Classification And Identification Of Invasive Populations Of Solidago In China And The Cut Flower Solidaster Based On Molecular Marker And Morphological Characteristics

Solidago canadensis L. is a perennial invasive alien plant belonging to Solidago L Composite. It was initially introduced as an ornamental plant to Shanghai and Nanjing. Then it escaped into the wild and has been spreading rapidly in China, becoming one of the detrimental weeds. Because of its serious damage to environment and economic development, it has already received more public attention. However, the doubts address to whether there is only one species S. canadensis and cut flower Solidaster just is S.canadensis. Obviously, the most important work is to determine their taxonomic status using modern molecular tools and find out some morphological characteristics for field identification. This work is beneficial to enucidate mechanism of this alien species invasion, predict the potential invasive region and adopt the scientific management measurements.In order to determine the taxonomic position of invasive populations of Solidago in China and identify the cut flower Solidaster, the internal transcribed spacers (ITS) of103invasive populations including Solidago invasive populations in both China and Japan and native populations in North America were sequenced. Also, we observed11morphological characteristics and used them to established cluster dengegram and classify those populations through R software. The main results are given as follows:1. Classification and identification of invasive populations of Solidago in China and the cut flower Solidaster based on ITS sequencesWe sequenced the internal transcribed spacers (ITS) of103populations of Solidago genus collected from China, Japan and North America respectivley. The ITS sequences odbtained were blasted in NCBI database to find out the target sequence which has the highest homology with the tested sequence. Furthermore, we can determine the species of the tested samples. ITS phylogenetic trees of the tested samples and closely-related species were reconstructed based on our sequence data in combination with other species from GenBank using Maxium Parsimony by means of MEGA4.1software. By this means we could further verify the taxonomic status of the samples.The results showed that all the61invasive populations of Solidago collected from two municipalities and10provinces in Eastern, Central, Southwest and South China and all samples of the cut flower Solidaster were all S. canadensis without discovering S. altissima. Among the61invasive populations,58populations had exactly the same ITS sequence of S.canadensis in GenBank. The other three populations from Changsha, Jiujiang and Shangrao had slightly different ITS sequences from other populations in A absent at position14, A absent at position597and T addition at the beginning, but they still belonged to S. canadensis. Also we found that Solidaster had a higher molecular variation frequency which is consistent with the previous results in our lab. It was also found that S. altissima from Japan and North America, S. canadensis from North America and58populations of S. canadensis from China shared with completely identical ITS sequences which was the same as two ITS sequences of S.canadensis from Genbank with accession numbers are FJ859719(Guangzhou,2009) and EU125361(America,2008). S. altissima and S. canadensis shared exactly the same ITS sequence. The result supports the point of Croat’s view that S. altissima and S. canadensis are the same species and should be merged into one species. Hence, the above conclusion clarifys the doubt about S. altissima existence in China.2. Classification and identification of invasive populations of Solidago in China and the cut flower Solidaster based on morphological characteristicsTo enuncidate the differences in morphological characteristics between the invasive populations of Solidago in China and the cut flower Solidaster and further verify the classification results based on ITS sequnces, we observed11morphological characteristics referring to classification:Length of ray florets (mm), involucral height (mm), number of ray florets, number of disc florets, length and width of leaves, length between triplinerved and leaf base, number of hairs on midrib per2mm length, number of hairs on secondary nerve per2mm length, number of hairs on tertiary nerve per4mm2and number of serrations on leaves. All the data about morphological characteristics were calculated by the method of weighted average, statistically analyzed and clustered by SPSS and MVSP software. Finally, the correlation between11morphological characteristics and the classification of Solidago species were determined by Agricolae and Gplots packages in R software.The results showed that invasive populations from China, Solidaster samples from Nanjing, Lianyungang and Yunnan, S. altissima from North America and Japan, S.canadensis from America were clustered into one group which all belonged to S.canadensis, but seperated from S. gigantea, S. decurrens and S. simplex. This is consistent with the clustering based on ITS sequence and further proved that the invasive populations of Solidago in China and the cut flower Solidaster are all S. canadensis.The correlation between11morphological characteristics and the classification of Solidago species demonstrated that the cut flower Solidaster has more disc florets, shorter ray florets(3.75mm)and involucre(3.09mm), less epidermal hairs on midrib and secondary nerve, less serrations on leaves (8.25), narrower leaves (9.87mm) and shorter length between triplinerved and leaf base (12.63mm), while the invasive populations in China have less disc florets, longer ray florets (4.96mm) and involucre (4.29mm), more epidermal hairs on midrib and secondary nerve, more serrations on leaves (14.70), wider leaves (13.76mm) and longer length between triplinerved and leaf base (19.50mm). Based on these we could distinguish the cut flower Solidaster from the invasive populations in China morphologically. Also we found that S. canadensis had more epidermal hairs on vein, longer involucre (4.00mm) and less disc florets (3.19) but S. gigantea has less epidermal hairs on vein, shorter involucre (3.37) and more disc florets (5.66). According to these results, we could distinguish S. canadensis from S. gigantea morphologically. S. altissima and S. canadensis were similar in morphology without the obvious boundaries.