Evaluation of genetic diversity in populations of lemon balm (Melissa officinalis L.) in terms of agronomic traits, essential oil and citral concentration

With many applications in treating and relieving of illnesses, lemon balm (Melissa officinalis L.) is considered as a valuable medicinal plant; as a result, sufficient knowledge about its genetic variation and its classification is necessary for selecting suitable genotypes for breeding purposes. Therefore, present study was to investigate genetic diversity and relationships between several traits of 11 populations of lemon balm consisted of nine Iranian plant populations and two foreign plant populations using randomized completely block design with three replications during 2011 and 2012 in research farm of University of Tabriz. Results of analysis of variance showed that genetic diversity for most of the traits was significant. Study of genetic parameters revealed that percentage and yield of essential oil, number of stems per plant, fresh weight of stem and citral concentration had the highest amounts of genetic advance, genetic and phenotypic coefficient of variations. The highest heritability was observed on fresh weight of stems per plant (h2=0.71), essential oil percentage (h2=0.59) and number of stem per plant (h2=0.58). Ardabil population was superior in terms of citral concentration and percentage and yield of essential oil among the populations. Pearson correlation coefficients indicated a positive and significant relationship between essential oil yield with chlorophyll index, leaf length and width and essential oil percentage and also a significant negative correlation with number of nodes. In factor analysis based on principal component analysis method with eigenvalues greater than one, five factors were determined that a total of 87.40% of the total variance was explained by them. Cluster analysis divided the studied populations into three groups. Due to the observed variability in the present study, selection of desirable populations for breeding programs regarding to improvement of agronomic traits and essential oil of the species is possible.