Patterns of Population Diversity in Lemon balm (Melissa officinalis L.) as Revealed by IRAP Markers

Analysis of genetic diversity and population structure in medicinal plants is essential step in their conservation, utilization and breeding. In the present study, seven primers designed based on long terminal repeats (LTRs) of barley retrotransposons and their combinations were used to amplify DNA fragments from 12 Iranian ecotypes as well as two populations from Germany and Japan based on inter-retrotransposon amplified polymorphism (IRAP) technique. A set of eight most polymorphic primers out of 28 possible single and primer combinations yielded 456 reproducible informative data points, with 95% polymorphism.The mean of Nei’s genetic diversity index and Shannon diversity index were 0.10 and 0.16, respectively. Polymorphism information content (PIC) ranged from 0.22 to 0.32 with an average of 0.27 and marker index (MI) varied in the range of 10.10-29.30 with an average of 14.39. Analysis of molecular variance revealed higher within population molecular variation (76.30%) compared with among populations variation (23.70%). The highest and lowest genetic heterogeneity were observed in Hamedan-2 and Qazvin-1 populations, respectively. The studied genotypes were assigned into five groups based on IRAP data using Neighbor- Joining algorithm and p-distance evolutionary distance coefficient. Populations relationships were resolved using Neighbor-Joining algorithm and Nei’s genetic distance and the populations were grouped into three clusters. Our results suggest that retrotransposon based markers such as IRAP are efficient and reliable markers in determining level of genetic diversity and population structure in lemon balm.