| Mint is the most important plant in the genus Mentha (Lamiaceae). All species and natural hybrids of Mentha are essential oil bearing; these essential oils have high economic value and are now widely used in foods, medicines industry and daily chemical field. In this article, we evaluated the leaf characters, biomass, production and composition of essential oil of the mint germplasm resources. The chemical and genetic diversity were also analyzed using chemical (composition of essential oil) and molecular marker (Amplified Fragment Length Polymorphism and chloroplast DNA) respectively.The main results were described as follows:1. Evaluation on foliage traits and essential oil production of mint germplasm resources. The results of leaf traits variation showed that great variation was found in leaf traits except the the trait of leaf length/width ratio. The coefficient of variation of these leaf traits was above35%. The leaf weight of M×gracilis-01was highest (0.15g) in the leaf weight trait. The leaf length/width ratio of M. aquatica-01was highest (2.5) in the leaf length/width ratio trait. The leaf area of M. spicata-06was highest (7.8cm2) in the leaf area trait. The oil gland numbers of M.spicata-02were highest (8475) in the oil gland numbers trait. The results of essential oil content, fresh yield and oil production traits showed that great variation was found in these traits except the the trait of fresh yield, the coefficient of variation of these traits was above50%. The fresh yield of M. spicata-08was highest (1467.4kg/mu) in the fresh yield trait. The oil content and production of M. canadensis-02were highest (0.92%and10.3kg respectively) in the content and production of essential oil trait. Correlation analysis showed that the leaf area had very significant positive correlation with content of essential oil, oil production, leaf length/width ratio and oil gland number. The oil production had significant positive correlation with content of essential oil. According to the comprehensive evaluation of oil production, there were ten mint germplasm resources whose per mu production of essential oil in more than6.0kg were selected. Our results showed that there were plentiful variation in leaf and oil production traits and extremely significant correlation among these characters in mint germplasm resources.2. Study and evaluation on compositions of mint oil. The analysis results of compositions of mint oil showed that in total, twenty-seven main compounds whose contents were above5.0%were identified. The contents of these compounds had difference at different flowering stage, the levels of seven compounds reached the maximum in the initial flowering stage, the levels of sixteen compounds reached the maximum in the full flowering stage, and the levels of four compounds reached the maximum in the later flowering stage. Exogenous abscisic acid (ABA) application caused a decline in oil quality by improving the content of menthofuran and reduceing the content of menthol of mint oil, correlation analysis showed that a dynamic balance among the contents of menthol, menthone, menthofuran and pulegone was found, the relationship was menthol=74.78-1.044×menthone-0.705×menthofuran0.796×pulegone. gene expression analysis showed that ABA application affected the expression of genes in metabolic pathways of mint oil. According to the result of evaluation on essential oil compounds, there were20mint germplasm resources that had the potential to produce high quality oil were selected.3. Analysis on relationship of mint germplasm resources using chloroplast DNA marker. The results showed that two main clusters (cluster I and cluster II) were found by neighbour-joining method. Cluster I included M. spicata-M. suaveolens-M. longifolia-M.×gracilis-M. arvensis-M×piperita, and Cluster II included M. aquatica-M.×piperita-M.×piperita-01, the Cluster I was divided three subgroups:①M. spicata-M. longifolia、②M. spicata-M. suaveolens and③M.arvensis-M.×gracilis, the Cluster II was divided two subgroup:①M. canadensis-M.aquatica and②M.×piperita. Our results reflected the relationship between parent lines and offspring lines.4. Analysis on diversity of chemotype of mint germplasm resources. M. spicata accessions included two chemtypes, one was limonene-carvone type, another was1,8-cineole-piperitenone oxide type. The chemotype of M.arvensis-01belonged to limonene-carvone-piperitenone oxide type. The M. aquatica accessions were divided into four chemotype:①menthone-menthol-pulegone type,②linalool-linalyl acetate type,③limenone-carvone type,④1,8-cineole-globulol type. The M×piperit accessions included two chemotypes, one was high menthone-low menthol type, another was low menthone-high menthol type. The M. longifolia accessions were divided into two chemotype, one was limonene-carvone type, and another was piperitone-isocaryophyllene oxide-piperitenone oxide type. The chemotype of M. suaveolens accessions belonged to piperitenone oxide type. The M. canadensis included two chemotypes:menthol-menthyl acetate type and menthone-menthol type. The chemotype of M×gracilis and M. pulegium L. belonged to limonene-carvone type and menthone-pulegone-menthofuran type respectively. The results showed that there were rich chemotypes among these mint germplasm resources that we collected.Correlation analysis between chemotype and chloroplast DNA marker. There was a consistent relationship between chemotype and chloroplast DNA marker, which hinted that there was a certain correlation between chemotype and parent lines.6. Analysis on genetic diversity of mint germplasm resources using amplified fragment length polymorphism (AFLP). The similarity coefficient was between0.44and0.91among the mint germplasm resources, and the average similarity coefficient was0.66. The28mint germplasm resources were could be divided into seven groups:①M. spicata-M. suaveolens,②M×piperit,③M. aquatica-M×gracilis,④M.spicata-M. longifolia,⑤M. aquatica,⑥M. canadensis-M.arvensis and⑦M. spicata-M. longifolia. Our results showed that there was rich genomic diversity among these mint germplasm resources. |
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