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Cultural practices for regeneration of wild rice and related genera

Contributors to this page: T.T. Chang Genetic Resources Centre-IRRI, Los Baños, Philippines (Ruaraidh Sackville Hamilton, Ken McNally, Flora de Guzman, Renato Reaño, Soccie Almazan, Adelaida Alcantara, Elizabeth Naredo); WARDA, Cotonou, Benin (Ines Sánchez); UPLB-University of the Philippines at Los Baños (Teresita Borromeo).

Before reading the regeneration details for this crop, read the general introduction that gives general guidelines to follow by clicking here.


General guidelines

Understanding the biology of wild rice plants and knowledge of the natural growing habitat of the different species is very important for the initial seed multiplication of a specie.

  • Wild species have prolonged extended flowering period, however, the initial flush of flowering usually produces the most seeds, particularly for annual or weakly perennial species.
  • Panicle bagging is necessary to minimize out crossing, to prevent seed loss due to shattering, and to prevent mixtures at harvesting.
  • Seeds are usually produced in small quantities because some species have high seed sterility.
  • Some outcrossing species can naturally hybridized with the cultivated rice, thus growing them in a separate location from the cultigen preferably a screened nursery area or a screenhouse facility is required.
  • Plants should be grown in pots.
  • Systematic plant characterization should be done using morpho-agronomic traits along with the initial seed multiplication.

Choice of environment and planting season

Climatic conditions

  • Most accessions of wild rice require different cultural management practices for seed increase compared to those of the cultivated rices.
  • During plant growth it is necessary to simulate the habitat/growing environment of the original collection sites of each of the species to promote flowering.
  • Cultural practices should be integrated with intensive monitoring of pests and diseases.
  • Several species such as O. meyeriana, O. granulata, O. ridleyi, and O. longiglumis grow better under partial shade, while others like some of the O. sativa complex grow well under full sunlight. These are usually found in wet or seasonally wet habitats.   
  • Grow the plants in 30cm wide-mouthed pots without holes, so they can be placed in different levels of shade in the screenhouse.

Planting season  

  • Most of them are strongly photoperiod-sensitive so that the best time to grow them is during a season with short day length to induce panicle initiation.
  • Planting of wild rice should be planned so that plants reach the reproductive stage when the shortest day length occur. In the Philippines they should be planted during the wet season (June) so that they have the reproductive stage during the shortest days that occur in December. 

Preparation for regeneration

When to regenerate

The frequency of regeneration is determined by the quantity of seeds stocks left at the genebank.

The selection of materials for planting depends upon the available space in the screenhouse facility as space is usually a limiting factor.  

  • When stocks are insufficient.
  • When viability reaches low or zero values.
  • When seed samples are infected.
  • When morphological characterization is scheduled.
  • When there are small seed quantities from newly received samples.
  • When there are highly heterogenous samples.

Propagation method

  • Wild taxa are readily propagated by seeds.
  • Some species like O. schlechteri are maintaned asexually through its vegetative stolons.
  • O. longistaminata is maintained asexually with its rhizomes.
  • Other perennial species can also be propagated by separating tillers of its vegetative crown. 

Breeding system

  • Rice is self-pollinated but some wild species have some degree of out crossing.

Isolation

  • Artificial barriers like net bags, glassine bags should be used to control inter-accession pollination.
  • Net fencing using net curtains should be constructed to separate species like O. longistaminata.
  • Pots should be planted with alternating species of different complexes.

Pre-treatments

Wild species are known to have stronger dormancy than the cultivated species. They may require one or a combination of dormancy breaking treatments including heat treatment, dehulling, exposure to alternating temperatures, and in some cases chemical treatments.

Heat treatment

  • In most species, heat treatment at 50°C for 10-14 days, followed by acclimatization at room temperature for 5-7 days is done before hull removal to promote germination of newly harvested seeds.
  • If seeds are withdrawn from storage facility, allow 2-3 days for the seeds to adjust to room temperature before applying heat treatment.
  • For species belonging to O. sativa complex, exposure to alternating temperatures of 45ºC and 30ºC (45/30) is generally effective in breaking dormancy. It is recommended, however, that the seeds be transferred to 30ºC after radicle emergence to achieve maximum seedling growth.

Dehulling

  • Seed hull removal is recommended for most species to effectively break seed dormancy, but it is labor intensive and demands great care as not to damage the seed embryo.
  • Treat dehulled seeds with a fungicidal suspension and wash thoroughly.
  • Germinate on moist filter paper in petri dishes and place inside a germinator with 30°C and 100% RH.

Chemical treatment

  • For some species, chemical treatment and/or dry heat method are more applicable and efficient when handling a large number of samples.

Method of regeneration

Sowing method

  • Plant the germinated seeds 1-2 cm apart, in a seed box containing moist, fine, clean (preferably sterilized) soil mixed well with appropriate amount of ammonium sulfate.
  • Apply a granular insecticide (e.g. Furadan) 3-4 days after planting to protect the seedlings from ants and other insects.
  • Water the seedlings carefully with a fine spray, and grown them under partial shade until a week before transplanting.

Transplanting

  • Transplant the seedlings 30 days after sowing to water- tight pots with good quality soil mixed with about 5 g of complete fertilizer.
  • Maintain the water level to at least 1-2 cm depth.
  • A granular insecticide (e.g. Carbofuran) should be applied 7 and 14 days after transplant to protect the plants against hoppers and defoliators.

Planting layout, density and distance 

  • Use 5-10 pots for highly heterogeneous populations with low seed-set samples.
  • Otherwise, 3-4 pots are enough to produce seeds for storage.
  • Pots should be laid-out at least 100cm apart to provide sufficient ventilation between plants and enough space for plant management but preventing from constant humid conditions that are conducive of disease development.
  • When pure lines are to be developed, only 1 plant per pot should be maintained and spaced widely, preferably alternating species of different complexes.
  • If a bulk population is required, 2-3 seedlings per pot should be transplanted and all plants maintained.  

Planting conditions 

  • For species of the O. meyeriana complex, the seedlings should be transplanted into pots with light soil and good internal drainage to prevent water logging as they thrive best in mesophytic conditions.
  • For the highly stoloniferous species, such as O. schlechteri and some related genera like Luziola, Leersia, and Hygroryza, a modified flat bed should be constructed and used for growing and maintaining a single accession.
  • All species of the genus Oryza grow well under full sunlight except members of the O. meyeriana complex and O. ridleyi complexes which are best maintained in partial shade.
  • Accessions difficult to germinate should be cultured on agar, and seedlings raised in culture solution in the Phytoron facility, where growth environment can be modified, before transfer and reared in the screenhouse.
  • For the highly photo-sensitive species like O.schlechteri, continue modifications of conditions for flower induction may be needed. 

Different varieties of rice being grown inside an IRRI green house (photo: IRRI)

Crop management

Fertilization

  • Top dressing is recommended at 30 and 45 days after transplant with 5 g ammonium sulfate per pot.
  • For O. meyeriana complex, 2 g of ammonium sulfate should be applied weekly during 3 weeks, 30 days after transplant.

Irrigation

  • Plants should be watered daily, maintaining at least 1-2 cm depth.

Pest and disease control

  • Plant health should be monitored closely and regularly, with seed health unit inspectors as well as representatives from governmental health offices.
  • Appropriate and intensive control measures should be applied to specific pest and diseases once symptoms appear.
  • Spray liquid insecticides (emulsifiable concentrate and/or wettable powder) when need arises.
  • Spraying soap detergent can help to control some small sucking insect pests.
  • Maintaining the cleanliness of plants also helps preventing the spread of diseases.
  • Infected/diseased plants should be rouged and eliminated.

 Thinning

  • When purelines are to be developed, only 1 plant per pot should be maintained and spaced widely, preferably alternating species of different complexes.
  • If a bulk population of seeds is required, 2-3 seedlings per pot should be transplanted and all the plants should be maintained.

Harvesting

Panicle bagging

  • At the late vegetative stage, (about 60 days after transplant) the tillers should be tied loosely with for example an abaca twine to a bamboo stake (5 cm x 2 m) to prevent plants from encroaching from one pot to another, at the late reproductive stage, to facilitate panicle bagging.
  • Panicle bagging is necessary for handling wild rices to minimize outcrossing, to prevent seed loss due to shattering, and to prevent mixtures at harvesting.
  • Panicles should be bagged a week after full panicle emergence using nylon net bags which provides ample ventilation to facilitate anther dehiscence and prevent mold formation on glumes.
  • For species with shorter panicles, glassine bags are a good substitute.
  • The net bag should be pinned to the bamboo pole.
  • Prior to bagging, labels should be prepared using shipping tags written with plot number and date of bagging with indelible ink.
  • The labels must be attached inside the net bags.

Rice being grown inside an IRRI screen house. Notice the bagged panicles (photo: IRRI)

Panicle harvesting

  • The panicles should be harvested 30 days after bagging or when most of the seeds have shattered.
  • If sufficient seeds are obtained, the plants should be discarded and disposed through burning.
  • However, for species with low seed set like O. rufipogon and O. longistaminata, the plants should be ratooned by cutting about 20-25 cm from the culms base, a little amount of ammonium sulfate should be applied and plants should be maintained until the next flowering to maximize seed production.

Post harvest management

Seed processing

  • After harvesting, the panicles should be dried slowly to 6% moisture content and kept inside a drying room (15°C and 15% RH) for about 2-4 weeks.
  • Seeds should be authenticated and crossed-referenced against the seedfile before carefully hand-threshing and cleaning.
  • A 20 grain sample should be taken for seed viability testing.

Disposal of contaminated materials

To ensure plants do not spread by seeds or rhizomes, specific measures should be followed:

  • Do the seed multiplication of all wild rices inside the screenhouse in pots.
  • Quarantine measures should be strictly followed to further minimize dissemination of seeds or rhizomes.
  • Designate a disposal area (a pit about 3-4 meters deep from the surface ground) for burying discarded and burnt samples to properly control spread of seeds or rhizomes.
  • Provide a modified incinerator or burning facility to accommodate burning activities especially during the rainy season.
  • Cover all drainage canals inside the screenhouse with fine-mesh screens to further control dissemination of seeds through water.
  • Waste materials from the canals should be regularly hauled, burned, and buried.
  • If sufficient seeds are obtained, old plants should be discarded, burned and buried into the pit.
  • Excess planting materials (seeds, seedlings, rattooned tillers) should be collected, burned and buried after seeding, transplanting and/or replanting.
  • Discarded soil used in growing should be treated with herbicide and buried in the designated area.
  • Before filling up all the discarded materials, the disposal area should be treated with a non-selective herbicide (e.g. glyphosate).
  • Spray with herbicides to kill persistent species.
  • Screenhouse staff should be advised to change their working clothes to minimize dispersal of seeds when they leave.
  • Hand threshing and seed cleaning should be done in a specified room in the Seed Processing Area of the genebank.
  • All dried leaves/straws, unfilled grains, mixtures and off-types must be collected, burned and buried.
  • The access to screenhouses should be regulated depending on the nature/importance of the visit.


For information about monitoring accession identity and documentation of information during regeneration, click here

References and further reading

Borromeo TH, Sanchez PL, Vaughan DA. 1994. Wild rices of the Philippines. Philippine Rice Research Institute, Maligaya, Nueva Ecija, Philippines.

Chang TT, Vaughan DA.1989. Conservation and potentials of rice genetic resources. In: Bajaj YFS, editor. Biotechnology in agriculture and forestry. Berlin: Springer Verlag.

Hanson J. 1985. Practical Manuals for Genebanks: Procedures for handling seeds in genebanks. IBPGR, Rome, Italy. HTML version available from: http://www2.bioversityinternational.org/publications/Web_version/188/. Date accessed: 10 June 2010.

Lu BR. 1999. Taxonomy of the genus Oryza (Poaceae): Historical perspective and current status. IRRN 24.3. IRRI, Los Baños, Laguna.

Manual of operations and procedures of the International Rice Genebank. 2000. Genetic Resources Center, IRRI. Available here.

Naredo MEB, Juliano AB, Lu BR, de Guzman FC, Jackson MT. 1998. Responses to seed dormancy breaking treatments in rice species (Oryza L). Seed Science and Technology, 26:675-689.

Rao NK, Hanson J, Dulloo ME, Ghosh K, Nowel D, Larinde M. 2006. Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy. Available in English (1.5 MB),  Spanish (1.4 MB) and French (1.9 MB).

Reed BM, Engelmann F, Dulloo ME, Engels JMM. 2004. Technical guidelines for the management of field and in vitro germplasm collections. Handbook for Genebanks No. 7. IPGRI, Rome, Italy. Available here.

Sackville-Hamilton NRS, Chorlton KH. 1997. Regeneration of accessions in seed collections: a decision guide. Handbook for Genebanks No. 5. IPGRI, Rome, Italy. Available here.

Tateoka T. 1962a. Taxonomic studies of Oryza I. O. latifolia complex. Bot. Mag. Tokyo 75: 418-427.

Tateoka T. 1962b. Taxonomic studies of Oryza II. Several species complexes. Bot. Mag. Tokyo. 75: 455-461

Tateoka T. 1963. Taxonomic studies of Oryza III. Key to the species and their enumeration. Bot. Mag. Tokyo. 76: 166-173.

van Soest LJM. 1990. Plant Genetic Resources: Safe for the future in genebanks. Impact of Science on Society 158: 107-120.

Vaughan DA. 1989. The genus Oryza L. Current status of taxonomy. IRRI Research Paper Series 138, Manila, Philippines.

Vaughan DA, Sitch LA. 1991. Gene flow from the jungle to farmers. Bioscience Vol. 41(1):22-28.

Vaughan DA. 1992. The wild relatives of rice: A genetic resources handbook. IRRI, Los Baños, Philippines.

Vaughan DA, Chang TT. 1992. In situ conservation of rice genetic resources. Economic Botany 46(4): 368-383.

Vaughan DA, Morishima H, Kadowaki K. 2003. Diversity in the Oryza genus. Current Opinion 6:139-146.

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