At the current rate of population growth in India, the
requirement of rice by the turn of century is estimated to be around
150 million tons.
To make the India self sufficient in rice, it is needed
to improve the productivity to a greater extent.
The task is quite challenging and the options available
are very limited.
Among the various possible genetic approaches to achieve
this target, hybrid rice technology is the most feasible and readily
adaptable one
Commercial success of hybrid rice in China has clearly
demonstrated the potential of this technology to meet the ever-increasing
demands for rice world over.
Efforts to develop and use this technology in India,
though initiated in 1970’s, have been systematized and intensified since
December 1989, with launching of a mission oriented project.
Within a short span of seven years, half a dozen hybrids
each from public and private sectors are made available for commercial
cultivation.
Some more promising hybrids with better grain quality,
resistance to some of the major pests and diseases and higher magnitude
of heterosis are in final stages of evaluation.
Hybrid seed production technology has been developed
and demonstrated on large scale and an average seed yield of 1.0 -–1.5
t/ha is being obtained on large scale.
During the dry season 1995-96, totally around 1300 tons
of F1 seed was produced by private and public sector seed agencies.
During the wet season 1996, more than 60,000 hectares
were planted to hybrid rice in various parts of India.
Achievements Through Hybrid Rice
Hybrid rice has helped china to increase rice production nearly by
200 million tons from 1976-1991.
Hybrid rice has yield advantage of more than 30% over conventional
varieties.
The area under hybrid rice was 17.6 million hectares i.e. 55% of total
rice area in china and the production of hybrid rice was 66% of the
total rice out put.
Although research on the commercial utilization of heterosis in rice
has made tremendous gain during the last 20 years, it is from a strategic
point of view, that the high yield potential of hybrid rice has not
been fully tapped yet.
Average yields of hybrid are more when compared to high yielding varieties.
Quantity of seed used in hybrid rice was significantly less than the
seed used in conventional high yielding varieties.
Average productivity and total return to total input cost was relatively
higher for hybrid rice than for conventional high yielding varieties.
Hybrid rice cultivation is economically viable if management level
is above 60 per cent.
The nursery area required for transplanting unit area is less when
compared to conventional high yielding varieties.
Hybrids are short duration with resistance to major pests and diseases.
Hybrids are non-lodging varieties.
Disadvantages
Management responsiveness was nearly 30 – 35 % more for hybrid rice
than for conventional high yielding varieties.
At an average management level, the grain yield of hybrid (0.8 t/ha)
was lower than the minimum required (1.4 t/ha).
Seed cost was almost 2.5 times more for hybrids than for conventional
high yielding varieties.
The expected output price was lower for hybrid rice grain than actual
price for conventional high yielding varieties.
The hybrid rice seed production usually requires more labour specially
to accomplish certain critical farm operations like row planting, supplementary
pollination, leaf clipping, gap filling, rouging and GA3
application etc. Hence the cost incurred on seed production was found
to be high.
For economic feasibility and commercial viability of
rice hybrid technology, development of an efficient and economic seed
production package is a pre-requisite.
Hybrid rice seed production involves several technical
skills, which have to be managed successfully to obtain an acceptable
yield level of 1.0 to 1.5 tons/ha.
Some of the aspects, which need to be standardized
in hybrid rice seed production, are as follows:
Obtaining proper synchronization of flowering between
two parental lines,
Determining optimum row ratio,
Factors promoting out-pollination rate,
Appropriate dose and stage of GA3 application,
Precise timing and frequency of supplementary pollination.
Effective rouging at right stage to maintain high
purity.
Careful and meticulous handling during harvesting,
processing and packing.
At present two approaches, viz.,Three line system
and Two line system are being followed in India for heterosis
breeding in rice.
Three line system
There would be need to produce three lines namely,
Cytoplasmic male sterile line,
Maintainer line (or) B-line, and
Restorer line (or) R-line.
Two line system
B-line production is not needed.
The optimum package for hybrid seed production
and CMS multiplication is given below,
Activity
Particulars
Seed rate
Seed parent 15 kg/ha,
Pollen parent 5 kg/ha
Nursery
Sparse seeding to ensure multi-tillered (M-5)
seedlings in 25 days.
Row ratio
2B : 6A, for CMS multiplication, 2R : 8A,
for hybrid seed production.
Number of seedlings/hill
Two seedlings/hill for seed parent,
Three seedlings/hill for pollen parent.
Spacing
B/R to B/R 30 cm B/R to A 30 cm
A to A 15 cm
GA3 application
45 g/ha at 5.0 % heading in two split doses
on consecutive days
Supplementary pollination
Twice a day at peak anthesis during flowering
phase.
Rouging
During vegetative phase based on morphological
characters and twice during and after flowering based on floral
characters etc.
Seed yield
1.5 – 2.0 tons per ha
Two line method or PGMS and TGMS System
Chinese rice scientists have been explored new technological
approach to replace the CMS System and raise the yield ceiling claims
in hybrid rice.
So far the most successful is the development of 2-line
method hybrid rice.
The method is based on the 2 new kinds of rice genetic
tools viz., Photosensitive (PGMS) and Thermo-sensetive (TGMS) genetic
male sterile lines which have been developed successfully in China.
Male sterility is mainly controlled by 1 or 2 pairs
of recessive nuclear genes and has no relation to cytoplasm.
The advantage of the system over the above(CMS)
Maintainer lines are not needed. The PGMS lines( under long day length)
and TGMS lines( under high temperatures) show complete pollen sterility
and can thus be used for hybrid seed production. Under shorter day length
or temperate conditions, they show almost ,normal fertility and can
be multiplied by selfing.
Choice of parents for development of heterotic hybrids is greatly
broadened. Studied showed that more than 98% of varieties tested can
restore such male sterile lines.
In addition, thePGMS and TGMS genes can be transferred easily to almost
any rice lines with desirable characteristics.
Therefore no negative effects due to sterile cytoplasm and the unitary
cytoplasm situation of WA will be avoided.
Hybrid Rice
