Need to avoid genetic uniformity over a long period is clear from examples of agricultural pathogens viz., corn leaf blight, wheat rust, potato blight. In addition, genetic resources have been used in increasing agricultural production. Yields of many corps increased dramatically between 1930 and 1980.
Production of rice, barley, soybeans, wheat, cotton and sugarcane has doubled, that of tomato has tripled and of corn, potato and sorghum has quadrupled. Plant breeders use of genetic diversity accounts for at least one half of that doubling. Maintaining agricultural productivity requires constant input of new genetic material to overcome crop losses due to pests.
Resistance to at least 32 major tomato diseases has been discovered in wild relatives of cultivated tomato. Genes for promoting resistance to 16 of these have been bred, allowing tomato production in areas where they could not otherwise have grown.
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Insect resistance, tolerance to temperature extremes, salinity tolerance, drought tolerance and tolerance of water logging are among the traits expressed in wild relatives that may be useful in breeding commercial tomatoes.
Techniques and Background for Conservations of Genetic Resources:
There are two major alternatives for conservation of genetic resources: in situ and ex situ. In situ conservation refers to conservation of genetic resources in wild population and land races and it is often associated with traditional subsistence agriculture.
If focus is only on agricultural varieties, the approach is only partially effective because traditional crop varieties, though much more diverse than elite varieties, are themselves much less diverse than wild population and wild relatives.
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An attractive approach is to combine nature reserves focused on protection of wild races and wild relatives with traditional agricultural practices. Ex situ conservation of genetic resources off-site in gene bank, often in long term storage as seed. Seeds of many important tropical species are recalcitrant, i.e., difficult or impossible to store for long periods. Many crop plants are clonally propagated.
Background for Conservation:
Landscapes to Gene:
Half of world’s mangrove forests are destroyed either by coastal development or pond construction for growing shrimps (Chui, 1999). Many mangrove forests are quickly disappearing mainly for uncontrolled and explosive growth of industrial shrimp aquaculture. Mangrove areas have declined from 450,000 ha in 1920 to 132.500 in 1990 in Philippines.
Half of the mangrove lost in 1952-1987 was converted into brackish water fish and shrimp ponds (Primavera, 1995b) which resulted in habitat loss of wild juvenile shrimps, ecosystem health deterioration and alteration of way of life long held in coastal communities. About 20 years ago, industries began to realize the ocean potential for farming purposes.
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“Blue” revolution started making oceans an area for harvesting and gradually expanded involving developing nations around world. Unregulated growth of coastal shrimp aquaculture industry has been stimulated by financial institutions as a way to thrive in global market. Shrimp aquaculture has raised rapidly, provided jobs for people and accounts for roughly one-fourth of shrimp sales.
Genetic concern that needs to be addressed is indiscriminate use of chemicals in aquaculture facilities. Mortalities and morphological deformities in shrimp larvae due to widespread use of chemicals like oxytetracycline, nitrofurans and chloramphenicol are reported (Primavera, 1993b). Pathogenic bacteria causing luminous vibriosis in shrimp area are resistant to antibiotics (Baticados ei al., 1990b).
Prevalence of infectious diseases in shrimp larvae suggests drug resistance in pathogens, following rampant use of antibiotics in Philippines hatcheries in 1980s (Baticados and Paclibare. 1992).
Evolution of antibiotic resistance in bacteria is known to be genetically determined (vide Brown, 1989). Indiscriminate use of chemicals and therapeutics in shrimp industry has probably weakened shrimp’s immune system and consequently its ability to respond to a pathogenic attack.
Heavy Metals, PCBs and PAHs:
Aquaculture intensification has made use of chemicals and biological products inevitable. Use of chemicals has intensified particularly in marine shrimp cultures. In most countries, these products are readily available in local markets as disinfectants, antimicrobials, soil and water conditioners, plankton growth promoters, organic matter decomposers, feed supplements and pesticides.
Chemotherapy is commonly used to treat fish disease. But in Philippines, this is widely practiced in shrimp culture. Polychlorinated biphenyls are manufactured by rapid chlorination of biphenyl, commonly used in electric insulators, rubber and paper industries as plasticizers.
These are stable pollutants and stored in adipose tissues with high toxic effects on immune system. They atrophy lymphoid tissue and suppress immunity. Immune-suppressants are found in following chemicals:
i. Heavy metals’, lead, cadmium, nickel, chromium, methyl mercury and arsenic.
ii. Pesticides: DDT, dieldrin, methyl parathion, chlordane, hexachlorobenzene
iii. Halogenated hydrocarbons: PCB, polybrominated biphenyls, TCDD, trichloroethylene, chloroform.
PAHs are benzo[a]pyrene, methycholathrene, benzene. Immunostimulants are found in metals as nickel, beryllium and platinum. These substances induce a variety of clinical manifestations and cause allergies.
Polycyclic aromatic hydrocarbons are carcinogen. Sources found in marine and freshwater include spillage and seepage of fossil fuels, discharge of domestic and industrial wastes, atmospheric deposition and runoff.
There is a direct relationship between PAH concentration in river water and degree of industrialization and human activity in surrounding watersheds. Rivers flowing through heavily industrialized areas may contain 1 to 5 ppb total PAH, compared to unpolluted river water, ground water or seawater that usually contains less than 0.1 ppb PAH. PAHs bioaccumulation in aquatic organisms from water, sediments and food.
Shrimp aquaculture and genetic diversity:
Danger posed by shrimp aquaculture to genetic diversity of wild stocks is through accidental or intentional release of potentially inbred shrimp from culture systems (Goldberg. 1996). Selection practices (e.g., for size, colour and growth) in shrimp hatcheries tend to decrease genetic diversity of cultured stocks.
If large number of cultured or genetically modified shrimp escape or are released, their interbreeding with wild P. mondon may establish hybrid populations that could displace native shrimp or otherwise significantly alter natural ecosystem in undesirable ways (Goldberg, 1996).
As indicated by Altukhov and Salmenkov (1990), even so-called successful acclimatization frequently have unfavourable ecological consequences for native populations, because natives are forced out through competition for food and spawning sties or affected by spread of infections and lethal disease to which they are not immune.
Introduction of exotic species and gene pool, alternation by interbreeding of cultured and wild stocks has been considered as biological pollution that is potentially irreversible with ecosystem -wide repercussion (Weston, 1991).
Exotic species have been introduced to Philippines (Primavera, 1993a) and a significant reduction of genetic diversity has found in cultured shrimp populations. Genetic differentiation patterns in wild shrimps are positively associated with mangrove status and shrimp culture systems in surrounding area near collecting sites.
That both mangrove loss and intensification of shrimp culture systems influence genetic compositions of wild penaeids population is suggested. In short term, massive conversion of mangrove forests into shrimp ponds may increase shrimp production. In long run, fitness of wild populations will suffer from loss of genetic diversity and increase susceptibility to disease.
Genetically modified shrimp-(GMS):
Since its evolution from selective breeding of animals and plants, transgenic is being used more and more. Some promote the advancement of genetically modified organisms and others completely against it. Overall intention of transgenic is to improve and refine overall genetic structure of animals and plants.
The latest genetic modification have been in fish aquaculture, where salmon have been modified to grow faster and bigger. This increase in fish production or in case of any increase in animals that are consumed by humans as dietary staples may have some benefits.
However, in the United States, the FDA has not approved any genetically modified animals or plant product to be consumed by humans (http://www.fda.gov/cvm/index/consumer/ transgen.html’ 2001).
Possible benefits of transgenic science are that it can help feed developing or third world nations. Modified animal’s product can be made to carry vaccines, which can help immune system by increasing disease resistance. But there are many downfalls to genetically modified animals. GMOS are contradiction of Mother Nature.
By transforming animals genetically, we are messing the nature made balance. One slight alteration could affect entire environment. A GMO that is placed in environment will tip over ecological balance.
This can happen by creating competition between modified and wild population, tainting gene pools by mixing wild population with GMOs and effects on natural species diversification after introduction of GMOs.
It is a mystery that may contain too many dangers. Public are concerned with the right the animals lose, once they are modified. Treatment of these animals may be unjust, since outcomes cannot always be understood till after the study, the animals may be very uncomfortable. Ethically, it bothers many people for the above stated reasons.
Effects on public safety and health are also not fully researched. Economically, this may cause problems for farmers who may have to pay higher prices to use these genetically modified animals.