Genetic structure and diversity in natural populations of three predominantly self-pollinating wild Lactuca species in Israel

It is important to optimize strategies for collecting wild germplasm from their natural habitats for the successful conservation of plant genetic resources. We studied the population structure of three predominantly self-pollinating wild Lactuca species (Lactuca serriola, L. saligna, and L. aculeata). Seeds for this study were collected from individual plants in northern Israel, along a line transect, and two populations per each Lactuca species. The distance between neighboring plants sampled for seeds varied from 1.5 to 37 m. The transect length at single sites ranged from 47.2 to 151.8 m. The taxonomic status of 67 individual plants was morphologically validated during greenhouse multiplication. Both genetic structure and diversity were analyzed by using 11 EST-SSR loci and 230 AFLP markers. Relatively low genetic diversity values were observed, increasing in the following order: L. aculeata < L. serriola < L. saligna. Network analysis clearly separated samples according to their taxonomic determination; also reflecting the gene diversity as well as the genetic distance values among the three species. Nevertheless, given the predominantly selfing character of these species, populations were not uniform (genetically and morphologically). It seems that overall genetic variation in a population increases at its periphery, due to the presence of plants with "non-indigenous" alleles, which are most likely coming from migration and subsequent interpopulation or interspecific hybridization. Mantel tests generally indicated a positive association between genetic distance and micro-geographical distance of a particular population, primarily due to the "outlier" samples collected at a population's periphery.