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Genetic Improvement: Molecular-Based Strategies

Soybean (Glycine max (L.) Merr.) is the world’s primary source of protein feed supplement for livestock and accounts for much of the world’s vegetable oil supply. Additionally, healthy aspects of soyfoods go beyond the oil and protein and include minor compounds with nutraceutical properties such as isoflavones, saponins and tocopherols (Rajcan et al., 2005). Over the past three decades, world production of soybean has tripled, from 75 449 966 t in 1978 to 230 952 636 t in 2008 (www.fao.org), what is attributed to the scientific and technological developments in most regions as well as increasing world population, consumer acceptance and consumption of soybean in non-traditional regions of the world. All the sectors, involved with the entire soybean production and processing chain, have responded accordingly to comply with the demands of a globalize economy. The genetic improvement of soybean, based on breeding strategies, contributes to advances in production and food processing industry by developing high-yielding and high-quality soybean cultivars, hereby enhancing value-added, healthy and safe properties of final soy products. Yield has been and remains the trait of greatest emphasis by breeders, as it is the trait with the greatest effect on a producer’s net income. Studies of genetic progress reported that yields increased about 15 to 38 kg ha-1 annually over the period of seventy years (Specht et al., 1999 ; Wilcox, 2001 ; Ustun et al., 2001 ; Egli, 2008). Besides yield, progress has also been made in selecting for resistance to pathogens, insects and nematodes, tolerance to other production hazards, improvement in seed protein and oil, as well as other agronomic characteristics. The genetic improvements have been accomplished mainly through the use of conventional (also termed empirical or traditional) breeding. The conventional breeding strategies are based on crossing, selection and fixation of superior phenotypes to develop improved cultivars and breeds suited to specific conditions with the aim to fulfill the needs of farmers and consumers. As the result of soybean self-pollinating reproductive behavior, conventional breeding procedures such as pedigree breeding, single pod descent, backcrossing and bulk population breeding are some of the more common procedures used to develop soybean cultivars. Although progress in soybean breeding accomplished only by Soybean - Molecular Aspects of Breeding 58 conventional breeding methods is significant, for further genetic advances in soybean germplasm the use of conventional breeding methods exclusively is no longer sufficient. There are multiple reasons for that. First of all, the development of new cultivar with conventional breeding methods requires at least ten generations. The length of this process is often in disproportion with rapid changes in market demands. In fact, on global level, changes in climate, soil structure and fertility, production technology, appearance of new phytopathogen races etc. became so rapid that the cultivar developed by conventional hybridization of parents with desired traits about ten years ago is no longer capable of accomplishing its genetic potential due to environmental stress factors. In addition, the burden of undesired genetic material (material incompatible with set breeding aims) constitutes a big problem in conventional breeding, because the elimination of undesired phenotypes requires more area, more time and thus bigger investments. In classical genetic improvement programs, selection is carried out based on observable phenotypes of the candidates for selection and/or their relatives but without knowing which genes are actually being selected. Plant scientists have made significant advances in understanding the agronomical, species-specific, breeding, biochemical and molecular processes that underlie important genetic, physiological and developmental traits, or that affect the ability of plants to cope with unfavorable environmental conditions for several decades (Gepts, 2002). The discoveries and implementations of biotechnology and molecular biology for selection purposes provide a stable background for generating of new knowledge and practical use in agricultural research and practice as well as to meet the growing demand for more and with better quality food and feed (Todorovska et al., 2010). Main objectives of plant biotechnology are attempts to engineer metabolic pathways for the production of tailor-made plant polymer or low molecular weight compounds and the production of novel polypeptides for pharmaceutical or technical use. In general, goals of plant biotechnology are not much different from classical breeding goals. They can be divided into attempts to optimize input and output traits. Input traits refer to increased resistance towards abiotic and biotic stress, strategies to increase crop yield and to improve post-harvest characteristics. Attempts to improve output traits include production of foreign proteins for pharmaceutical and technical use, production of endogenous or novel polymers for food and non-food applications as well as synthesis of low molecular weight compounds including vitamins, essential aminoacids and pharmaceutically relevant secondary plant products (Sonnewald & Herbers, 2001). Scientists in the laboratory can genetically engineer soybean plants with unique genes, but plant breeding is necessary to put the new transgenes via sexual reproduction into the proper genetic background so that it is adapted to the intended areas of use. Recent developments in molecular biology and genomics are greatly accelerating the speed with which knowledge gained in basic plant science can be applied to species improvement (Dekkers & Hospital, 2002). Therefore, the molecular based plant breeding techniques are assuming an increasingly more important role in genetic improvement of soybean germplasm. Currently, conventional breeding strategies have priority, and in combination with molecular technologies have provided the possibility of broadening genetic variability of cultivated soybean as well as development of new germplasm that is better adapted to new market, production and environment demands (Verma & Shoemaker, 1996 ; Orf et al., 2004 ; Sudarić et al., 2008, 2010 ; Vratarić & Sudarić, 2008 ; Mladenović Drinić et al., 2008 ; Cober et al., 2009). Modern biotechnology application in soybean breeding can be divided in two major categories: Genetic Improvement: Molecular-Based Strategies 59 - molecular genetics and, - genetic transformation. Molecular genetics studies how genetic information is encoded within the DNA and how biochemical processes of the cell translate the genetic information into the phenotype. Genetic transformation involves the alteration of the genetic constitution of cells or individuals by directed and selective modification, insertation of native or foreign gene, or deletion of an individual gene or genes. According to Shoemaker et al. (2004), soybean has emerged as a model crop system because of its densely saturated genetic map, a welldeveloped genetic transformation system and the growing number of genetic tools applicable to this biological system. The emphasis in this chapter will be on selected information about new technological developments derived from molecular biology for soybean breeding purposes. Two main aspects will be considered: the use of genetic markers and transformation (genetic modification).

soybean, genetic marker, genetic transformation

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