The successful development and use of hybrid rice technology in china during 1970’s led the way for development and release of rice hybrid varieties elsewhere. India has made good progress in this regard and it is expected that hybrid varieties of rice shall be soon available for cultivation to the Indian farmers.

  Hybrid-rice can be produced in the following ways.

1. Three-line system : The hybrid seed production involves multiplication of cytoplasmic-genetic male sterile line(A line), maintainer line (B line) and a restorer line (R line); and production of F1 hybrid seed (AxR)
2. Two-line system: The hybrid seed production involves the use of photo-period sensitive genetic male steriles(PSMS).  Any normal line can serve as a restorer.
3. By using chemical emasculators: Chemicals that can sterilize the stamen, with little or no effect on the normal functioning of the pistil, can be used to emasculate female parents for hybrid rice production.  The advantages are obvious, no special development of male sterile or restorer lines is required, and extensive varietal resources are available. Chemical emasculators such as male gametocie 1(MF1) and male gametocie 2(MG2) were developed inChina and have been successfully used in hybrid rice production. In chemical emascultion, physiological male sterility is artificially created by spraying the rice plant with chemicals to induce stamen sterility without harming the pistil.  In hybrid seed production, two varieties are planted in alternate strips, and one is chemically sterilized and pollinated by the other. 

In the years to come location-specific specialized seed production technology for the released/commercial hybrids would have to be developed for obtaining maximum seed yields and ensuring good seed quality.  Good crop management is necessary for raising a hybrid-rice seed production crop.  Hybrid-rice production technology described below may be used as a guideline.

1. Choice of areas and Growing season for seed production:  the areas ofseed production should be chosen so as to provide the best possible conditions at flowering and the pollen shedding period.  The most suitable conditions are, 24-28 C day light average temperature, the relative humidity 70-80 per cent, the temperature difference between day and night 8-10 C and good sunshine.  An average day temperature of more than 30 C or less than 23 C, continuous rains, or strong wind are generally harmful to flowering, pollination and cross –fertilization.  As a rule, in high temperature with low humidity or in low temperature with high humidity some glumes will not open.  This lowers the seed yields. The growing of hybrid seed crop should be so adjusted that flowering takes place after the end of high temperature period, but before the start of low temperature period.

2. Selection of seed fields: The selection of prime field plots is necessary.  The seed fields should be free of volunteer plants, well leveled, should have fertile soil with good physical and chemical characteristics, and well drained.
3. Isolation: the hybrid paddy fields should be isolated from the other paddy fields, including commercial hybrid of same variety; and same hybrid not conforming to varietal purity requirements for certification at least by 200 meters for foundation seed class (A, B & R line production) and by 100 meters for hybrid seed production (AxR Production)
4. Brief Cultural Practices for hybrid (AxR) production Nursery.  Raising of vigourous seedlings is an important factor for obtaining high seed yields. The root system of vigorous seedlings are flourishing , leaf sheaths have high carbon content and all this contributes to produce green growth and tillering at the lower nodes so that more panicles  and a high seed setting rate per panicle.  It has been observed that tillering at the lower nodes gives more and bigger panicles which helps to achieve the goal of 100 kernels per ear.

Prepare the seedling bed with basal manure.  Seed at 150 kg/ha for the female parent and 110-15- kg/ha for the  male parent.  At present the appropriate methods for raising seedlings are either to sow under plastic film the field or in a green house. 

Sowing time: The proper sowing time is dictated by the number of days required from sowing time to panicle formation.  The sowing should be so adjusted that the crop comes to panicle stage soon after the end of high temperature period.

Transplanting: seed lings with healthy tillers are the basis for increased panicle size.  For hybrid seed production, the seedlings of both parents should be standardized.  Seedlings of the male parent for short duration varieties should be 20-30 days old with 5.5-7 leaves  and 2-3 tillers and for long duration varieties 30-35 days old with  5.5-7 leaves and 2-3 tillers.

Planting ratio: The ratio of female and male lines is generally kept at 2:10-12; and the row spacing 10x10 cm for male parent and 20x15 cm for female parent.  Two seedlings are planted per hill.

Row direction: both parents should receive good aeration and equal amounts of sunlight.  Row direction should be nearly perpendicular to prevailing winds at flowering to ensure more cross-pollination.

Fertilization: Adequate fertilization is necessary.  In general a seed field with moderate fertility should be treated with 200 kg N, 50kg P and 150kg K per ha; 90 per cent applied as a basal dose and 10 per cent after panicle differentiation.

Water management:  Good water management is very important for regulating water, fertilizer, air and temperature of soil.  Give shallow irrigation at the transplanting and tillering stages.  In soils where water  permeability is poor the field must not be allowed to remain under water for too long so that root growth could be encouraged.  During the middle stages thewater should be drained off properly.  Shallow water must be maintained again during the booting stage.  During heading, if the air temperature is above 35 C, water should be applied during the day and drained-off at night so as too decrease soil temperature.

Other cultural practices are the same as described for conventional (open pollinated) varieties

Synchronization of flowering: Synchronizing the flowering of both parents is the key to increased yields.  Technical measures such as staggering seeding dates of the male and female parents, sowing the male  parents three times to extend the time pollen  is available, and predicting and adjusting flowering dates may be adopted.  Actual practices would have to be standardized foreach hybrid and the locations selected for the hybrid seed production.

(i)                  Staggered sowing of male parents: Seeding date is usually determined by leaf age, effective accumulated temperature (EAT), and growth duration.  In general, the period from initial to full heading of a CMS line is 4-6 days longer than for a restorer line.  The first sowing of the male parent establishes the dates for second and third sowing.  The second sowing is done when the leaf emergence on the first sowing is 1:1; the third sowing when the leaf emergence is 2.1.  Thesecond sowing is the main parent.  The planting ratio for sowing at different dates is 1:2:1.

(ii)                By fertilizer application.  Beginning about 30 days before heading, 3 or4 random samples of the main culm of both parents are tekn every 3 days.  Young panicle development is compared under magnification. During the first three stages of panicle differentiation, treat the earlier developing parent with quick releasing N fertilizer; and spray the later developing parent with potassium di hydrogen phosphate.  This adjusts development differences of 4-5 days.

(iii)               By water management;  During later stages of panicle differentiation, draining water from the field will delay male parent panicle development, higher standing water will speed panicle development.

(i)                  Supplementary Pollination (Rope pulling). On calm days druign anthesis, supplementary pollination can be carried out.  Panicles of the restorer lines are shaken by pulling along nylon rope (5 mm diameter) back and forth every 30minutes until no pollen remains on the restorer line.  This method if often used on even topography and regularly shaped plots.  In hilly, uneven topography with small, irregular plots, a bamboo pole may be used.

(ii)                Leaf clipping; Leaves taller than the panicles are the main obstacles to cross pollination.  Clipping leaves 1-2 days before initial heading increases the probability of pollination and outcrossing rate.  The blade of flag leaf is cut back ½ to 1/3 from the top.

GA3 Spray.  Spraying seed parent with 75 gm  GA3/ha 60 ppm or more 2 or 3 times increases panicle exsertion and helps increased seed setting.

Roguing: The seed field should be free of rogues. Remove off-type plants in both the parents first before the onset of flowering stage and then soon after emergence of the panicle. Rogue out the plants of maintainer line, if any and the semi-sterile plants in the seed parent as often as necessary.

Harvesing of seed crop: Havest male rows first to avoid chances of mechanical admixture.

Seed yield 5-15 Quintals/ha.