Hybrid- Rice Seed Production Technology (Three –Line System)
In the years to come location- specific specialised 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 of seed production should be chosen so as to provide the best possible conditions at flowering and the pollen shedding period. The most suitable condition are, 24-28 0C day light average temperature, the relative humidity 70-80 percent , the temperature difference between day and night 8-10 0 C and good sunshine. An average day temperature of more than 30 0C or less than 230C, 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 glues 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 levelled, should have fertile soil with good physical and chemical characteristics and well drained.
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 and R line Production) and by 100 meters for hybrid seed production ( AX R production).
4) Brief Cultural Practices for hybrid (AXR) Production Nursery:
Raising of vigorous 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 dry matter is accumulated, leading to 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 100-150 kg/ha for the male parent. At present the appropriate methods for raising seedlings are either to sow under plastic film in the field or in a green house.
5) 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.
Seedlings 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.
7) Planting Ratio:
The ratio of female and male lines is generally kept at 2:10-12, and row spacing 10X10 cm for male parent and 20X 15 cm for female parent. Two seedlings are planted per hill.
8) Row Difference:
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.
Adequate fertilization in necessary. In general a seed field with moderate fertility should be treated with 200 kg N, 50 kg P, and 150 kg K per ha, 90 percent applied as a basal dose and 10 percent after panicle differentiation.
10) 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 drained the booting stage. During heading, if the air temperature is above 35 0 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.
11) Synchronization of Flowering :
Synchronizing the flowering of both parents is the key to increased yields. Technical measures such as staggering seedling dates of the male and females 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 for each hybrid and the locations selected for the hybrid seed production.
i) Staggered Sowing of Male Parents:
Seedling 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 . The second 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 or 4 random samples of the main culm of both parents are taken 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 dihydrogen 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.
Methods of Improving Seed Setting:
i) Supplementary Pollination ( Rope Pulling) :
On calm days during anthesis, supplementary pollination can be carried out. Panicles of the restorer lines are shaken by pulling a long nylon rope ( 5mm diameter) back and forth every 30 minutes until no pollen remains on the restore line. This method if often used on even topography and regularly shapped 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 out crossing 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 help increased seed setting.
The seed field should be free of rogues. Remove off- type plants in both the parents first before the onset off 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.
iv) Harvesting of Seed Crop:
Harvest male rows first to avoid chances of mechanical admixture.
v) Seed Yields: