Development of a novel set of microsatellite markers and genetic characterization of Italian natural Tamarix populations
Author(s)
Terzoli, Serena
Date Issued
March 10, 2011
Type
Doctoral Thesis
Abstract
Tamarix plants are characterized by tolerance to extreme environmental conditions and represent an alternative resource for the recovery of marginal areas. However, their taxonomy is troublesome, and few molecular markers are available to enable species identification. Transcriptome sequencing projects offer a potential source for the development of new markers, named EST-SSRs.
Thirteen polymorphic simple sequence repeat (SSRs) markers derived from Expressed Sequence Tags (ESTs) from Tamarix hispida, T. androssowii, T. ramosissima, and T. albiflonum were identified and screened on 24 samples of T. africana to detect polymorphism. The number of alleles per locus ranged from two to eight, with an average of 4.3 alleles per locus, and the mean expected heterozygosity was 0.453. Amplification products of these 13 loci were also generated for T. gallica.
Tamarix plants were collected in seven sites from Italian islands, Central and Southern Italy: Imera, Simeto and Alcantara from Sicily, Crati from Calabria, Basento from Basilicata, Baratz from Sardinia, and Marangone from Lazio. It was performed a blind sampling, thus individuals were collected without any regard for species identity. Indeed, despite during our germplasm collection flowers for species identification were collected; a large set of samples remained unidentified. The number of individuals surveyed for site ranges from 24 to 84, with a total of 316 plants. The identities of 85 plants were determined with Baum’s morphological keys, while all the rest (72% of the total) remained unidentified. An assignment method based on the use of molecular markers with a Bayesian statistical approach allowed the identification of individuals among species. It was found a clear assignment of T. africana individuals. Otherwise, it was not the same for T. gallica and T. canariensis, whose individuals were assembled together in a unique genetically homogeneous group (T. gallica-like), consistent with the hypothesis of introgression between species. Starting from a total of 221 unidentified plants the Bayesian approach assigned 142 individuals to T. africana, 78 to the T. gallica-like group, while 11 individuals (3.49%) were considered admixed and discarded for further analysis. The advantage concerning the use of molecular markers for classification purposes is that they can be used to assess differentiation across a wide range of taxonomic levels and address questions of species status by comparing inter-intra taxa differentiation. Thus, a high assignment power panel could be employed not only in the species studied in the present work, but could represent a new, fast and cheap method for species identification in all the taxa belonging to the genus Tamarix. It is noteworthy that only two loci, T1B8 and Ta1350, were required to achieve assignment to the species.
Three sites resulted monospecific stands of T. africana (Alcantara, Baratz, and Marangone), four stands resulted mixed with T. africana and T. gallica-like group contemporarily present in the same site (Crati, Imera Basento, and Simeto), while no any monospecific composition of T. gallica-like was found. The analyses of genetic structure of these populations pointed out the existence of a unique gene pool in Southern Italy for both T. africana and T. gallica-like, with populations characterized by low variability. On the other hand, T. africana populations from Central Italy and Sardinia resulted more differentiated, despite the Mantel test for isolation by
Terzoli: Development of a novel set of microsatellite markers and genetic characterization of Italian natural Tamarix populations
distance was not significant. It means that probably the genetic variability is affected by environmental factors, but it is not clear yet which features are involved.
At the best of our knowledge the present work is the first one regarding the characterization of genetic resources in Italian tamarisks.
Additional information
Dottorato di ricerca in Ecologia forestale
Subjects
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