Genetic relationships and structured diversity of Lactuca georgica germplasm from Armenia and the Russian Federation among other members of Lactuca L., subsection Lactuca L., assessed by TRAP markers

Abstract

We studied the genetic relationships of Lactuca georgica samples originating in Armenia and the Russian Federation with samples representing four other predominantly self-pollinating wild Lactuca species (L. serriola, L. aculeata, L. saligna, and L. virosa) originating in various countries, as well as with samples representing cultivated lettuce, L. sativa by using 48 TRAP markers. We also visualized their genetic diversity and structure. The present study is likely the first molecular phylogenetic evaluation of a detailed screening of L. georgica germplasm. Data analysis of the three major wild species in this study, L. georgica (134 samples), L. virosa (57 samples), and L. serriola (40 samples) showed that allele frequencies of all 47 polymorphic loci varied significantly among the species. A total of 11, 9, and 10 alleles were unique to L. georgica, L. serriola, and L. virosa, respectively; 71% of TRAP marker diversity was between species. The Neighbor-Joining tree clearly clustered the whole set of 238 samples according to their taxonomic determination. It also reflects the gene diversity as well as the genetic distance values among samples representing the between and within variance of the various species. The L. georgica samples clustered most distantly from the L. sativa samples. The interspecies comparisons between samples belonging to L. georgica with those belonging to L. sativa displayed a high distance, lower only from the interspecies comparisons between samples belonging to L. virosa (in the tertiary gene pool of cultivated lettuce) with those belonging to L. sativa. Thus, additional molecular data with more hybridization experiments are necessary to reconsider if L. georgica is indeed a constituent of the primary gene pool of cultivated lettuce. The L. georgica samples were divided into two sub-clusters, with samples collected in southeast and central Armenia grouping together while all those collected in the north and Dagestan grouped together.