Molecular Markers: Assisted Selection in Soybeans

Abstract

Modern agriculture seeks increasing gains in productivity, due to great demand for food and the reduction of new agricultural frontiers. A major concern relates to fungal diseases and pest damage, and productivity growth necessarily implies reducing losses caused by these organisms. Genetic improvement provides plants with different degrees of resistance, which can be used by farmers, making the most economical and efficient management. The process of obtaining resistant cultivars is usually done by the transfer of resistance alleles from exotic sources, which need further evaluation. This strategy has been used successfully in breeding programs for many years. The evaluation process in plants is an improvement methodology with high cost, complex and subject to environmental variations. Another problem encountered concerns the manipulation of plant pathogens in a place where they occur. As an alternative to overcome the problems mentioned above are used molecular markers. With the development of research in molecular biology, there was the possibility of having one more tool in breeding programs, using DNA as the basic material. The markers can be classified according to the methodology used to identify them: hybridization RFLP (Restriction Fragment Length Polymorphism) or amplification of DNA RAPD (Random Amplified Polymorphic DNA); SCAR (Sequence Characterized Amplified Regions); microsatellites (or SSR Simple Sequence Repeats) and AFLP (Amplified Fragment Length Polymorphism). The markers are based on natural variation in DNA sequence and have Mendelian segregation. The use of molecular markers was initiated in the last century, when Bateson & Punnett (1905) indicated the possibility of linkage between genes controlling characteristics of petal color and shape of pollen grain.The strategy of using molecular markers requires basic knowledge about the genetic nature of the trait studied, classifying it as a qualitative or quantitative (Ferreira & Grattapaglia, 1995), whose difference is based on the magnitude of the effect of replacing one allele by another in a given locus. Molecular markers can be a useful tool to monitor the transfer of alleles of interest. In the early stages of intermediate and improving the process is efficient, but final confirmation is essential in field conditions (Alzate-Marin et al., 2005). This need for phenotypic analysis requires quality in the polls so that the marker may reflect the field conditions. The test is performed with molecular markers using only a small