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Breeding And Crop Improvement
- Breeding banana is almost a difficult exercise due to complexities
resulting from parthenocarpy, sterility, polyploidy and vegetative propagation.
The uniqueness lies in the fact that in banana which is almost sterile,
raising sexual progeny in sufficient numbers to combine desirable characters
and at the same time resulting in another sterile plant is indeed very
difficult.
- As the degree of sterility is particularly high in edible cultivars,
breeding banana is complicated, difficult and time consuming. Nevertheless,
the results of work done since 1922 in the West Indies proved to be,
in the words of some, an encouraging milestone of success.
- The sole objective of banana breeding in the West Indies was to evolve
a banana as like Gros Michel as possible but immune or highly resistant
to Panama wilt disease. Gros Michel had been the only main commercial
banana (the green gold of Jamaica) at that time (though in the subsequent
years Lacatan, Highgate, Cocos and Valery gained importance) with all
the desirable characters, but it became almost impossible to grow it
on account of its high susceptibility to the wilt disease, for which
there was and still, is, no effective chemical or cultural method of
control except by growing resistant cultivars.
- The first artificially produced hybrid banana in the West Indies,
named IC-1was a tetraploid and was highly resistant to Panama disease.
- It was evolved by crossing Gros Michel (AAA) with a wild wilt resistant,
seeded diploid M.acuminata spp. malaccensis. Its bunches
lacked symmetry and, hence, were not suitable for shipping as naked
bunches.
- Besides, the fruits were shorter and the number of hands were also
fewer per bunch. Other hybrids IC-2, S-19, J-1877 and Bodles Altafort
produced subsequently were also similarly unacceptable.
- The latter had several desirable qualities, but its tall stature and
slow growth with leaves often breaking at the base proved unsuitable
for the cyclone prone islands.
- In the beginning, the breeders were trying to exploit Gros Michel's
ability to form a few unreduced triploid egg cells that could be fertilized
with normal haploid pollen to give tetraploid embryos.
- The value of this phenomenon was that genes from the mother plant
did not segregate and, therefore, the maternal characteristics in respect
of the fruits were retained.
- Adding one set of chromosome from a diploid, carrying heritable resistance
to wilt to the three sets from the mother was the main idea in this
programme.
- This had the undesirable effect of restricting breeding to a parent
that was highly susceptible to the disease, besides, being tall in stature.
Another possibility was then to breed triploids by crossing these tetraploids
with diploids.
- This involved the usual processes of reduction division on both sides,
reassortment and seggregation of gene complexes, giving only a remote
chance of success, as practice has confirmed.
- Numerous primary tetraploids and secondary triploids have now been
bred in this way.
- The objective of banana breeding in India is entirely different. Unlike
West Indies, banana cultivation in India is polyclonal and Panama wilt
never became a threat.
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Hybrid-95,
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- Breeding work started in Tamil Nadu in 1949, therefore, had
the objectives of improving the bunch grade, reducing the stature
of the plant, etc.
- Hybrids that resulted from the preliminary work carried out
with 15 triploid cultivars and four other species of Musa including
balbisiana were found inferior.
- In the meantime, nematodes became serious problem.
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Hybrid-21.
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- The programme was, therefore, reoriented to include some of
the commercial edible diploids already in cultivation, in the
breeding programme.
- As many as 13 acuminata (AA) and 10 hybrid (AB) diploids
were screened and two of them, Anaikomban (AA) and Tongat (AB)
were found fairly resistant to nematodes.
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- Another diploid-Sanna Chen Kadali (AA) having a red fruit skin was
selected for its hardy nature, medium tall stature, shorter duration
and resistance to leaf spot disease. A synthetic diploid (AA) evolved
by crossing Matti (AA) and Pisanglilin (AA) has the high fruit quality
of the former and nematode resistance of the latter.
- This new diploid has great potential to serve as a male parent in
the future breeding programme.
- A new triploid hybrid H-135 (AAB) evolved through multiple crossing
involving M.balbisiana is becoming popular as it resembles the
famous Virupakshi hill banana of Tamil Nadu both in respect of high
fruit quality and external appearance.
- Some reported a new banana clone UCRS as resistant to Mycosphaerella
musicola and also resistant to wind damage. The plant adapts well
to various types of soil.
- In a trial to determine the acceptability to the British customer,
34 clones were assessed by taste palels. The acceptability varied considerably,
but the best clones were comparable with established Cavendish clones,
such as Valery.
- The cultivars obtained from IITA, Nigeria showed good drought, pest
and disease and wind resistance in Bangladesh. The cv. Ogonired gave
the highest yield.
- Most breeding efforts have been directed towards the improvement of
dessert bananas, the greatest consideration being fruit quality, dwarfness
and disease resistance. Resistance to important disease, such as fusarium
wilt, Sigatoka leaf spot, black Sigatoka and resistance to the burrowing
nematode (Radopholus similis) have been by far the main recent
breeding objectives, and these, in turn, have necessitated a continued
search for germplasm and an interest in the origin of various cultivars
and clones.
- Modest programmes have been initiated to explore the use of induced
mutation breeding. As a purely clonal crop plant, it seems that bananas
are admirably suited to this approach.
- It is quite clear that the effects of somatic mutation or bud sporting
can be significant, since from a historical perspective in Jamaica alone,
some six mutants of the once highly prized Gros Michel were detected
in a 100-year period, and it is surmised that many more have gone undetected.
- Improvement by mutations induced by chemical mutagens of irradiation
has great potential, which needs further investigations.
- Callus and cell culture, somatic embryogenesis, androgenesis and related
techniques for Musa improvement pointed out that genetic engineering
procedures, such as gene insertion, perforce will depend on successful
regeneration of the plant from cells and protoplants.
- Even procedures involving pollen genome modification will benefit
from such capability, and screening embryoids from pollen will require
androgenesis to be achievable at a reasonably high efficiency.
- All perspective advantages that might accrue to banana-plantain breeding
or improvement programme other than the obvious ones, such as embryo
rescue and multiplication via meristems and shoot tips demand availability
of dependable cell, protoplast, anther-pollen-ovule culture procedures.
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