GM maize ashes for his way

Edição XI | 03 - Mai . 2007

Ernesto Paterniani - epater@merconet.com.net

            Due to its great representativeness as a component of human food diet - present in hundreds of products - as well as animal - foundation for fowl and swine fodder - maize is a culture whose importance do not need comments and introductions.
              However, the great added value of this cereal and its consequent economical relevance in the world agriculture context justify the advances on genetic improvement research in order to guarantee higher quality and yielding indexes while reducing costs and increasing environmental sustainability.
               Here we show maize opportunities and evolutions, from hybrid to transgenic type.

                        

              Wild and domesticated plants
              Agriculture is held as the major invention by humanity  realized some 10,000 years ago in at least two distinctive and independent locations, the Old and New World. Our ancestors had lived for over two million years, competing for survival against stronger, faster, and more aggressive species which put early humans on the verge of extinction in, at least, two occasions. It was the invention of agriculture that granted the survival of the human species, since man initiated the domestication of plants which in turn made them adequate for cultivation.

 

                

                Dr. Ernesto Paterniani  / Dr . Leila Oda - AMBio President


                   The factors involved in the domestication of plants essentially are:
a)   a)  Natural selection for adaptation to new environments and tolerance to pests and diseases.
b) Artificial selection performed by ancient civilizations.
c) Natural intraspecific and interspecific breeding (e.g. wheat and cotton).
                   Parallel to this process some plant species lost their survival capacity in natural environments, if not cropped by man.
              Some examples follow:
·         Absence of natural mechanisms for dispersal of seeds.
·         Loss or reduction of the content of toxic or bitter plant substances.
·         Loss or reduction of protection mechanisms (spines, awns, etc).
·         Loss or reduction of seed dormancy, having faster and more uniform germination.
·         Changes in the color of fruits and seeds.
·         Gigantism and higher productivity.
·         Changes in the flavor and palatability of foods.
·         Higher carbohydrate content in cereals with a concomitant reduction on protein concentration.
·         Changes from perennial life cycle to the annual form.
                    Some changes on the reproduction traits are worth noting:
a)   a)  Changes from allogamy to autogamy (cross pollination to self pollination).
b) Changes from dioic plant from to the monoic form.
 
              The classic or conventional genetic era
             Genetic breeding of plants has evolved into a series of technologies since 1900, the time when Mendelian laws were rediscovered. These technologies, which made possible the improvement on the efficiency of breeding programs, were based on the utilization of reproductive variation among plants:
a)   a) Creation of plants with male sterility, used to facilitate heterosis or hybrid vigor. Plants with male sterility are useful also in the application of recurrent selection in self pollinating species.
b) Self incompatibility and self sterility, employed for the obtention of hybrids in plants of the genus Brassica.
c) Creation of monoploid plants by incomplete fertilization. The occurrence of only the fertilization of the two polar nuclei that will produce the endosperm may result in an haploid embryo from a non-fertilized sphere that will eventually produce an homozygotic plant for the 100% of its genes. It can be considered as a full pure line, extremely useful for genetic studies and to shorten the time needed for the obtention of pure lines from autogamic species derived by the breeding between different varieties.
d) Development of gametophytic genes and super gametophytic, that protect varieties against gene flux.
e) Development of mechanisms for reproductive isolation by natural or artificial selection.
 
               The introduction of new genes in plants
              Considered also as conventional means, artificial mutations included by ionizing or non-ionizing radiation as well as by other physical or chemical agents are common techniques used in the obtention of new varieties. Within the techniques that are independent of sexual reproduction ploidy, initiated around 1920 and mutations are comparatively older than other techniques.
             The genes produced by such treatments are completely random, which is why the  vast majority have deleterial effects and are considered  undesirable. However, within the  thousands of genes created by natural or artificial mutations, several useful genes have been identified which in turn led to the creation of thousands of plant varieties that are officially approved and traded on a global scale.
 
                “At this point it is convenient to stress that both methods for breeding plants, conventional breeding conventional and transgenic, are not and not mutually exclusive complementary”
 
                The time of modern biotechnology
               Biotechnology or the study of processes relative to the nature and structure of the genetic material or DNA led, since 1970, to the development of techniques that enable the transfer of specific genes between species without the need of sexual reproduction. This technology was given the generic name of genetic engineering and the plants obtained through this application, transgenic plants.
             It was only natural that such an impressive technology be used for the creation of new and improved varieties. For the sake of easiness and impact, the first transgenic plants were created with very specific genes, such as those that make varieties tolerant to certain insect pests and herbicides. Examples such as that of soybean tolerant to the glyphosate herbicide and cotton and maize cultivars tolerant to insects are acknowledged worldwide, and are currently grown in all continents. Likewise, transgenic plants with beneficial traits such as superior nutritive value (e.g. higher content of proteins, vitamins, quality fatty acids and mineral supplements) have been created already and others are in an advanced stage of research. The Golden Rice, with yellow kernels due to the presence of carotene vitamin A precursor, holds high hopes to reduce the risk of blindness for millions of children in the Tropics, were rice is the most important component of human diet. As promising as golden rice, the iron-rich rice should help to reduce the levels of iron-deficiency anemia in pregnant women and children.
           At this point it is convenient to stress that both methods for breeding plants, conventional and transgenic, are not mutually exclusive but complementary. As a matter of fact, transgenic traits have been incorporated into varieties bred conventionally, which is proof that plant breeding benefits from the combination of both techniques which have, in turn, shown their efficacy. All new genotypes bred by conventional or transgenic techniques have been dully assessed, being that for transgenic cultivars the evaluations have been especially rigorous, regarding the concern for human health and the environment. The safety of transgenic products, assessed through tests of high scientific standards, has been in practice validated by millions of consumers around the world for the past ten years, without having registered any hazards to human health or the environment. Everything seems to show that transgenic products are as safe as or safer than their conventional counterparts and don't pose threats to the environment.
              The main difference between conventional plant breeding and transgenics lies in that for the former, as well as for other techniques of genetic manipulation, the breeder is responsible for the evaluation and may share this responsibility with other researchers. In transgenics the whole process, from the initial research up to the final stages depends on official approval, usually having a very strong bureaucratic barrier to some specific scientific research. Parallel to this, a host of scientific disciplines involved in the biosecurity evaluation of transgenic products has come to have a major role, which in Brazil deals exclusively with genetic engineering. To emphasize the previous concept, the table on the text elucidates the comparison between mutations and transgenics.
 
                Benefíts from Bt Maize
 
·         Reduction in insecticide use;
·         Reduction in the use of fossil fuels;
·         Reduction in the contamination by mycotoxin producing fungi;
·         Healthier products with less carcinogenic substances;
·         Lower intoxication risks to farmers;
·         Maize with higher value and better quality;
·         Higher profit.

                    

                The coexistence of genetically modified (GM) and conventional maize in crop fields
               Coexistence - The evolution and development of societies led to increased variability and diversity in the different activities, cultures, ideologies, etc. Agriculture was no exception and since its invention, some 10,000 years ago, innovations have been a common trend. History has never recorded the diversity of agricultural activities developed along the 20th century.
              Among those with the highest  impact, heterosis or hybrid vigor, initiated with the appearance of hybrid maize and was later extended to other species. Other significant  genetic alterations included  ploidy, which causes changes in the number of chromosomes, induction of artificial  mutations and the development and utilization of male  sterility in plants. All these  innovations led to the production of thousands of new cultivars, some of which are still in use, serving the different preferences and needs of society. The experience showed that such diversity has not only contributed with benefits to society, but has also coexisted with increasing difficulties.
             GM and conventional maize - Maize is the  species with the highest diversity of races and varieties, which explains its ample distribution from  temperate to tropical climates. Some 300 races have been identified, being the raw material for the thousands of varieties cropped worldwide. Brazil possesses a vast genetic diversity of this species and the indigenous and commercial races have been described. Being maize the emblematic species for allogamic reproduction, the coexistence of all that diversity has been duly preserved. The American indigenous civilizations which had a critical role in the development of countless corn races, knew well how to preserve their cultivars free of undesirable adventitious species.
               Thanks to the recombinant DNA technology new GM maize cultivars are in the market and, as mentioned previously, the same methodologies employed for the prevention of undesirable adventitious species can be useful to the coexistence of both, conventional and transgenic maize. The isolating distance concept has been employed by the indigenous populations as well as present day farmers. The regulations for the production of adventitious-free maize seeds have established a minimum distance of 200 m or a temporal separation of 25 days between planting dates.
             Due to its antiquity and world expansion, there is a vast experience gathered on the different ways to prevent the occurrence of adventitious species in the maize crop, much of it yet to be published but nevertheless known to the average grower. Due to the expansion of hybrid maize, conventional maize growers have been concerned with the preservation of conventional varieties, thus trying to block any breeding between them. The responsibility for the appropriate isolating distance falls then upon the grower interested in maintaining the specific genetic identity. It's the organic farmer who should bare the responsibility for isolation, since it's him who will benefit from the added value of his produce.
             Cultivar Diversity – Agriculture involves the  coexistence of a vast diversity of cultivars from the different species  grown for human and/or animal use. As mentioned  previously, the frequency of breeding between plants is a species related trait and not to the fact of being transgenic. Thus, any gene flux alters the receptor genome, whether the donor is transgenic or not. For autogamous species that self pollinate naturally, the concern for breeding is low, since this is extremely infrequent. Obviously, the concern is mainly focused on allogamous plants such as maize, a species which has numerous hybrids, improved varieties and local land arieties, multiplied by farmers. This scenario requires that for a mature crop to remain free of gene contamination, specific isolating measures be adopted, be them of spatial nature (300 m) or temporal nature (three weeks). These measures are routinely employed by researchers as well as by farmers interested in the preservation of their genetic material.
 
                 “Conclusions
·         The coexistence of different cultivars is as old as Agriculture.
·         Ancient civilizations such as the first American natives, as well as the present day farmers, have learned how to coexist without trouble with cross-pollinating species such as maize.
·         Technology innovations such as hybrid maize have been able to coexist with conventional varieties for a long time.
·         The present state of knowledge shows that for a new technology such as GM maize there are no constraints for its coexistence with other technologies, including organic growing, provided the appropriate measures to avoid the presence of adventitious plants are adopted. This has already been tested in countries that have grown GM and conventional maize in coexistence for many years.
·         It is the farmer's choice to protect the technology he employs, since it's him who'll benefit with extra revenue through this protection.”


Compartilhar

newsletter

Receba nossas melhores
matérias em primeira mão!