice species cover a wide range of habitats, ranging from open and often flooded areas, to partially or heavily shaded mesophytic niches, up to 1500 m altitude in the tropics. Tropical populations are largely perennial, subtropical taxa tend to be annual. O. nivara and O. rufipogon thrive under full sun, while all others are found under partial or full shade. Soil types vary from heavy clay to forest soils high in organic matter. Because seedlings usually grow slowly, populations are only found under stable conditions, away from fast-flowing streams and cliffs.

Agronomy

Deliberate cultivation only takes place for research purposes. Field-collected seed needs to be slowly dried and stored cold and dry. It should be sown at the beginning of the rainy season. Prior to seeding, strong grain dormancy should be broken by dry heat treatment (50 °C, 5-10 days), hulling, surface disinfection, and for unusually strong dormancy, the pericarp should be scratched near the embryo with a sterile needle. Treated seed is best germinated in Petri dishes and the sprouted seed transferred to a tray of fine soil. Healthy seedlings beyond the 3-leaf stage are transplanted into large clay pots, with several plants per pot. Seedlings and young plants need partial shading, careful watering, and light fertilization.

To multiply germplasm, plants are best kept in pots in a screenhouse for isolation and protection. Vigorously growing plants should be staked and tied, exserting panicles must be bagged with a porous bag or net to collect shattering seed. The identity of individual plants has to be checked, to ensure the nomenclature is correct. Herbarium specimens should be taken after first planting. Some species can be maintained by ratooning and repeatedly harvested for seed. Rhizomes or seed should not be allowed to escape into drainage canals or fields and become noxious weeds.

Genetic resources

A few decades ago the wild rice species were widespread and readily found in their native habitats. Development projects, deforestation and habitat disturbance have rapidly reduced population number and size. Neglect in maintaining drainage and irrigation canals has led to O. nivara and O. rufipogon being rapidly ousted by tall grasses and aquatic weeds. The future existence of nearly all wild taxa is threatened. Ex situ conservation in genebanks is both insufficient and inefficient: the wild populations are heterozygous and heterogeneous, requiring several plants to represent each, and seed production is meagre. Staff of the International Rice Research Institute (IRRI) have actively collected and assembled approximately 1400 samples, but further exploration and collection is needed in many inaccessible areas. In situ conservation with collaboration from local communities offers an alternative and more effective conservation approach, though its implementation is even more challenging. Field botanists should promote and expand in situ activities.

Breeding

Most wild rice species play an important role in breeding programmes to improve the cultivated rices O. sativa and O. glaberrima. Multidisciplinary evaluation at IRRI has revealed the enormous potential of wild species as sources of resistance to or tolerance of biotic and abiotic stresses. O. nivara has furnished the sole resistance to grassy stunt virus; O. officinalis is resistant to yellow stem borers, tungro virus and several planthoppers; O. minuta is resistant to blast and bacterial blight; O. rufipogon has the ability to elongate internodes (important for deep-water areas) and salinity tolerance. A weedy sterile plant found on Hainan island of China has provided the cytoplasmic male-sterility for 18 million ha of hybrid rices in China.

Prospects

With the advent of biotechnological innovations, the wild rices will quickly grow in economic potential for further enhancing rice production.

Literature

• Chang, T.T., 1976. Manual on genetic conservation of rice germplasm for evaluation and utilization. International Rice Research Institute (IRRI), Los Baños, the Philippines. 77 pp.
• Chang, T.T., 1985. Crop history and genetic conservation: rice - a case study. Iowa State Journal of Research 59: 425-455.
• Chang, T.T., 1988. Taxonomic key for identifying the 22 species in the genus Oryza. International Rice Research Newsletter 13(5): 4-5.
• Chang, T.T. & Vaughan, D.A., 1991. Conservation and potentials of rice genetic resources. In: Bajaj, Y.P.S. (Editor): Rice. Biotechnology in agriculture & forestry 14. Springer-Verlag, Berlin, Germany. pp. 531-552.
• Duistermaat, H., 1987. A revision of Oryza (Gramineae) in Malaysia and Australia. Blumea 32: 157-193.
• IRRI, 1991. Rice germplasm: collecting, preservation and use. International Rice Research Institute (IRRI), Los Baños, the Philippines. 173 pp.
• Tateoka, T., 1963. Taxonomic studies of Oryza. III. Key to the species and their enumeration. Botanical Magazine Tokyo 76: 165-173.
• Vaughan, D.A., 1989. The genus Oryza L. Current status of taxonomy. IRRI Research Paper Series 138. International Rice Research Institute (IRRI), Manila, the Philippines. 21 pp.
• Vaughan, D.A., 1994. The wild species of rice: a genetic resources handbook. International Rice Research Institute (IRRI), Los Baños, the Philippines. 137 pp.
• Vaughan, D.A. & Chang, T.T., 1992. In-situ conservation of rice genetic resources. Economic Botany 46: 368-383.

Authors

• T.T. Chang & Z. Harahap