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Rice

Cultural practices for characterization of wild rice

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).

Wild rice is best characterized during the seed regeneration process. So the following cultural practices are the same as the regeneration guidelines of wild rice.

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 usualy found in wet or seasonally wet habitats.   
  • Grow the plants in 30 cm wide-mouthed pots without holes, so they can be placed in different levels of shade in the screen house.

Planting season

  • Most of them are strongly photoperiod-sensitive so that the best time to grow them is during a season with short daylength 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 material for planting depends upon the available space in the screen house facility as space is usualy a limiting factor.  

  • When stocks are insufficient.
  • When viability reachs 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 or 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 labour 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 heterogeneos populations with low seed-set samples.
  • Otherwise, 3-4 pots are enough to produce seeds for storage.
  • Pots should be laid out at least 100 cm apart to provide sufficient ventilation between plants and enough space for plant management, but preventing from constant humid conditions that are conducive to disease development.
  • When pure lines are to be developed, only one plant per pot should be maintained and spaced widely, preferably alternating species of diferent 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 screen house.
  • For the highly photo-sensitive species like O.schlechteri, continued 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 three 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 one 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 provide 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 (15oC and 15% RH) for about 2-4 weeks.
  • Seeds should be authenticated and cross-referenced against the seedfile before carefully hand threshing and cleaning.
  • A 20 grain sample should be taken for seed viability testing.

Disposal of contaminated material

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

  • Carry out the seed multiplication of all wild rices inside the screen house 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 m 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 screen house with fine-mesh screens to further control dissemination of seeds through water.
  • Waste material 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 material (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 material, the disposal area should be treated with a non-selective herbicide (e.g. glyphosate).
  • Spray with herbicides to kill persistent species.
  • Screen house 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 screen houses should be regulated depending on the nature/importance of the visit.


Recording information

Consult the general rice characterization page for information about descriptors, or recording of information during characterization.

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. Springer Verlag, Berlin.

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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Cultural practices for characterization of cultivated rice

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).

Planting and cultural practices

Environment

Characterization trial of rice (photo: IRRI)

  • For large diverse collections encompassing varieties from different ecosystems, use irrigated lowland with good drainage (this provides a single common environment suitable for growing and comparing almost all varieties, including upland, lowland and deep water varieties, regardless of their normal ecosystem and adaptation).
  • For collections targeted to particular ecosystems, use the corresponding ecosystem (matching the ecosystem to the target provides more realistic characterization of varieties adapted to that ecosystem).

Note: In rice agriculture, the terms ‘upland’ and ‘lowland’ conventionally refer to the type of cultivation, not to the elevation of the land. Thus it is possible (and common) to have ‘upland’ rice in the lowlands and ‘lowland’ rice in the uplands.

‘Upland’ = on sloping land never inundated in water.

‘Lowland’ = on level ground periodically inundated, by rainfall or by irrigation water, to control weeds.

Soil type

  • Silt clay to clay loam (best for lowland rice cultivation).

Rainfall

  • Medium-high, or irrigate (rice does not grow well under drought; it needs either abundant rainfall or effective irrigation).

Season

  • As appropriate to rice cultivation in the region.
  • In tropical areas with two cropping seasons per year, select one season per year for characterization: usually the season that starts while days are growing longer.
  • Long-duration varieties will extend into the second cropping season (using one fixed season each year improves consistency between trials.
  • Some rice varieties are short-day photoperiod sensitive.
  • In tropical latitudes higher than about 10°, the sensitivity to photoperiod (a key trait) can be tentatively characterized without multiple treatments by planting as the days are growing longer (e.g. in April-May in the northern hemisphere, October-November in the southern hemisphere); photoperiod sensitive accessions then remain vegetative for a prolonged period until the days shorten again. However, this does not distinguish between photoperiod-sensitive and long-duration photoperiod-insensitive varieties).

Plot size

  • 5 m2 - 3 rows 5 m long (minimum plot size providing one row for sampling and one border row on each side).

Sampling area/border area

  • Sampling area - one central row.
  • Border area - one row on the edge of each plot, i.e. two border rows between successive sampled rows (minimum area good enough to record required traits at minimum maintenance cost).

Plant density

  • Single seedling per hill, 30 x 30 cm between hills (use wider spacing than common agricultural practice for improved recording of tillering ability).

Replications

  • Normally unreplicated entries, control varieties are replicated every 150 entries (replication of only control varieties is sufficient for normal assessment of highly heritable morpho-agronomic traits; more economical and thus allowing the screening of more accessions).
  • For special purpose characterization for more rigorous statistical analysis, full replication is necessary.

Standard check cultivars

  • For large diverse collections spanning all types, use up to six control varieties from the main taxonomic variety groups (glaberrima, indica, japonica, aus) and morpho-agronomic groups (glutinous, semi-dwarf).
  • For smaller collections targeted at a particular ecosystem or environment, use a smaller number of check cultivars as appropriate for the target ecosystem and environment.

Frequency of standard checks

  • Plant the full set of selected check varieties every 150 entries (this is the best practices considering the number of entries being handled and randomly scattered across the entire size of the field).

Time of day for data collection

  • Field data are best collected in the morning (best time for consistent characterization of traits such as flowering that vary through and are most apparent in the morning. Best time also for the effectiveness of the observer).
  • Post-harvest data can be taken any time, but for efficient use of time, good practice is to alternate field work in the morning with post-harvest characterization indoors in the afternoon.

Consult the general rice characterization page for information about descriptors, or recording of information during characterization.

References and further reading

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.

Rao NK, Jackson MT. 1996a. Seed longevity of rice cultivars and strategies for their conservation in genebanks. Annals of Botany 77:251–260.

Rao NK, Jackson MT. 1996b. Seed production environment and storage longevity of japonica rices (Oryza sativa L.). Seed Science Research 6:17–21.

Rao NK, Jackson MT. 1996c. Effect of sowing date and harvest time on longevity of rice seeds. Seed Science Research 7:13–20.

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).

Reaño R, Pham JL. 1998. Does cross-pollination between accessions occur during seed regeneration at the International Rice Genebank? International Rice Research Notes 23(3):5–6.

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.

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

Cultural practices for regeneration of cultivated rice

View regeneration guidelines in full (in PDF)
by clicking on the picture above (0.4MB)

Also available in the following languages:
Arabic - French - Portuguese - Russian - Spanish

This information was extracted from: Reano R, Sackville Hamilton R, Romero G. 2008. Regeneration guidelines: rice. In: Dulloo ME, Thormann I, Jorge MA, Hanson J. (editors). Crop specific regeneration guidelines [CD-ROM]. CGIAR System-wide Genetic Resource Programme, Rome, Italy. 11 pp.

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

Cultural practices

Climatic conditions

Rice has a tropical to warm-temperate distribution and is widely grown in every continent except Antarctica.

  • It can be grown from the equator to about 53°N in China and 30–40°S over 3.5 to 6 months.
  • Some relatively cold-tolerant varieties can grow at altitudes up to 3000 m.
  • O. glaberrima , which is normally grown under upland or dry conditions and directly sown in the field, can normally be successfully regenerated under lowland conditions similar to those of O. sativa.

Planting season

Regenerating rice accessions at IRRI, Philippines. Note diversity in maturity and plant architecture (photo: Renato Reaño/IRRI)

  • Regenerate plants in the dry season.
  • The dry conditions, short day-length and low (25–26°C) temperatures during grain filling allow for optimal seed production of tropical indicas and temperate japonicas, and pest and disease incidence is relatively low as well.
  • The crop is ready for harvest during the period of lowest ambient relative humidity and rainfall.
  • For specific groups, such as photoperiod sensitive materials, adjust planting so that plants are at maximum vegetative growth when short day-length occurs.
  • Recalcitrant temperate japonicas, upland varieties and accessions with critically low seed quantities or poor viability, which are too risky for field planting, should be regenerated under mesh screens, in growth chambers maintained at cooler temperatures or at a cooler location.

Preparation for regeneration

When to regenerate

  • When stocks are below 60g in the active collection and below 120g in the base collection.
  • When germination rates during storage fall from 85–100% to 72–85% (85% of initial rates).

Pre-treatments

  • Adjust seeds to ambient temperature, then place in ovens set at 50ºC for 48–72 hours to break dormancy, followed by equilibration at ambient temperature for 24 hours before seeding.
  • For old seeds, soak in 1000ppm gibberellic acid for 20 hours or dehull to break dormancy.

Preparing furrows in a raised seedbed using an improvised wooden implement (photo: Roel C. Rabara/PhilRice)

Field selection and preparation

  • Loamy-clay soil is ideal and good irrigation and drainage facilities are necessary to provide appropriate water management for diverse germplasm with different moisture adaptations.
  • Prepare land by ploughing the field once, harrowing two or three times, and levelling.
  • Prepare a modified wet bed or a dry bed for sowing.
  • Form beds of 5–10m long and 0.8m wide, raised by about 15cm for the dry bed or 10cm for the modified wet bed, and make furrows 10cm apart (see photo).
  • Construct the dry bed in a dry area after thorough land preparation. Form the modified wet bed from paddied soil without standing water 2–3 days after cultivation.

Method of regeneration

Planting layout, density and distance (see photo below)

  • Depending on the percentage germination and the required amount of seeds, 20–30g will be enough for a standard plot.
  • Plant at least 100 seedlings per plot to produce between 2000 and 35 000 healthy and highly viable seeds (equivalent to 50–700g).
  • Planting in larger plots is recommended for frequently requested accessions.
  • Number field plots from left to right and right to left in alternating rows (see figure).
  • Each plot should have eight 5-m long rows spaced 25cm apart.
  • Transplant single seedlings 25cm apart, filling 21 hills per row.
  • Leave two rows vacant between plots.

Rice accessions growing in the field (photo: Roel C. Rabara/PhilRice)

Schema for numbering field plots. (photo: Renato Reaño/IRRI)

 

Sowing method

  • Irrigated rice is generally transplanted while O. glaberrima and upland rice are direct seeded, but for seed regeneration for genebanks, transplant all accessions to facilitate field management.
  • Sow seeds in seedbeds evenly along the rows and cover with garden soil or top-soil (see photo), then transplant seedlings by hand into the field plots in straight lines 18–30 days after sowing (see photo).

After sowing, seeds are covered with soil (photo: Roel C. Rabara/PhilRice)

Bundled seedlings are distributed in
the field following the planting plan and
manually transplanted (photo: Roel C. Rabara/PhilRice)

 

  • Compared with direct seeding, transplanting gives better seedling establishment, superior control over spacing and allows easier identification of volunteer plants.

Seedbed management

  • Apply 10kg N per hectare.
  • Apply granular insecticide to control ants, crickets and nematodes.
  • Intermittently irrigate dry beds with an overhead sprinkler and modified wet beds by flooding, taking care not to submerge the bed so as to avoid mixing seeds between rows.
  • Monitor and control any seedling pests.

Isolation (method)

The following procedures are recommended for isolating plants:

  • Establish regeneration plots 2 weeks earlier than surrounding crops.
  • Leave a space equivalent to 2 rows of rice between adjacent plots as fallow.
  • Harvest only the inner rows, leaving one border row on each side.
  • Arrange plots so that adjacent varieties have projected flowering dates separated by at least 10 days.
  • Regenerate post-quarantine, original incoming samples in one of the following:
    • In an isolated field at least 150–200m from other rice fields.
    • In a field surrounded by a physical barrier to movement of disease and pest organisms, such as shrubs or trees to act as a windbreak.
    • In a screenhouse.

Label of the accession attached to the bunch of seedlings (photo: Roel C. Rabara/PhilRice)

Labelling

  • Generate a seedlist containing plot numbers and accession numbers.
  • Mark envelopes or seed packets for planting with the corresponding plot number.
  • Mark the entries on the seedbed with 20cm wooden labels (or equivalent) bearing plot numbers printed in indelible ink.
  • Attach the relevant tags to the bunches of seedlings for planting (see photo).
  • After planting out the seedlings attach the tags to bamboo stakes (or equivalent) to serve as field plot labels.

Crop management

Weed management

  • Effective weed management in transplanted rice begins with a good irrigation system and good land preparation.
  • Apply pre-emergent herbicides immediately after transplanting or before the weed seeds start to germinate, complemented with good irrigation within 5 days after transplanting.
  • Hand weed at 21 to 30 days after transplanting before applying fertilizer. Spot-weed when necessary.

Irrigation and flooding

  • Transplanted rice requires irrigation or standing water (2–3cm) in the first 5 days for efficient weed control.
  • An alternating irrigation and drainage system may be needed, especially if there are entries of upland types and O. glaberrima.
  • Ensure sufficient water is available at flowering to enhance seed set and avoid any reduction in fertility.

Fertilization

  • Adequate fertilization is necessary to grow vigorous rice plants and produce a good yield.
  • Determine the rate and type of fertilizer to use either from soil analysis or by using the Spad meter.
  • At IRRI Experimental Station, the recommended fertilizer rate for dry season cropping is 90-30-30kg N-P-K per hectare. Split application of nitrogen is made, with basal at planting, first top dressing after first weeding at about 21–30 days after transplanting or at maximum tillering, and second top dressing at panicle initiation by spot application. All the phosphorus and potassium are applied at planting.
  • Nutrient supplementation may be applied by root dipping seedlings in 4% zinc oxide prior to transplanting.

Common pests and diseases

Contact plant health experts to identify pests and diseases and appropriate control measures. Some of the major pest and diseases of rice are as follows:

Viruses

  • Tungro (rice tungro bacilliform virus (RTBV) and spherical virus (RTSV))
  • Grassy stunt (rice grassy stunt virus) (RGSV)
  • Ragged stunt (rice ragged stunt virus) (RRSV)
  • Rice streak virus (RSV)

Fungi

  • Rice blast, Pyricularia grisea (Cooke) Sacc.
  • Sheath blight, Rhizoctonia solani (Kuhn)
  • Brown spot, Bipolaris oryzae (Breda de Haan) Shoemaker
  • Bakanae disease, Gibberella fugikuroi
  • Seedborne: Stackburn disease, Alternaria padwickii; Curvularia spp.

Bacteria

  • Bacterial leaf blight, Xanthomonas oryzae pv. Oryzae (Ishiyama) Swing et al.
  • Bacterial leaf streak, Xanthomonas oryzae pv. Oryzicola (Fang et al.) Swing et al.
  • Bacterial grain rot, Pseudomonas glumae

Nematodes

  • Ufra or stem nematode, Ditylenchus angustus Butler
  • White tip, Aphelenchoides besseyi Christie
  • Root knot, Meloidogyne graminicola Golden & Birchfield
  • Rice root nematode (Hirschmanniella imauri , Hirschmanniella oryzae)

Insects

  • Green leafhopper (Nephotettix malayanus; N. virescens)
  • Planthopper: brown planthopper, Nilaparvata lugens (Stal); whitebacked lanthopper, Sogatella furcifera (Horvath)
  • Rice bug, Leptocorisa oratorius (Fabricius); L. chinensis (Dallas); L. acuta (Thunberg)
  • Stem borer: yellow stem borer, Scirpophaga incertulas (Walker); white stem borer, S. innotata (Walker)
  • Rice black bug, Scotinophara coarctata (F.)
  • Golden apple snail, Pomacea canaliculata Lamarck

Pest and disease control

Preventive

  • The cheapest and most practical way for preventing attacks of insect pests, rodents and diseases is field sanitation.
  • An active barrier system also helps prevent rodent attacks.
  • Apply preventive insecticides to assure early protection.
  • A systemic insecticide such as Carbofuran 3G can prevent early attacks from leaf cutting insects and maggots.
  • Snails are present in standing water.
  • After the final land preparation, construct small canals to facilitate drainage.
  • During the first 2 weeks of crop establishment, drain and flash-flood the field several times to flush out golden snails.

Non-preventive

  • Apply other pesticides during the vegetative stage against hoppers and borers.
  • Apply knock-down insecticide at flowering and reproductive stage against stem borer and rice bugs.
  • For fields with standing water, control golden snail by picking up snails and applying molluscicide.

Special care

  • Remove rogue plants throughout the growing period.
  • When regenerating a diverse or mixed accession, consult the seed file, original seed sample and remnant seed samples in order to avoid excessive roguing and associated genetic drift.
  • Always note when mixed samples are planted and take care not to weed out types which are contained within the accession.
  • After rounds of harvesting in a certain area, carry out flash flooding to moisten the soil for late maturing entries.
  • Put net bags over panicles of accessions that are prone to rachis shattering to catch the seeds.

Harvesting

  • Harvest about 28 to 35 days after flowering or at 80% maturity of the spikelets.
  • Cut panicles and place them in clean cloth bags with tags indicating plot number and date.
  • Harvest O. glaberrima and other shattering germplasm earlier, with each panicle harvested at the stage just before the time of shattering.
  • Some other accessions may also need to be harvested by individual panicle, due to variation in maturity within the accession.
  • This will avoid pre-harvest sprouting for nondormant entries as well as deterioration to early maturing in the population (i.e. genetic drift).

Post-harvest management

Seed cleaning

  • Hand thresh or process harvested panicles with a self-cleaning thresher (Vogel type).
  • Clean grains initially by blowing off inert matter, weed seed and half-filled grains and then transfer to net bags along with two shipping tags marked with the plot number and date of harvest.
  • Clean and select seed manually at 40–50% RH and 22°C to eliminate poor quality seeds and off-types.

Seed drying

  • Place seeds in the drying facility at 15°C and 15% RH for about 1 week to bring them to 8–10% moisture content. Alternatively, air-dry them for 3–4 weeks in a well-ventilated room, preferably with electric fans and dehumidifiers under 15–25°C to bring them to 11–13% moisture content.
  • Transfer dry seeds to paper bags for another round of seed blowing.
  • Verify harvest against the seed file and discard if unmatched.
  • Place seeds in the drying facility for another week to achieve 5–8% moisture content while awaiting viability and seed-health test results. Alternatively, incubate seeds over 4–8 weeks under 20–25°C in a glass jar with an equal amount of activated silica gel or appropriate desiccant that is changed two or three times during the drying period upon colour change of indicator.

Seed testing

  • Perform a viability test on 100 seeds (pre-incubated at 50°C for 5 days and room temperature for 2 to 3 days to break dormancy) with two replicates on moist paper towels under ambient temperature and 12/12 hour light/dark condition. Score viability after 7 and 14 days following ISTA rules.
  • Test seed health following standard procedures and discard infected seeds.
  • Determine moisture content by oven-method (130°C for 2 hours) on a 5g sample following ISTA rules.

Seed packaging

  • Select seeds that are at 5–8% moisture content, clean, free from pests and with >85% viability and divide into base, active and/or duplication collections for conservation in aluminium foil or paper envelopes.
  • Place seeds in paper envelopes in jars containing 30% silica gel.
  • At IRRI, each accession is stored in: 1) Base collection with up to two 60-g samples in an aluminium can; 2) Active collection with two to five 10-g samples and one 500-g sample in aluminium foil; and 3) Duplicate set with two 15-g samples in aluminium foil.
  • Store the base collection in long-term conditions at -20 to -18°C, and the active collection in a medium-term room at +5 to +25°C.

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

References and further reading

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

Rao NK, Jackson MT. 1996a. Seed longevity of rice cultivars and strategies for their conservation in genebanks. Annals of Botany 77:251–260.

Rao NK, Jackson MT. 1996b. Seed production environment and storage longevity of japonica rices (Oryza sativa L.). Seed Science Research 6:17–21.

Rao NK, Jackson MT. 1996c. Effect of sowing date and harvest time on longevity of rice seeds. Seed Science Research 7:13–20.

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).

Reaño R, Pham JL. 1998. Does cross-pollination between accessions occur during seed regeneration at the International Rice Genebank. International Rice Research Notes 23(3):5–6.

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.

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

Acknowledgement

These guidelines have been peer reviewed by Teresita Borromeo and Sancho G Bon, University of the Philippines Los Baños, Philippines; Tiur Sudiati Silitonga, Indonesian Centre for Agricultural Biotechnology and Genetic Resources Research and Development (ICABIOGRRAD), Indonesia; and Kim Taesan, RDA Genebank, Korea.

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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.

Regeneration guidelines for wild rice and related genera

Contributors to this page: T.T. Chang Genetic Resources Centre-IRRI, Los Baños, Philippines (Ruaraidh 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).

Provides guidelines and recommendations about the best practices for the daily management of genebanks, describing the most important procedures to regenerate wild rice and related genera. Best practices are shown in a pale blue color with bullets. Justification for each best practice is given within brackets (…).


Storage specifications

Choice of environment and planting season


Climatic conditions

  • Most accessions of wild rices require different cultural management practices for seed increase compared to those of the cultivated rices.
  • Several species such as O. meyeriana, O. granulata, O. ridleyi, and O. longiglumis grow better under partial shade, while others grow well under full sunlight.
  • Grown the plants in 30 cm wide-mouthed pots without holes, so they can be placed in different levels of shade in the screen house.
  • Wild species are also known to have stronger dormancy than the cultivated species.

Planting season

  • Most of them are strongly photoperiod-sensitive so that the best time to grow them is during a season with short daylength to induce panicle initiation.

Preparation for regeneration

When regenerate?

  • When stocks are below??

Pre-treatments

Wild species are also known to have stronger dormancy than the cultivated species.
  • Apply .... to break dormancy??

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 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.
  • 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.
  • The pots should be laid-out at least 100 cm apart to provide sufficient ventilation between plants and enough space for plant management.
  • 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.

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 three weeks, 30 days after transplant.

Irrigation

  • Plants should be watered daily.

Pest and disease control

  • Plant health should be monitored regularly.
  • Appropriate control measures should be applied to specific pest and diseases once symptoms appear.
  • Maintaining the cleanliness of plants also helps preventing the spread of diseases.

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.
  • After harvesting, the panicles should be dried and kept inside the drying room for two weeks, before carefully hand-threshing and cleaning the seeds.

Post harvest management

Disposal of contaminated material

 


Storage management

Documentation of information during regeneration

System for tracking material/inventory system during regeneration

 
  • Use databases of stock and location (databases are needed to keep track of information).
  • Use pegs, tags or barcodes for labelling:
    • Use impermeable ink and write clearly.
    • Plots must be well labelled to avoid errors.
    • Barcodes help avoid errors in recording.

Recording information during regeneration

The following information should be recorded for each step:

  • Site name and map/GPS reference.
  • Name of collaborator.
  • Regeneration site name (a code to identify the site location).
  • Plot reference (the plot number at the field site).
  • Accession number; population identification.
  • Name of staff (name of staff recording the data).
  • Method of planting, date and spacing.
  • Screen house layout used.
  • Screen house management details (watering, fertilizer, weeding, pest and disease control, stresses recorded, others).
  • Environmental conditions (altitude, precipitation, temperature, soil type and others).
  • Number of plants established.
  • Days from planting to flowering (note: this will only be important if seed collection is anticipated).
  • Harvest date and method.
  • Number of plants harvested.
  • Comparisons with reference materials (record any identification numbers or references of any samples taken from the plots).
  • Any evaluation undertaken during the growing period or at harvest.
  • Post harvest (describe any relevant procedures).
  • Others.

References and further reading


 

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