New genetic techniques to introduce disease-resistance and other traits in banana plants
TWO groups of scientists have developed
techniques to genetically alter banana
(Musa species) cells to make the plant
disease- resistant and introduce other
improvements in it. This is significant
when one considers that
in some areas of the
world up to half the
banana yield is lost to
fungal and viral diseases genes into
and to pests.
While a group of
Belgian scientists reports
2 techniques to develop
transgenic (containing
foreign genetic material
besides its own) bananas
with high resistance to Steel filter
insects, viral diseases and
fungal pathogens, another group of researchers
has demonstrated how
foreign genetic material
with favourable traits can - Adjustable
be incorporated into the
plant using a bacterium
(Biotechnology, Vol 13, No 5).
Banana is the staple food for
almost 400 million peopl6'worldwide
(that's nearly half the population of
India). Its global production of 76 million tonnes makes it the fruit crop
with the highest yield in the world.
About 10 per cent of the world's banana
production generates large revenues to
the tune of over us $4 billion through exports.
Even though banana contributes to
both food security and export revenues
in developing countries, the production
of the crop is totally depenclant on
plant-clones that are collected in nature,
domesticated and then maintained by
clonal propagation. The crop has never
benefited from traditional crop breeding methods.
Conventional breeding methods to
develop improved varieties are not used
to produce disease- resistant bananas
because the techniques require as long
as 10 years to bear results. Besides, most
edible banana varieties are sterile
because the plant is a triploid (having 3
sets of chromosomes. Hence, they can-
not pair and this causes sterility). In
order to transfer genes into the banana
plant, an efficient genetic transformation method and regenerabie tissues are
required - both the conditions have
now been met.
The techniques developed by Laszlo
Sagi from the Laboratory of Tropical
Crop Husbandry, Catholic Univers
Leuven, Belgium, and colleagues exploit
the recent setting up of regenerable
embryogenic cell suspensions (ECSS) Of
banana. ECSS of banana are solutions of
liviiig banana cells from which a plant
can be developed.
The first method uses high voltage
electric fields to inject foreign genetic
material into banana ECSS. This method
enables avoidance of chimerism - the
occurrence of genetically different tissues in the same organism - which is a
frequently observed phenomenon in transgenic plants.
The second method is the particle
bombardment technique which uses a
helium-driven gun to shoot foreign
genes which code for several antifungal
proteins and are obtained from the
seeds of different plant species, into ECS
targets. The antifungal proteins that the
foreign genes code for are harmless to
both the banana cells and humans. The
major fungal diseases that strike banana
crops are Black Sigatoka, which is
caused by Mycosphaerella fijiensis, and
Panama disease for which the causal
agent is either Fusarium oxysporurn or cubense.
The Belgian scientists had specially
designed a particle gun for their experiments. The target plant cells were placed between nylon meshes and then sandwiched between a Pvc pipe and a table
whose height could be adjusted. Different lengths of Pvc pipes were used on
different target cells. The particle bombardment technique has been perfected
in the case of banana and has proved
simple, inexpensive and efficient.
In another development, a team of
scientists under a joint project of the
Food and Agriculture Organization and
the International Atomic Energy
Agency, has used a bacterium called
Agrobacterium to induce foreign genes
into banana cells. The team, led by
Gregory D May of the Institute of
Biosciences and Technology, Texas A&M
University, Houston, cultivated banana
tissue samples with the Agrobacterium
for 4 weeks and found that the banana
cells had incorporated the foreign genes.
This method, the scientists claim, could
be used to introduce value-added traits
into the banana plant.
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