This article is an extention of our previous article written by Dr. Vivek Kumar Singh. We suggest you to read the previous article to understand this knowledge piece in a better form.
Selection of land
The land selected for seed production should be fertile, preferably light-textured, with adequate irrigation and a proper drainage system. The field should be free from weeds and volunteer plants from the previous paddy crop. In order to achieve synchronous flowering, a homogenous plot with an even topography is required. The field should not be infested with serious pests and diseases. Hybrid rice seed production fields should be isolated as rice pollen can travel longer distances with the wind; negligence leads to impurity of F1 seed. When selecting for isolation of land, the following points must be considered:
Space isolation: Space isolation of at least 100 m from seed production plots to other rice varieties is normally satisfactory for quality hybrid seed production. It is safer to have an isolation distance of up to 200 m for male sterile (A line) multiplication, while for B and R line multiplications in varieties, an isolation distance of 3 to 5 m is sufficient.
Time isolation: When space isolation is not possible, time isolation of about 30 days is satisfactory. This means that the flowering stage of the parental lines in the seed production field should be at least 30 days earlier or later than that of other varieties grown within the area to avoid contamination by pollen.
Barrier isolation: Tall and compact trees or bushes or some tall crops (e.g. sorghum, pigeon pea and sugar cane) with 30-40 m distance can serve as barrier isolation.
Space isolation is the most important factor to be considered for the production of quality seed.
Picture of Isolation Distance Seeding time
Seeding of the parental lines should be planned in such a way that flowering coincides with the most favorable climatic conditions listed below:
Daily mean temperature of 24°-30°C
Relative humidity of 70-80%
Differences between day and night temperature of 8°-10°C
Sufficient sunshine with moderate wind velocity
No 3 days’ continuous rain during flowering period
These conditions are well met in the dry season.
Nursery bed preparation and sowing
Given the high cost of seed, it is essential to raise the nursery in a well-managed field if healthy and robust seedlings are to be obtained. Optimum seed rate should be applied and every seed must be utilized by adopting good nursery management practices. A sparse well-managed nursery gives healthy seedlings for the main field. The normal recommendation is 1 kg of parental line seed in an area of 40 m2. For 1 ha of main field, 12.5 kg of A line seed and 5 kg of R line seed are required.
Picture- Nursery Bed.
Staggered sowing of parental lines for flowering synchrony
Hybrid seed set on the female line depends primarily on its flowering synchronization with the R line; the sowing of male and female lines must therefore be planned to achieve this. For example, if the duration of the male line is 10days more than that of the female line, the male line is sown in 2-3 staggered sowings so as to ensure a continuous pollen supply. In such cases, 3 sowings of the R line (i.e. 13, 9 and 5 days ahead of the female line) are carried out. However, in countries such as China where the technology has been perfected, only 1 or 2 sowings of the male line are necessary.
Conventional high-yielding varieties may be transplanted once the nursery crop is 25-30 days old; but in hybrid seed production plots transplanting may commence (depending on the difference in duration of the A and R lines) when 21-35 days old. Timely transplanting ensures good picking of parental lines. Transplanting of too young or very old seedlings may either delay or accelerate flowering and affect tiller number.
While pulling out the nursery and during transplanting, special care should be taken to avoid mixing seedlings of male and female parents. It is also important to avoid mixing seedlings of different ages of the male parent, which could affect the uniform distribution and availability of pollen. The long- duration parental line must be transplanted first in order to obtain good synchronization at flowering.
Transplanting R lines
Paired rows with 15 cm spacing between plants.
Seedlings of different ages transplanted in a sequential order (e.g. I, II, III, then again I, II, III).
Single seedlings per hill with row-to-row spacing of 15 or 30 cm (as per recommendation) in the main field.
Transplanting A lines
Six rows with 15 cm spacing between the paired rows of R line seedlings is the normal recommendation in many Asian countries.
One seedling per hill with a spacing of 15 x 15 cm.
In India, spacing of 30 cm between A line and R line rows to facilitate bumper male growth and supplementary pollination. In China, A: R row ratio varies from 2: 8 to 2: 14.
Row ratio, spacing and direction
Years’ experience in hybrid rice seed production indicates that row ratio and spacing play a major role. Seed parents and pollen parents planted in a specific row ratio and with specific spacing have a marked effect on seed yields. A row ratio of 6: 2 seed parent to pollen parent has proven very effective. Row direction perpendicular to the prevailing wind direction at flowering stage allows easy pollen dispersal on the seed parent.