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A Genetic Study of Pigmented Cornus kousa Cultivars

R. N. Trigiano, M.H. Ament and M.T. Windham

Mailing Address:
Department of Entomology and Plant Pathology
The University of Tennessee
Knoxville, TN 37996-4560

A paper from the Proceedings of the 12th Metropolitan Tree Improvement Alliance Conference (METRIA 12), Landscape Plant Symposium: Plant Development And Utilization, held in Asheville, NC, May 23-25, 2002, co-sponsored by the North Carolina State University, North Carolina Division of Forest Resources, USDA Forest Service Southern Region, North Carolina Landscape Association, North Carolina Association of Nurserymen, The Landscape Plant Development Center, The North American Branch of The Maple Society, and The International Ornamental Crabapple Society.


Introduction

Cornus kousa Hance cultivars are becoming more popular as landscape plants since they are generally highly resistant to many diseases (e.g. powdery mildew and dogwood anthracnose) that plague C. florida L. (flowering dogwood) cultivars. They are now available with either white, cream, pink or red bracts and bloom about a month after flowering dogwood However, there is an increased chance of mistakes in the trade, such as labeling, with rapid introduction of similar types of pink and red Kousa dogwoods. Several Tennessee nurserymen have commented on the vegetative similarities between 'Miss Satomi' and 'Heart Throb' (pink-to-red bracts) - each had the same leaf architecture (size, shape and color of the leaves), growth habit and growth rate. These dogwood growers could not tell the two cultivars apart. 'Miss Satomi' has medium pink bloom in cooler climates (blotchy pink in warmer) and 'Heart Throb' is purported to have deep red bracts. There are a number of other commercially available Kousa dogwood cultivars with red bracts. Although some of these cultivars are readily and easily recognizable, others appear quite similar and/or nearly identical. This project was undertaken to genetically examine six red-bracted cultivars using a DNA profiling technique.

Materials and Methods

'Christian Prince' (PRI), 'Rosabella' (ROS), 'Little Beauty' (LB) (also variegated), 'Heart Throb' (HT), 'Miss Satomi' (SAT) and "Samaritan' (SAM) are red-bracted cultivars and were ordered from several wholesale nurseries on the east and west coast of the United States. Some cultivars were obtained from several different nurseries. At least three specimens of each individual cultivar were included in the initial DNA profiles, but later experiments included multiple entries of only cultivars that demonstrated very similar or identical DNA profiles. A total of 24 plants of six cultivars were used in the analysis.

Young, not fully expanded leaves were collected in early morning from plants of each cultivar and stored at -75C until needed. Total DNA was extracted using a Puregene Kit (Gentra Systems, Minneapolis, MN). DNA amplification fingerprinting (1) was used to profile the genomic DNA of the cultivars. The reactions mixtures contained one of the following four primer sequences (5'-3'): GTATCGCC, AATGCAGC, GACGTAGG or GTAACGCC. Amplification products were separated electrophoretically on a 0.45-mm thick, 10%-7M urea acrylamide gels.

Amplification profiles (bands in the gel) were examined on a light box and those bands of 700 base pairs (bp) or less scored as either present (1), absent (0) or questionable (9). These binary data were entered as unordered, non-directed, and unweighted characters by primer. The data set was analyzed with the Numerical Taxonomy and Multivariate Analysis System (NTSYS-pc, 2.0), version 2.0 (Exeter Software, Setauket, New York) by first calculating Jaccard similarity coefficients and then assembling a dendrogram using Unweighted Pair Group Cluster Analysis Using Arithmetic Means (UPGMA).

Results and Discussion

Amplifications with the four primers generated clear and reproducible DNA profiles for all individual plants of all cultivars. A total of 117 loci (bands) were considered in the statistical analysis. The DNA profiles from plants of HT and ROS were identical regardless of nursery origin. The DNA products from two plants of SAT were also identical to HT and ROS and five additional plants of SAT differed by only one minor band. The similarity indices ranged between 0.99 and 1.00 for cultivars HT, ROS and SAT supporting the contention that HT, ROS and SAT are the same, but have been released under different names. An alternative hypothesis is that three distinct cultivars were originally released, but through confusion, one has become dominant in the trade (4). The DNA profiles generated from plants of cultivars LB, SAM and PRI were dramatically different from each other and from those produced for cultivars HT, ROS and SAT (similarity indices between 0.65 and 0.75). Cluster and principal coordinate analysis also indicated that cultivars HT, ROS and SAT were essentially the same and that cultivars LB, SAM and PRI were distinctly different. In a similar study, DAF profiles were used to determine that the white-bracted 'Barton' and 'Cloud Nine' flowering dogwood cultivars were the same (4). In this same study, arbitrary signatures from amplification profiles [(ASAP (2)], a technique that detects genomic differences more efficiently than DAF (3), could not distinguish the two cultivars of flowering dogwood.

Analysis of genomic DNA of flowering and kousa dogwoods as well as other ornamental plants has become an important tool for obtaining and protecting patent rights for cultivars and other plant materials. We anticipate that the usage of this type and emerging DNA technologies to separate and identify closely related phenotypes in the woody plant industry will become more routine in the near future (4). We encourage nurserymen and plant breeders to employ DNA profiling of new materials before patent applications and cultivar releases to avoid confusion of similar plants in the trade.

Literature Cited

  1. Caetano-Anolles, G. et al. 1991. Bio/Technology 9:553-557.
  2. Caetano-Anolles, G. and PM. Gresshoff. 1996. Biotechniques 20:1044-1056.
  3. Trigiano, R.N. et al. 1998. J. Amer. Soc. Hort. Sci. 123:642-646.
  4. Windham, M.T. and R. N. Trigiano. 1998. J. Environ. Hort. 16:163-166.

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