Horticulture is science concerned with intensively cultivated plants that are used by
people for food, for medicinal purposes, and for aesthetic gratification. Horticulturists apply the knowledge, skills, and technologies used to grow
intensively produced plants for human food and non-food uses and for personal
or social needs.
Biotechnology
is broadly saying, any technique that uses live organisms like bacteria,
viruses, fungi, yeast, animal cells, plant cells etc. to make or modify a
product, to improve plants or animals or to engineer micro-organisms for
specific uses.
It is concerned with upgradation of quality and also utilization
of livestock and resources for the well-being of both animals and plants.
Biotechnology
in Horticulture
Biotechnology
offers a vast potential in horticulture. The biotechnological tools may likely
to have greater impacts in horticulture, where even minor changes such as in color,
aroma quality and postharvest behaviour would make significant commercial
impacts Genetic transformation, micropropagation, in vitro conservation of
germplasm, synseed technology, virus-cleaning, biofertilizers, biopesticides
and postharvest biotechnology are important areas in biotechnology of
horticultural crops.
Horticultural scientists study crops that are used
for food, drugs, or aesthetics. Many of these crops are unique or so highly
specialized that they are no longer propagated sexually by seeds but rather
asexually by such methods as cuttings, grafting, layering, and tissue culture.
Seedless grapes, potatoes, maple trees, and roses are some examples of crops
that are propagated by some or all of these methods. Although some cultivars
are very well known and widely grown, problems related to disease
susceptibility, fruit or flower quality, or growth habits arise occasionally.
Applications of Biotechnology in Horticulture
The major areas of
biotechnology which can be adopted for improvement of horticultural crops
are:
1. Tissue Culture
One of the
widest applications of biotechnology has been in the area
of tissue culture and micro propagation in particular. It is one of
the most widely used techniques for rapid asexual in vitro propagation. This technique is economical in time and
space affords greater output and provides disease free and elite
propagules. It also facilitates safer and quarantined movements of
germplasm across nations.
When the traditional
methods are unable to meet the demand for propagation material this technique
can produce millions of uniformly flowering and yielding plants.
Micropropagation of almost all the fruit crops and vegetables is possible
now. Production of virus free planting material using meristem culture
has been made possible in many horticultural crops.
Embryo Rescue
It is another area where
plant breeders are able to rescue their crosses which would otherwise
abort. Culture of excised embryos of suitable stages of development can
avoid problems encountered in post zygotic incompatibility. This
technique is highly significant in intractable and long duration horticultural
species. Many of the dry land legume species have been successfully
regenerated from cotyledons, hypocotyls, leaf, ovary, protoplast, petiole root,
anthers, etc. Haploid generation through anther/pollen culture is recognized as
another important area in crop improvement. It is useful in being rapid
and economically feasible.
Plant breeders are continually searching for new genetic variability that is
potentially useful in cultivar improvement. A portion of plants regenerated
by tissue culture often exhibits phenotypic variation atypical of the
original phenotype. Such variation, termed somaclonal variation may be heritable i.e. genetically stable and
passed on to the next generation. Alternatively, the variation may be
epigenetic and disappear following sexual reproduction. These heritable
variations are potentially useful to plant breeders.
2. Genetic Engineering of Plants
Genetic engineering
technique uses many useful genes have been introduced into plants and many
transgenic plants have been developed in which the foreign DNA has been stably
integrated and resulted in the synthesis of appropriate gene product.
Transgenic plants have covered about 52.6 m hectares in the Industrial
and developing countries up to 2001. Genes for the following traits
have been introduced to the crop plants.
a) Herbicide Tolerance
Transgenic plants are
developed that are resistant to herbicides allowing farmers to spray crops so
as to kill only weeds but not their crops. Many herbicide tolerant plants
have been developed in tomato, tobacco, potato, soybean, cotton, corn, oilseed
rape, petunia, etc.
Glyphosate is one of the most potent broad spectrum
environment friendly herbicide known. Glyphosate kills plants by blocking
the action of an enzyme (5-enolpyruvyl shikimate-3-phosphate synthase) (EPSPS)
an essential enzyme in the biosynthesis of aromatic amino acids, tyrosine,
phenylalanine and tryptophan. Transgenic plants resistant to Glyphosate
have been developed by transferring gene of EPSPS that over produce this
enzyme thus inhibiting the effect of Glyphosate.
b) Pathogen Resistance
Viruses are the major
pests of crop plants which cause considerable yield losses. Many
strategies have been applied to control virus infection using coat protein and
satellite RNA.
Use of viral coat protein as a transgene for producing
virus resistant plants is one of the most spectacular successes achieved in
plant biotechnology. Coat protein gene from tobacco mosaic
virus (TMV) classified as a positive strand RNA virus has been transferred
to tobacco, making it nearly resistant against TMV.
During the last decade many resistance genes whose products are involved in
recognizing the invading pathogens have been identified and cloned. A
number of signalling pathways which follow the pathogen infection have been
dissected.
A chitinase gene (anti-fungal) from bean plants in tobacco and Brassica
napus showed enhanced resistance to Rhizoctonia solani.
c) Stress Resistance
A number of genes
responsible for providing resistance against stresses such as to water stress
heat, cold, salt, heavy metals and phytohormones have been identified.
Resistance against chilling was introduced into tobacco plants by introducing
gene for glycerol-1-phosphate acyl-transferase enzyme from Arabidopsis.
Many plants respond to drought stress by synthesizing a group of sugar
derivatives called polyols (Mannitol, Sorbitol and Sion). Plants that
have more polyols are more resistant to stress.
d) Fruit Quality
Tomatoes which ripen
slowly are helpful in transportation process. Transgenic tomato with
reduced pectin methyl esterase activity and increased level of soluble solids
and higher pH increases processing quality.
Tomatoes exhibiting delayed
ripening have been produced either by using antisense RNA
against enzymes involved in ethylene production or by using gene for
deaminase which degraded l-aminocyclopropane-l-carboxylic acid (ACC) an
immediate precursor of ethylene. This increases the shelf life of
tomatoes. These tomatoes can also stay on the plant long giving more time for
accumulation of sugars and acids for improving flavour.
e) Pest Resistance
The insecticidal beta
endotoxin gene (bt gene) has been isolated from Bacillus thuringiensis the
commonly occurring soil bacteria and transferred to number of plants like
cotton, tobacco, tomato, soybean, potato, etc. to make them resistant to attack
by insects. These genes produce insecticidal crystal proteins which
affect a range of Lepidopteran, Coleopteran, Dipteran insects. These
crystals upon ingestion by the insect larva are solubilised in the highly
alkaline midgut into individual protoxin.
Male
Sterility and Fertility Restoration: This is helpful in
hybrid seed production. Transgenic plants with male sterility and
fertility restoration genes have become available in Brassica napus.
It facilitates production of hybrid seed without manual emasculation and
controlled pollination as often done in maize.
3. Molecular Markers
The possibilities of
using gene tags of molecular makers for selecting agronomic traits have made the
job of breeder easier. It has been possible to score the plants for
different traits or disease resistance at the seedling stage itself. The
use of RFLP (Restriction Fragment Length polymorphism), RAPD (Random Amplified
Polymorphic DNA), AFLP (Amplified Fragment Length Polymorphism) and isozyme
markers in plant breeding are numerous.
RFLPs are advantageous over
morphological and isozyme markers primarily because their number is limited
only by genome size and they are not environmentally or developmentally
influenced. Molecular maps now exist for a number of crop plants
including corn, tomato, potato, rice, lettuce, wheat, Brassica species and
barley.
4. Genetic Modification of Microbes
By using DNA recombination technique it has been possible to
genetically manipulate different strains of these bacteria suitable to
different environmental conditions and to develop strains with traits with
capacity for better competitiveness and nodulation.
a) Biopesticides
Biopesticides are
biological organisms which can be formulated as that of the pesticides for the
control of pests. Biopesticides are gaining importance in agriculture,
horticulture and in public health programs for the control of pests.
The advantages of using biopesticides are many. They are specific to
target pests and do not harm the non-target organisms such as bees, butterflies
and are safe to humans and live stocks, they do not disturb the food-chain nor
leave behind toxic residues.
Some of the microbial
pesticides used to control insect pests are Bacillus thuringiensis species
to control various insect pests. Insecticidal property of these bacteria
is due to crystals of insecticidal proteins produced during sporulation.
These proteins are stomach poisons and are highly insect specific. Bt
toxins could kill plant parasitic nematode too.
b) Biocontrol Agents
These are other microbes
which are antagonistic to several pathogenic fungus and are good substitutes to
fungicides or insecticide. These are Bacillus sp. Pseudomonas
fluorescens, Trichoderma, Verticillium sp., Streptromyces spp. etc. These organisms are
commercially available.
The extent of commercial
application of plant biotechnology is the important mark for measuring the
vitality of this newly emerging technology. Small and marginal farmers
can adopt less expensive technologies like the use of biofertilizers and
biopesticides while capital intensive technologies can be adopted
by rich farmers.
Horticulture Biotechnology in Pakistan
Agriculture sector is
the mainstay of Pakistan`s economy. However, the sector is not contributing to
the economy in line with its real potential. All major crops in the country
have low productivity because of inputs mismanagement. Application of
biotechnology on agriculture sector and genetically modified crops can increase
the agriculture outputs manifold.
Food Security
The application of
biotechnology by Pakistani farmers would not only result in enhancing
productivity but would also help in addressing food security challenges faced
by the country. Research estimates show that the United States earned over $44
billion worth of revenues by utilising this technology which not only enhanced
the crop yields but also saved them from damage caused by worms.
Bt Cotton
The Bt cotton seeds are
being sown in around 60 to 70% of the area. The benefits of the Bt (Bacillus thuringiensis) food crops,
developed from the biotechnology, are the reduced environmental impact from
pesticides; reduced human pesticide poisonings; increased yields; decreased
crop losses; lower cost of production; and reduced pesticide residues on food.
Increased Crop Production
Biotechnology can help substantially increase the
crops production. Global food shortage, due to both unprecedented increases in
demand and supply deficiencies, has equally opened up an opportunity for
agro-based economies.
Lack of modern technology and mechanization are prime
culprits of low crop yields in Pakistan. Agriculture produce may be bartered
with technology of collaborating countries. These exchanges will build
agriculture sector of the country on sustainable basis and contribute in global
food safety.
Challenges to use Biotechnology
A number of technical, economic, regulatory and
market factors have combined to create hurdles for the utilization of
biotechnology in horticultural crops.
1. Species Diversity
Hundreds of species and thousands of cultivars are
represented among fruit, vegetable and ornamental crops. Thus, introducing a
trait into a specific crop and cultivar may require considerable research and
development before it is even feasible.
The diversity of propagation and
marketing mechanisms also presents challenges, as many horticultural crops are
vegetatively propagated from cuttings or grafting, rather than by seed, and are
perennial, bringing different issues for containment and post-commercialization
stewardship.
2. Multiple Niche Markets
Horticultural markets are highly segmented into a
multitude of niches by location, season, consumer preferences, and other
factors. Satisfying these diverse markets requires many cultivars within each
species that may vary for resistance to pests and diseases, dates of maturity,
seasonal adaptation, colour, shape, taste and other attributes.
3. Requirements of Processors
Some biotech traits would be highly beneficial for
processors, such as high viscosity in tomato or insect resistance in sweet
corn. However, processors often have recognizable brand names that are much
more valuable than any single product. There is little incentive for them to
jeopardize their overall market position by risking protests from anti-biotech
activists over the introduction of a single biotech product. In addition, many
processed products are marketed internationally, so that regulatory approval
would be required in each importing country, possibly with each having
different testing or labelling requirements.
4. Regulatory Requirements
Regulation and monitoring are needed to ensure that
novel traits are assessed for food and environmental safety prior to
commercialization. However, such careful precautions should not be so
restrictive as to present insurmountable barriers to the commercialization of
horticultural products that could provide significant benefits to producers and
consumers as well as to the environment. As noted above, the diversity of
regulations and regulatory bodies is particularly burdensome for commodities
traded internationally, as most horticultural products are.
Future Prospects
Even as the adoption of biotech field crops
increases every year, biotech horticultural products are struggling to emerge
into the marketplace. There is no shortage of targets and applications,
particularly with respect to pest management, where biotech crops could
dramatically reduce the high rates of pesticide use in horticulture.
However, it appears unlikely that additional
biotech traits providing primarily grower benefits (so-called input traits)
will be marketed in the near future for most horticultural crops
(herbicide-tolerant turf grasses may be an exception).
Nutritionally Enriched Foods for Health
Nutritionally improved horticultural products could
appeal to consumers and create demand that would lessen distributor risks.
Nutritionally enhanced “foods for health,” such as canola and soybean oils with
enhanced content of omega-3 fatty acids, are being developed, and if accepted
by consumers, could open the door for acceptance of similar products in
horticultural commodities.
However, most targets for nutritional improvement
require metabolic engineering of multiple genes, which will need additional
research to achieve.
Genomics Advances
Counterbalancing this grim picture for
horticultural biotechnology are some positive developments. Fundamental
scientific advances continue to occur at a rapid pace, and the genomes of
horticultural crops are beginning to be sequenced. Researchers and breeders in
horticultural crops will increasingly be able to access and apply the
information being developed in the more intensively studied model plants like Arabidopsis,
rice and maize.
Regulatory and Biosafety Protocols
The continuing adoption of biotech field crops is
stimulating the establishment of regulatory and biosafety protocols around the
world, and the European Union is slowly beginning to relax its moratorium on
approvals of biotech crops. Thus, while the timeline for a significant impact
of biotechnology on horticulture will be pushed back from earlier predictions,
continued research is creating products that will eventually lead to acceptance
by growers, processors, distributors and consumers.
