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.
Biotechnologyis 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.
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