Genetic diversity (RAPD) in natural Lithuanian populations of common ash (Fraxinus excelsior L.)

Randomly amplified polymorphic DNA (RAPD) analysis was used to examine the genetic diversity and structure of ten natural Lithuanian common ash (Fraxinus excelsior L.) populations. A total of 99 trees were studied using six arbitrarily selected primers. Seventy-six RAPD bands ranging in size from 0.45 to 2.8 kbp were scored for analysis. Differences in the level of DNA polymorphism among the populations were established. The percentage of the polymorphic DNA fragment in the ten populations studied varied from 57.9 to 92.1%. The estimates of Shannon’s phenotypic diversity index ranged from 0.312 for the Pakruojis population to 0.532 for the Silute population, averaging to 0.44. Most of the genetic variations were found among individuals within the populations, while the interpopulation variance component accounted for 8.3% (P = 0.001). The low interpopulation differentiation implies an extensive gene flow among them. Genetic differences among the populations appeared due to the frequency differences of amplified fragments rather than to the absence or presence of particular RAPD bands. Both the principal component analysis and UPGMA cluster analysis of genetic distance values revealed a varying degree of separation among the populations with a considerable overlap among them; however, the clusters did not precisely reflect the geographic position of the populations. A medium-to-strong negative correlation between population genetic diversity characteristics and the longitude and climate continentality index of population locality was found to indicate existence of a clinal trend and a higher genetic diversity in more maritime West Lithuania.