Genetic Diversity Analysis among Onion Genotypes through RAPD, SSR and ISSR Markers

Onion (Allium cepa L.) (2n =16) is one of the important bulb producing vegetable crops. The knowledge of genetic diversity in a crop species is fundamental to its improvement. However, morphological traits have many limitations, including low polymorphism, low heritability, late expression, and may be controlled by epistatic and pleiotropic gene effects (Cramer and Havey, 1999). Now a day’s very powerful PCR-based techniques have also emerged which are very fast, reliable and require minimal amount of tissue for investigation. The use of molecular markers for the evaluation of genetic diversity is receiving much attention than morphological characterization. The various marker tools are Randomly Amplified Polymorphic DNA (RAPD), Simple Sequence Repeats (SSR), Inter Simple Sequence Repeats (ISSR) and Sequence Related Amplified Polymorphism (SRAP). They have large number of applications like characterization of gene pool, DNA fingerprinting, phylogenetic analysis, molecular dissection of complex traits, and characterization of genome organization. These DNA markers offer several advantages over traditional phenotypic markers, as they provide data that can be analysed objectively. The knowledge acquired through this investigation may play a pivotal role in the application of molecular markers in onion improvement programs.