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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Genetic Structure of Green Ash and the Establishment of Ex Situ Conservation

Location: Floral and Nursery Plants Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
The objective of this study is to apply DNA microsatellite diversity to craft a more efficient sampling strategy for the preservation of genetic diversity of green ash trees in Ohio and surrounding states. In addition, this study will also provide guidelines for the future establishment of a core collection of green ash; i.e., a set of accessions selected to represent a high proportion of the genetic diversity of the overall collection.


1b.Approach (from AD-416):
Microsatellite markers are useful tools for examining breeding systems and patterns of variation within populations, for differentiating among accessions/populations, and for marker-aided selection and gene introgression. In particular, microsatellites can be used to identify individual accessions with a high relative contribution to overall allelic diversity among a set of accession/populations in a germplasm collection. Moreover, microsatellite markers can be used to quantify genetic diversity and its distribution across the landscape, as well as to help define mating structure.

Green ash (Fraxinus pennsylvanica) is one of the most widely planted and adaptable street trees in the Midwest. As with the other species of ash native to eastern North America, it is currently under direct threat from Emerald Ash Borer (EAB). The Cooperators are based in Ohio, and are researching the population genetics of ash trees during the course of the EAB outbreak.

The information to be generated by this study is fundamental for the establishment of a sampling protocol for the ex situ conservation of green ash diversity and its evolutionary potential. More specifically, the knowledge of genetic structure can help direct sampling efforts for specific plant traits, such as host-tree resistance to pathogens and herbivores. It is our objective to use at least ten microsatellite marker loci to determine the levels and distribution of genetic diversity of green ash trees in the four of the five major physiographic regions of Ohio. We proposed to analyze a sub-sample of the seeds of green ash already incorporated into the US National Plant Germplasm System (NPGS), along with new material currently being collected in Ohio.


3.Progress Report:

The original goal of this project is to use microsatellite data to craft a more efficient sampling strategy for the preservation of genetic diversity of green ash trees in Ohio and surrounding states. In addition, this study also seeks to provide some guidelines for the future establishment of a core collection of green ash; i.e., a set of accessions selected to represent most of the genetic diversity of the base collection. Eleven microsatellite markers developed in various species of ash (Fraxinus) have been tested for polymorphisms and their utility for analyzing genetic diversity in green ash. Ten markers were chosen to analyze 35 accessions (1060 individuals); four of these markers have been completed, two are in progress, and three will be completed by December 2013. Preliminary results indicate a high degree of allelic diversity in green ash populations, and within seed crops from individual trees. As USDA researchers and cooperators seek to conserve ash diversity ahead of the devastation caused by emerald ash borer on North American native ash species, this data will improve sampling strategies to ensure the broadest conservation of genetic diversity possible. Undergraduate and graduate students have been trained in DNA extractions, PCR techniques and genotyping analysis.


Last Modified: 10/19/2014
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