Abstract
Onion (2n = 2x = 16) has been a nutritional, medicinal and economically valuable vegetable crop all over the world since ancient times. To accelerate the molecular breeding in onion, genetic linkage maps are prerequisite. However, construction of genetic linkage maps of onion remains relatively rudimentary due to a large genome (about 16.3 Gbp) as well as biennial life cycle, cross-pollinated nature, and high inbreeding depression. In this study, we constructed single nucleotide polymorphism (SNP)-based genetic linkage map of onion in an F2 segregating population derived from a cross between the doubled haploid line ‘16P118’ and inbred line ‘Sweet Green’ through genotyping by sequencing (GBS). A total of 207.3 Gbp of raw sequences were generated using an Illumina HiSeq X system, and 24,341 SNPs were identified with the criteria based on three minimum depths, lower than 30% missing rate, and more than 5% minor allele frequency. As a result, an onion genetic linkage map consisting of 216 GBS-based SNPs were constructed comprising eight linkage groups spanning a genetic length of 827.0 cM. Furthermore, we identified the quantitative trait loci (QTLs) for the sucrose, glucose, fructose, and total sugar content across the onion genome. We identified a total of four QTLs associated with sucrose (qSC4.1), glucose (qGC5.1), fructose (qFC5.1), and total sugar content (qTSC5.1) explaining the phenotypic variation (R2%) ranging from 6.07–11.47%. This map and QTL information will contribute to develop the molecular markers to breed the cultivars with high sugar content in onion.
Highlights
Onion (Allium cepa L.; 2n = 2x = 16) is one of the most widely cultivated and economically and nutritionally important vegetable crops worldwide
The concentrations of the four types of sugar content, including sucrose, glucose, fructose, and total sugar, in onion bulks of the F2 segregating population are presented in Table 1 and Figure 1
The correlation analysis revealed that the total sugar content was positively correlated with each sugar, for instance glucose (r = 0.97), fructose (r = 0.93), and sucrose (r = 0.65)
Summary
Onion (Allium cepa L.; 2n = 2x = 16) is one of the most widely cultivated and economically and nutritionally important vegetable crops worldwide. The quality of fruits and vegetables is largely attributed to the sweetness determined by the level of soluble sugar content. In both vegetables and fruits, sweetness results from sugars such as sucrose, glucose and fructose [4], with fructose being the sweetest, followed by sucrose and glucose [5]. Sugar content affects the sweetness of vegetables and fruits, and influences the taste and palatability [6]. The onion bulbs contain sucrose, glucose, and fructose as the free sugar components which comprise the majority (65–80%)
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