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United States Department of Agriculture

Agricultural Research Service

Title: Diversity and Phylogenetic Relationships of the Citrus Varieties Collection

Authors
item Barkley, N - UC RIVERSIDE
item Roose, M - UC RIVERSIDE
item Krueger, Robert

Submitted to: International Society of Citriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2004
Publication Date: July 1, 2007
Citation: Barkley, N.A., Roose, M.L., Krueger, R. 2007. Diversity and Phylogenetic Relationships of the Citrus Varieties Collection. International Society of Citriculture Proceedings 178-182

Interpretive Summary: Germplasm collections are quite important in furthering agricultural research and food security. However, under certain circumstances the relationships between the accessions in the collection are not clear. This can lead to redundancies, gaps, and decreases in efficiency. Recently, it has become possible to assess the relationships between accessions using various molecular marker systems. Twenty-five simple sequence repeat (SSR) markers were used to detect molecular polymorphisms among 370 Citrus accessions from the Citrus Variety Collection located at The University of California, Riverside, which is used as a cooperative resource by the NCGRCD. Phylogenetic relationships between the Citrus accessions and related taxa were determined by constructing a neighbor-joining tree by utilizing the genetic distance data generated by the analysis. Additionally, individual Citrus accessions were probabilistically assigned to populations or multiple populations if their genotype indicated admixture by using a model-based clustering approach. These separate analyses (distance and model based) both support the hypothesis that there are only a few naturally occurring forms of Citrus and the rest of the Citrus species are hybrids of these naturally occurring forms. This information provided additional information regarding the probable origin of various accessions in the collection. In some cases, our previous suppositions was confirmed whereas in other cases a new light was cast upon the accessions.

Technical Abstract: Twenty-five simple sequence repeat (SSR) markers were used to detect molecular polymorphisms among 370 Citrus accessions from the Citrus Variety Collection located at The University of California, Riverside. The number of alleles detected per locus ranged from three to thirty. A total of 298 alleles were detected with an average of 11.88 alleles per locus and an average polymorphic information content (PIC) value of 0.633. The proportion of shared alleles was utilized as a statistical measure for determining genetic distance between all pairwise combinations. Phylogenetic relationships between the Citrus accessions and related taxa were determined by constructing a neighbor-joining tree by utilizing the genetic distance data. Additionally, individual Citrus accessions were probabilistically assigned to populations or multiple populations if their genotype indicated admixture by using a model-based clustering approach. These separate analyses (distance and model based) both support the hypothesis that there are only a few naturally occurring forms of Citrus and the rest of the Citrus species are hybrids of these naturally occurring forms.

Last Modified: 7/31/2014
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