Genetic Relationships of Lactuca spp. Revealed by RAPD, Inter-SSR, AFLP, and PCR-RFLP Analyses

RAPD, Inter-SSR, and AFLP markers were used to assess the genetic diversity of lettuce cultivars and the phylogenetic relationships in Lactuca spp. A total of 216 polymorphic bands from seven RAPD primers, four Inter-SSR primers, and five AFLP primer combinations were used to elucidate the genetic similarity among lettuce cultivars. Forty-four lettuce accessions were subdivided into discrete branches according to plant type: crisphead, butterhead, and stem type, with some exceptions. The leafy- and cos-type accessions were intermingled in other groups with no discrete branch indicating that these are more diverse than others. Three accessions, including the Korean cultivar 'Cheongchima', the Korean local landrace 'Jinjam', and the German cultivar 'Lolla Rossa' were classified as the most diverse accessions. Twenty bands were unique in specific cultivars. Among these, three were specific in a plant type; one in Korean leafy type, one in crisphead type, and one in cos type lettuce. In the phylogenetic analysis among Lactuca species, L. saligna, L. serriola, and L. georgica clustered in a sister branch of the L. sativa complex. Two L. virosa accessions show the highest intra-specific relationships. L. perennis outlied from all the other Lactuca species at a genetic similarity of 0.53 and clustered with two Cichorium species, C. intybus and C. endivia, with genetic similarity of 0.67. The phylogenetic tree was supported by data from polymorphism of chloroplast genome which was revealed by PCR-RFLP.