Bulb onion (Allium cepa), which belongs to the family Amaryllidaceae, is one of the oldest vegetative crops known to humans. Despite its high economic value, only a few reports are available on the use of molecular markers in genetic diversity analysis of Allium cepa for its improvement. Molecular genetic markers have been widely used as powerful tools for analyzing the plant genome. In particular, Microsatellites or simple sequence repeats (SSRs) markers are tandem repeats of one to six bp in length and have been proven to be the most powerful polymerase chain reaction (PCR)-based DNA markers in plant diversity analysis. In this study, the genomic DNA was isolated from different Allium cepa lines. The ESTs and gDNA sequences of onion were collected from National Center for Biotechnology information. The SSRs with two to five motifs over a length of 12 bp, were identified using SSRIT (Gramene) software. The PCR products of 100 to 350 bp in length containing SSRs, primers was designed using Primer3 with lengths of 20 to 24 bp and a melting temperature of 60℃. The SSR markers with high polymorphism-information content (PIC) levels was useful for collecting progeny with high genetic homogeneity for onion breeding, and to obtain representative marker sets for genetic tests. The SSR Finder program and the developed SSR markers could be a useful resource for genetic diversity and purity testing in onion.

Onion is one of the most widely consumed vegetables. There are many cultivars, which are grouped according to skin color as yellow, white or red. Onions can also be classified as sweet or non-sweet. Their importance in cooking comes from their typical taste and flavour. The sugars, pyruvic acid accumulation and transcript level of some transcription factors involved in the biosynthesis of high sugars and pyruvic acid was analyzed at different stages of bulb onion (Allium cepa) growing under light and dark condition using High Performance Liquid Chromatography (HPLC) and Quantitative real time PCR. A genetic map and cultivar lines 36101and 36122 were used to identify transcription factors controlling pungency and sugar. We compared 2 different lines for low pungency and high sugars during water and photoperiod stress, which showed significant positive phenotypic and genetic correlations. These results could be presumably used as useful information to obtain onion varieties rich in sugars.