Tuesday, December 3, 2013

Tree barcodes

Podocarpaceae is the second largest family of conifers and mainly found in the Southern Hemisphere. The group comprises about 198 species of evergreen trees and shrubs that are sometimes cultivated as ornamentals in suitably warm climates.

It isn't well known and as a result their use is very limited but Podocarpaceae contain a variety of bio–active compounds such as antioxidants, nordi–terpenes, podocarpic acid, and tatarol. Some of these compounds are known to be antimicrobial, fungistatic, or bacteriostatic, others are cytotoxic and could be used in cancer treatment. However, any potential medical use needs further more detailed research. Furthermore, species of Podocarpaceae are of conservation concern primarily as a result of small population sizes and limited available habitat. Twenty–seven Podocarpaceae species are included in the International Union for the Conservation of Nature (IUCN) red list under the categories of vulnerable (10 species), endangered (14 species), and critically endangered (three species). Two species are included in the appendices of the Convention on International Trade in Endangered Species (CITES): Podocarpus parlatorei is listed in Appendix I (trade is not allowed) and Podocarpus neriifolius is listed in Appendix III (trade with, some limitations, is allowed). That and a slow rate of growth for most species makes harvest of Podocarpaceae generally unsustainable and would require extensive conservation management efforts.

In addition accurate identification of tropical forest trees, such as Podocarpaceae, is often very difficult. The most easily accessed material is usually sterile. If fertile material is present, it is frequently either inaccessible or detached from the tree making it difficult to convincingly associate the fertile and sterile portions. Although sterile material of Podocarpaceae can usually be identified to genus using phyllotaxis and leaf form, accurate species identification often requires careful microscopic examination of internal and external characteristics. Proper use of the existing identification tools requires training in botanical terminology, skill in microtechnique, and familiarity with Podocarpaceae.

Now a team of US and German researchers build a DNA Barcode library for 145 of the species (73% of the family). They generated matK, rbcL, and nrITS2 sequences. In addition, they created a living Podocarpaceae collection in the Botanic Garden of the Ruhr-Universit├Ąt in Bochum, Germany which promotes the protection of rare and endangered species. There the species will be propagated and passed on to other botanic gardens worldwide.

The discrimination power of matK, rbcL, and nrITS2, individually and in combination was relatively low (56.7%) in this study. The authors also state that this is not unusal and that plant DNA Barcoding studies that heavily sample within taxonomic groups usually report low rates of species discrimination. They suggest that sequences of some unlinked genetic markers may however increase the rate of species discrimination. 

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