International Journal of Scientific World, 2 (1) (2014) 16-20 ©Science Publishing Corporation www.sciencepubco.com/index.php/IJSW doi: 10.14419/ijsw.v2i1.1785 Review Paper Molecular marker assisted selection as approach to increase the selection efficiency of drought tolerant genotypes M.R. Shiri *, K. Akhavan Agricultural and Natural Resources Research Center of Ardebil Province, Moghan, Iran *Corresponding author E-mail: mohammadrezashiri52@gmail.com Copyright © 2014 M.R. Shiri, K. Akhavan. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Identifying the complete-linked molecular markers with target gene and mapping its chromosome locus is an important goal in plant breeding for gene cloning and marker-aided selection. Due to complexity of the interactions, in most of the agronomic traits, especially the interaction between the grain yield and the environmental factors, classic methods do not function appropriately in improving agronomic traits at present. If the selection is made based on genotype by DNA markers, the efficiency of selection will increase considerably. In a genetic evaluation program, the combination between the data from the linkage between marker position and quantitative traits loci (QTL) as well as the phenotypic data can be used to increase the accuracy of the assessments and thereby the accuracy of selection. The selection in which inherited values are used along with the marker data in selection of superior genotypes in a breeding program is called Marker-assisted-selection (MAS). Keywords: MAS, QTL, Water Stress, Maize. 1. Introduction Conventional plant breeding is dependent on appropriate environmental conditions in which to identify and select desirable plants. Typically, breeders improve crops by crossing plants with desired traits, such as high yield or drought tolerance, and selecting the best offspring over multiple generations of testing. A new variety could take 8 to 10 years to develop. Breeders are very interested in new technologies to speed up this process or make it more efficient. Since the mid-1990’s, the term 'marker-assisted selection' has entered the plant breeders and genetics science [28]. The MAS term largely refers to all the form of the selections based on genetic data. There are so many drawbacks in the classic selection method in which phenotypic measures are used as follows [18]: a) Environmental factors reduce the accuracy of the selection for important commercial traits. b) It is difficult to measure several traits. c) In classical breeding programs, measurements are performed in a broad sense. It is both costly and time consuming. Given the above-mentioned drawbacks, selection using genetic markers could increase both efficiency and accuracy of the selection compared with selection based on phenotypic data [32]. If it is not possible to analyze both the traits and the pedigree in a broad sense in breeding programs, genetic markers of the major genes can be used provided that they have significant economic impacts [32]. An appropriate method is the one in which molecular markers data is combined with statistical methods. This increases the accuracy, reduces the generation gap, and ultimately increases the response to selection. The advantage of marker- assisted selection on a trait compared to selection based on the phenotype depends on the heritability. Marker-assisted selection is advantageous for following cases [18]: a) When the heritability of the trait is low b) When the traits that are difficult and costly to measure c) When there is no information on the parents of the present population