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.
Ikisan - Advantages And Disavantages Of Hybrid Rice
Advantages AND Dis-advantages
Advantages
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
