Doctoral Dissertations

Date of Award

5-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plants, Soils, and Insects

Major Professor

Robert N. Trigiano

Abstract

The genus Cornus (dogwoods) consists of 58 species that are ecologically and economically important. There were four objectives to this project. Objective one was the development of simple sequence repeats (SSRs) from Cornus kousa 'National' and the application of these markers to assess genetic diversity within kousa dogwood cultivars. Ninety-two SSRs were isolated, optimized and screened. All optimized loci were polymorphic and the number of alleles per locus ranged from 3 to 17. Observed heterozygosity ranged from 0 to 0.3 and expected heterozygosity ranged from 0.38 to 0.91. For objective two, two molecular identification keys were developed for cultivars and breeding lines of C. florida and C. kousa using species specific SSR loci. Most (18 of 24) of the C. florida and all C. kousa accessions were distinguished from each other using SSRs; those that could not were resolved using DNA amplification fingerprinting.The reliability of both keys was determined using five anonymous cultivars for each species, which were correctly identified using the molecular keys. In objective three, 36 SSRs (17 C. florida and 19 C. kousa) were tested on 44 Cornus taxa for cross species transfer and genetic diversity was assessed using the polymorphism information content (PIC). Cross species transferability of SSRs was higher in more closely related species and PIC values ranged from 0 --0.94. Evidence for conserved primer sites within Cornus was revealed by the amplification of SSRs in the taxa examined. For objective four, we combined the ability of honey bees and the self-incompatible nature of dogwood to perform self and cross pollinations. Self pollinations were conducted in 2006 and 2007 with C. florida 'Appalachian Spring' and 'Cherokee Brave' and with C. kousa 'Blue Shadow' and 'Galilean' and low seed set was observed, indicating self incompatibility. Intra-specific crosses of C. florida and C. kousa cultivars and breeding lines were conducted in 2006 -- 2008. Phenotypes of putative hybrids were similar and practically indistinguishable, so dogwood specific SSRs were used to verify a sample of putative hybrids. Results from this project are expected to improve future breeding, population and genetic studies within Cornus.

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