Evaluation of Diversity in Morphological, Agronomical and Essential Oil Content Characteristics of Different Genotypes of Mentha longifolia L. from Iran

Introduction Mentha is one of the most important genera of aromatic plants which belongs to the Lamiaceae family. The genus of Mentha is distributed across Asia, Africa, Australia, Europe, and North America. Mentha longifolia L., also known as wild mint, is a fast-growing aromatic perennial herb. It is widely used as herbal medicine and is beneficial for the immune system and fighting with secondary infections. The essential oil of this plant is partly responsible for the decongestant, antispasmodic and antibiotic effects. Currently, much emphasis is being laid on conserving plant germplasm as valuable bio-resources. Selection between and within accessions for a high level of herbage yield and other characters requires an effective tool to be applied by mint breeders. Achieving to cultivars that are more capable of optimum producing is a breeding goal. The objectives of this study were to analyze the diversion of the agronomical traits of Mentha longifolia L. genotypes from different regions of Iran under a similar condition in order to find the superior genotypes and introduce for the domestication of this plant. Material and MethodThis research was performed at the research field of the Ferdowsi University of Mashhad. The field is located at 36˚15' North latitude and 59˚38' East longitude, at an altitude of 985 meters. The information related to temperature and precipitation was obtained from climate station. Soil sampling was done in the depth of 0.3 meter and physical experiments on samples were done before starting the experiment. The field was fertilized by 25 kg/ha animal manure. Seeds of 20 genotypes of M. longifolia L. were prepared from Gene Bank of Research Institute of Forests and Rangelands and a view of the wild mint genotypes distribution was presented on the map. The experiment was performed in a field with 500m2 areas in 2015-2016 growing seasons. The experiment in form of compound analysis arranged in complete randomized design with three replicates of 20 wildmint's genotypes in every replication. In each furrow, fourteen bush was totally studied, in which the distance between the two plants was 20 cm. The plot was considered 1.2 by 3 m and the distance between rows was 0.50 m. The dimension in the plots for every replication area was 3.6 m2 and the distance between blocks were 1.5 and between experimental units were 0.5 meters. Picking up was done after elimination of 0.5 meters from every side of replication. The essential oil was extracted using Clevenger type apparatus and by hydrodistillation. Results and DiscussionAnalysis of variance showed that the effect of the diversity among the genotypes on morphological, agronomical and essential oil yield parameters of wild mint was significant (P≤0.01). The results of this study showed that Mentha longifolia L. herb has a high diversity under the same culture conditions among genotypes collected from 20 regions of Iran.  Correlation result shows that vegetative organs have more effect on the essential oil content than the reproductive organs. This may be due to the distribution of essential oil accumulation and storage sites, which requires further research in this regard. The study of vegetative and reproductive characteristics suggests that the genotypes of the dry and semi-arid climates have different conditions, which may causes the separation of their genotypes compared with the other genotypes. The bi-plot, based on PC1 and PC2, reflects the relationships between the studied genotypes. The results of bi-plot of cluster analysis confirmed that genotypes were divided into two main groups based on agronomical and morphological traits. Conclusion Finally, plants of genotype G13 belongs to Hormozgan province and then G16 genotype belongs to Khuzestan province were selected because of more biomass, more aerial part volume and also the most essential oil performance compared to the other genotypes. Desirable traits for the aerial part such as the time of flowering, leaf length, leaf width, plant height, the highest number of leaves in the stem and internode distance are important traits that should be considered. In addition, the cultivation of these genotype in order to the further production can be the great help in the domestication of this species and, given the fact that the diversity is a precursor of breeding, this research can be an introduction for future breeding operations. However, further research is needed to confirm the phytochemical superior genotypes.