· Hybrid rice seed is produced when the egg is fertilized by pollen from the anthers of a rice plant from a different variety or line.
· Hybrid rice seed is the first filial (F1) generation of a cross of two rice varieties that are genetically different.
· A rice line that cannot produce viable pollen due to the interaction between cytoplasmic and nuclear genes is described as being cytoplasmic male sterile (CMS).
· It is used as a female parent for hybrid rice seed production.
· The male sterile line is commonly called a CMS line, the seed parent, the female parent, or the A line.
· Panicles may not exsert fully. Their basal portion remains inside the flag leaf sheath.
· Anthers are pale or white and shrivelled.
· The flowering period usually lasts for 7 days.
· A maintainer line is similar to a CMS line except that it has viable pollen grains and normal seed setting.
· The maintainer line is used as a pollinator for maintaining a CMS line.
· The maintainer is also called the B line.
· The B line cannot restore fertility to the F1 generation when it is crossed with a CMS line.
· Panicles exsert fully out of the flag leaves.
· Anthers are yellow, plump, and shed pollen.
· The B line flowers 2-3 days earlier than the CMS line.
· Flowering lasts for about 5 days.
· Any rice cultivar that restores fertility in the F1 when it is crossed to a CMS line is called a restorer.
· The restorer is also called the pollen parent, the male parent, or the R line.
· The R line is used as the pollinator for the CMS parent for hybrid seed production.
· Growth duration may or may not be similar to that of CMS lines.
· Panicles exsert fully out of the flag leaves.
· Anthers are yellow, plump, and shed pollen.
· Flowering lasts for about 5 days.
Synchronization of Flowering
Synchronization of flowering can be done in two ways:
1. We can adjust the seeding dates of the parents in the seedbed so they flower at the same time in the field. That is called differential seeding. Seeding time always depends on the growth duration of the parents, whether you are multiplying a CMS line or producing hybrid seed.
2. We can adjust the flowering date in the field by crop management practices later in the growing season. These are explained in the section on entitled Adjusting flowering date.
· In hybrid seed production, we normally seed the R line three times. The seeding dates are separated by 3-day intervals.
· The A line is always seeded just once.
· The seeding of the A line and the second seeding of the R line are separated by the number of days difference in their growth duration.
If the A line growth duration is shorter, the second R line seeding is done before the A line.
Example 1:
R line growth duration = 100 days A line growth duration = 90 days
The A line has a 10-day shorter growth duration; therefore the second seeding of the R line will be 10 days before the A line.
If the A line growth duration is longer, the second R line seeding is done after the A line.
Example 2:
R line growth duration = 90 days A line growth duration = 100 days
The A line has a 10-day longer growth duration; therefore the second seeding of the R line will be 10 days after the A line.
· If both parental lines have the same growth duration, the A line seeding and the second R line seeding would be done on the same day.
· We do the first seeding of the R line 6 days earlier than the second seeding. We do the third seeding of the R line 6 days later than the second seeding.
· We try to synchronize flowering of parental lines by differential seeding.
· Weather fluctuations during the growing season and crop management practices may cause the parental lines to flower on different dates.
· When flowering is not synchronized, hybrid seed yield will be reduced.
· Flowering date of parental lines cannot be accurately predicted until the crop is at maximum tillering stage.
Panicle initiation and flowering date
· Flowering date is predicted on the basis of panicle initiation.
· Panicle initiation begins at maximum tillering in all rice cultivars.
· Flowering occurs in all cultivars about 30 days after panicle initiation.
· The young panicle (panicle primordium) becomes visible (with a magnifying lens) within
o 40-45 days of seeding in cultivars maturing in 95-100 days.
o 50-52 days of seeding in cultivars maturing in 105-110 days.
o 60-62 days of seeding in cultivars maturing in 115-120 days.
o 65-70 days of seeding in cultivars maturing in 125-130 days.
Gibberellic acid application
· Gibberellic acid can also be written as GA3.
· We spray hybrid rice seed production plots with GA3 to:
o adjust plant height of both parents.
o increase the growth rate of secondary and tertiary tillers so that they bear panicles.
In the seed parent, GA3:
· enhances panicle exertion from the flag leaf.
· increases the duration of floret opening.
· increases the rate of stigma exertion and lengthens the duration of stigma receptivity.
· Supplementary pollination is artificially shaking the canopy of the pollen parent at flowering to increase cross pollination.
· Supplementary pollination
o causes anthers to shed all of their pollen.
o disperses pollen grains uniformly over the seed parent plants.
o increases seed set in the seed parent.
· Supplementary pollination is done by
o two persons pulling a 1-cm diameter rope across the two R lines.
o one person stirring the canopy layer of the R lines with a bamboo stick, taking care not to break off the panicles at the neck.
Roguing
· Roguing is the removal of undesirable rice plants from hybrid seed production plots.
· Undesirable rice plants are plants in either the A line or R line rows that differ from plants that are true to type. They may be volunteer plants from an earlier crop or off-types.
· Roguing prevents off-types from cross pollinating with true-to-type A line plants and lowering the purity of the hybrid seed.
· Roguing ensures that the hybrid seed produced will be a cross between only the A line and R line parents. That in turn ensures that the commercial plantings of the hybrid seed produced will give high yields.
· High purity hybrid seed will increase your reputation as a seed grower.
· Roguing can be done at any time of the crop stage. Off-type rogues can be removed from the crop whenever they appear.
· The most important stages for roguing are:
· at maximum tillering.
· at flowering.
· just before harvest.
At maximum tillering
· Remove any plants outside the rows.
· Remove plants that are considerably taller or shorter than the seed or the pollen parents.
· Remove plants that are off-type in leaf blade size or shape.
· Remove plants that are off-type in color of the leaf sheath or leaf collar.
·
At flowering
· Remove off-type plants that flower very early or very late.
· Remove plants that are off-type in leaf size, leaf angle, and panicle shape and size.
· Remove plants from the A line that have plump, yellow anthers and shed pollen. Plants in the A line should not have viable pollen.
· Remove plants with fully exserted panicles from the A line.
· Remove all diseased plants from the seed production plot.
Before harvest
· In A line rows, remove plants that have normal seed set.
· Remove off-types that have different grain characters from the normal A line plants. Look for differences in grain shape, grain size, or the presence or absence of awns.
Harvesting
· Harvesting hybrid rice seed production plots is different from harvesting a rice grain crop.
· Harvest the R line first, and then harvest the A line.
· The A line harvest is the only one that can be sold as hybrid seed. The R line harvest may be sold as grain or kept for home use.
· The A line harvest and the R line harvest must be kept separate from each other during harvesting, threshing, drying, and bagging.
· Harvest when 90% of the grains in the main panicles of the A line plants are clear, firm, and straw colored. The rest of the grains should be in the hard dough stage.
· Harvest when seed moisture is less than 20%.
· Drain the hybrid seed production field 7-10 days before expected harvest. Draining the field makes the crop mature faster and helps to achieve uniform maturity in the crop.
· Harvest all B or R line rows first.
· Harvest the plants manually by cutting them off at the base with a sickle or scythe.
· Remove the R line harvest and store it in a safe place for threshing later.
· Do not leave even one panicle in the field. It could be mixed with the A line harvest and reduce the purity of the hybrid seed.
· Rogue the A line rows one more time before harvest.
· Remove plants with normal seed set.
· Remove any other plants that appear to be off-types
· The A line can be harvested manually or with a mechanical combine. If a combine is used, it should have adjustable field speed and clearance to prevent field loss or grain damage.
Threshing
· During threshing, the seed parent and pollen parent harvests must be kept separate from each other. The seed parent should not get mixed with other seed or grain on the threshing floor or with any leftover in the thresher.
· All threshing equipment and the threshing floor should be thoroughly cleaned before starting threshing.
· New jute sacks should be available for bagging the seed.
· If new sacks are not available, then use clean used sacks. The used sacks must not contain any rice grains that could become mixed with the hybrid seed.
· Make two labels for each bag: one to place inside the bag and one to attach to the outside.
· Each label should contain the following information:
o your name and address.
o the name of the hybrid.
o the location of the seed production field.
o season.
Threshing the seed parent:
· Thresh the seed parent first to keep it from being mixed with any other seed.
· Thresh the seed manually with a hand flail on a threshing floor or with a manual or power-driven thresher.
· Dry the threshed seed of seed parent immediately.
Threshing the pollen parent:
The pollen parent should be threshed separately and used as grain. It should not be used as seed.
Seed Drying
· Seeds can be safely stored when they have been dried to a moisture content of 13%.
· Drying helps seeds maintain their ability to germinate and their vigor for a longer period.
· Drying controls mold growth and the activity of other organisms that reduce the quality of stored grain.
· Drying reduces seed discoloration, which lowers the market value of the seed
· Seeds can be sun-dried on a threshing floor.
· Do not dry the seeds directly on the concrete threshing floor. Place them on jute bags or on a tarpaulin.
· Stir the seeds occassionally to ensure uniform drying.
· Seeds can be dried in a batch-type dryer by forced air heated to 40- 45 °C.
· Do not dry the seeds abruptly to 13% moisture content if the beginning seed moisture is higher than 20%.
· The seed layer in a batch-type dryer should not be more than 45 cm deep.
Processing Hybrid Rice Seed for Market
The purpose of cleaning the seed is to:
· Remove impurities such as trash, leaves, broken seeds, sand or grit, etc.
· Remove weed seeds or those of other plant species.
· Remove immature, shriveled, unfilled, and empty spikelets.
· Seed can be cleaned manually by winnowing. Winnowing removes only light, chaffy material.
· An air screen machine not only cleans the seed but separates seed of uniform size from oversize and undersize seeds. The process of separating seeds of uniform size is known as grading.
· Air screen machines are normally too expensive for on-farm ownership. Cleaning and grading are usually done by public or private seed agencies that contract with seed growers for hybrid seed production.
· Before seeds can be packed and sold as hybrid seed, they must be tested for germination rate and purity.
· Public seed testing agencies normally do the testing and certification. The germination rate must be at least 85% in order for seed to be certified.
· Before taking your seed for testing, you can do your own germination test at home by following the instructions.
1. Spread 200 seeds evenly over new or clean jute sacks that have been soaked in water.
2. Cover the seeds with another wet jute sack.
3. Roll up the jute sacks with the seeds inside and store them in the shade for 7 days. Keep the rolled sacks moist for the entire period. Do not let them dry out.
4. Make three sets of 200 seeds.
5. At the end of 7 days, count the normal seedlings that have developed. (Normal seedlings will have well-developed roots and shoots.)
6. All three sets of germinated seeds should have a germination rate of at least 85%. A germination rate of 85% is 170 normal seedlings for each set of 200 seeds.
· If the germination rate of your seeds is 85% or higher, the seeds can be packed.
· Pack your seed in clean, preferably new, jute bags.
· If you store your seeds in used bags, you should disinfect the bags to protect the seed from insects that could attack the seed during storage.
· Follow these steps to disinfect used bags.
1. Turn the bags inside out and shake them thoroughly so no seeds of any kind stick to the inside of the bag.
2. Soak the bags for 10 minutes in a 0.15% solution of malathion. (Make the solution by mixing 1 part malathion 50 EC in 300 parts water.)
3. Dry the bags under shade before filling them with seed.
· Do not pack your seed if the moisture content is more than 13%. The seed could spoil during storage.
· Make two labels for each bag - one to place inside the bag and one to attach to the outside.
· Each label should contain the following information:
1. your name and address.
2. the name of the hybrid.
3. the location of the seed production field.
4. season.