Identification of Lettuce (Lactuca sativa L.) Cultivars using Newly Developed EST-SSR Markers

Lettuce (Lactuca sativa L.) is a member of the Asteraceae and one of the most widely cultivated vegetables. Sixty five lettuce cultivars have been registered at the Korea Seed & Variety Service for Plant Variety Protection. Molecular markers have many advantages for cultivar identification due to their independence from environmental influences. We developed novel expressed sequence tag (EST) derived simple sequence repeat (SSR) markers from the NCBI EST database and used them to analyze the genetic relationship of lettuce cultivars distributed in Korea. A total of 1,183 SSR primer pairs were developed from 81,330 lettuce ESTs. Out of the 1,183 primer pairs, a random set of 200 EST-SSR primers was selected for characterization with 52 cultivars. Sixteen primer pairs among 200 EST-SSR primers showed polymorphisms between cultivars and repetitive reproducibility on capillary electrophoresis system. Totally 65 polymorphic amplified fragments were obtained using 16 EST-SSR markers. Two to seven SSR alleles were detected for each locus with an average of 4.0 alleles per locus. Average polymorphism information content was 0.576, ranging from 0.142 to 0.754. Genetic distance of clusters ranged from 0.17 to 0.96 by unweighted pair-group method with arithmetical average based on Jaccard’s distance coefficients. A total of 52 cultivars were discriminated by 16 EST-SSR marker genotypes. EST-SSRs developed will be useful for identifying lettuce cultivars and for future study, such as genetic diversity study of germplasms and genetic mapping and molecular breeding.