Marker-Assisted Selection in Crop Improvement
Authors: NANGSOL DOLMA BHUTIA, R.S.LOUSHAMBAM and AIDO TALOH
Molecular breeding is used to describe plant breeding programmes that are supported by the use of DNA based markers. In Plant Breeding, Molecular approaches applied through the use of two main, but entirely different strategies, each of them expediting the process of plant breeding. In the first strategy a variety of transgenic crop have been produced that carry genes, which could not be introduced other by any conventional methods. In the second strategy, molecular markers closely linked to numerous traits of economic importance have been developed in several crops. Marker assisted selection (MAS) is the breeding strategy in which selection for a gene is based on molecular markers closely linked to the gene of interest rather than the gene itself. Here markers are used to monitor the incorporation of the desirable allele from the donor source. Marker assisted selection (MAS) is a combined product of traditional genetics and molecular biology. MAS allows for the selection of genes that controls traits of interest, such traits are colour, disease resistance, etc.
DNA- markers allow the breeder to introduce into their cultivated plant only the gene(s) of interest from a related species through MAS. While conventional breeding methods rely on the transfer of the whole genome (along with the gene of interest, undesirable characters are also co- inherited and have to be eliminated through back crossing followed by selection). DNA- markers allow to eliminate in a few generations ‘undesired’ genome regions. One of the most successful applications of MAS today has been that for introgressing and/or pyramiding major effect genes. Many scientists advance the view that MAS is still in its early phase, in particular for improving quantitative traits. To speed up its implementation, the application gap between research laboratories and plant breeding institutes should be closed. Integrating genomics and bioinformatics into the field of molecular breeding is expected to bring in more fundamentals revolutions in plant breeding.
MAJOR APPLICATIONS OF MAS IN PLANT BREEDING :
Assessment of genetic diversity and parental selection, study of heterosis- maize and sorghum, identification of genomic regions under selection, useful for disease resistance and insect resistance, very effective for introgression of desirable genes from wild into cultivar, being used for transfer of male sterility and photoperiod insensitivity, MAS is very effective and efficient method of transferring resistance to biotic and abiotic stresses in crop plants.
ACHIEVEMENTS OF MAS :
1. Pyramiding of bacterial blight gene Xa5, Xa21, Xa13 by Khush group, IRRI and resistant two rice varieties developed eg. Amgke, Conde in Indonesia.
2. Development of Swarna sub-1. The swarna sub-1 line has been developed by marker assisted backcross breeding, involving Swarna as recurrent parent and FR- 13A as donor parent for submergence tolerance by D. J. Mackill and group at IRRI.
3. Incorporation of Saltol 1 gene in the background IR 64 under progress at IRRI.
4. Marker assisted drought tolerant QTL pyramiding was done in the background of IR64, from two donor STYH and BR24 (Dwivedi et al., 2005).
5. At IARI, Dr. N. K. Singh and group (2003) had combined bacterial blight resistance and Basmati quality characteristics by marker assisted backcross breeding in Pusa Basmati- 1.
6. MAS used in cereals- maize, wheat, barley (CYMMIT, USA, Australia, Canada) for insect- pest resistance, protein quality and other agronomic traits.
7. MAS in India: cultivars Rice (Improve PB-1, Improved Sambha Mahsuri); Pearl- Millet (HHB- 67 and 67-2), Maize (Vivek- QPM9).
CHALLENGES FACED BY MAS :
Improved cost- efficiency, optimization, simplification of methods and future innovation, design of efficient and effective MAS strategies, greater integration between molecular genetics and plant breeding, data management.
FUTURE PROSPECTS OF MAS :
1. Breeders need to acquire knowledge of molecular markers and to implement MAS for all crop.
2. One of the most successful applications of MAS today has been that for introgressing and/or pyramiding major effect genes.
3. Many scientists advance the view that MAS is still in its early phase, in particular for improving quantitative traits.
4. To speed up its implementation, the application gap between research laboratories and plant breeding institutes should be closed.
5. Integrating genomics and bioinformatics into the field of molecular breeding is expected to bring in more fundamental revolutions in plant breeding.
Molecular markers can be effectively utilized for MAS breeding programmes. Though conventional breeding approaches are basic mode of improving crop plants but if assisted with molecular markers can give better results by saving time and labour.
1. Kole, C. and Abbott, A G. (eds). (2008). Genome Mapping. Principles and practices of plant genomics. Vol. 1: Science Publishers, Enfield, NH, USA.
2. Singh, S. P., Sundaram, R. M. and Biradra, S. K. (2006). Identification of simple sequence repeat marker for utilizing wide compatibility gene in inter sub specific hybrid in rice (Oryza sativa L.). Theory of Applied Genetics (113): 509- 517.
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