Abstract
The objectives of this study were to construct a database of expressed sequence tag (EST)-simple sequence repeat (SSR) markers to identify lettuce cultivars. A set of 370 EST-SSR primer pairs were applied for fingerprinting the lettuce cultivars. Fifty-eight EST-SSR markers showed hy-per-variability and were able to differentiate 92 cultivars. A total of 176 polymorphic amplified fragments were obtained by the 58 markers, and two to eight SSR alleles were detected for each l°Cus with an average of three alleles per locus. Average polymorphism information content (PIC) was 0.425, ranging from 0.022 to 0.743. Cluster analysis was based on Jaccard’s distance coefficients using the method of unweighted pair group. In this method we used arithmetical averages (UPGMA) algorithm categorized 4 major groups, which were in accordance to morphological traits. The eight cultivars of three groups with 100% genetic similarity through SSR analysis were investigated by phenotypic traits. These cultivars including these pairs are very similar in 27 morphological characteristics. Therefore, these EST-SSR markers could be used to select similar cultivars through management of reference collection to complement distinctiveness test of lettuce cultivars.
Highlights
Lettuce (Lactuca sativa L., Asteraceae) is one of the most widely cultivated vegetables [1]
The UPOV suggests that simple sequence repeat (SSR) markers are suitable for a DNA profiling database due to their multi-allelic nature, reproducibility, high polymorphism, easy automation, and co-dominant inheritance [5]
Expressed sequence tags (ESTs)SSRs have advantages over genomic SSRs representing noncoding regions because they are present in coding regions and the expressed sequence data can be retrieved from the public databases [7]
Summary
Lettuce (Lactuca sativa L., Asteraceae) is one of the most widely cultivated vegetables [1]. Sixty-three lettuce cultivars obtained Plant Variety Protection (PVP) at the Korea Seed & Variety Service. This is the fourth highest number among vegetable crops in Korea (http://www.seed.go.kr). A rapid and robust “DNA marker technique” has been used to identify cultivars for the DUS test [2]-[4]. DNA markers have many advantages to identify cultivars due to their independence from environmental influences. There are no reports on applicability for the DUS test using molecular marker in commercial lettuce cultivar. We constructed EST-SSR profiles databases to effectively identify 92 cultivars widely cultivated in Korea and investigated the possibility of utilization in the distinctiveness tests by comparing morphological characterization of lettuce cultivars with limited variability through SSR analysis
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