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Lili Zhou, Frank Kappel, Cheryl Hampson, Paul A. Wiersma and Guus Bakkeren

Amplified fragment length polymorphisms (AFLPs) were used to analyze the relationships between sweet cherry (Prunus avium L.) cultivars and selections from the breeding program at the Pacific Agri-Food Research Centre in Summerland, Canada. Six pairs of preselected primers were used for the analysis of a total of 67 cultivars and selections. Scoring the absence and presence of 118 polymorphic DNA fragments produced a unique binary code for each cultivar and selection. Two phylogenetic trees were constructed using these 118 polymorphic fragments, one tree for 55 related cultivars and selections from the Summerland breeding program and the other for 23 self-incompatible cultivars of differing origins. The reliability of AFLP DNA fingerprints was confirmed by correlating relationships revealed by AFLP profiles with known genetic relationships of some sweet cherry cultivars and by a blind test for cultivar identification. Results indicate that AFLP analysis is a good technique to evaluate genetic distance and relationships in a sweet cherry breeding population.

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C. Degani, A. Beiles, R. El-Batsri, M. Goren and S. Gazit

Leaf isozyme banding patterns were studied in 30 cultivars and selections of lychee (Litchi Chinensis Sonn.) by means of starch gel electrophoresis. Polymorphism in aconitase, aspartate aminotransferase, isocitrate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, superoxide dismutase and triosephosphate isomerase is demonstrated for the first time and observations are extended for the previously described polymorphism in phosphoglucose isomerase. In this study we found five groups of cultivars with identical electrophoretic genotypes. The 18 different cultivars were clustered by the UPGMA method into two large clusters and three pairs of similar cultivars. Three cultivars were relatively separate from the clusters. This study shows that isozyme polymorphism is a prevalent phenomenon in lychee, and that isozymes can provide useful genetic markers for lychee cultivar identification and parental analysis.

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Tim Rinehart, Cecil Pounders and Brian Scheffler

Crapemyrtles (Lagerstroemia) are deciduous shrubs or trees with prolific summer flowers. Their popularity is due in large part to low maintenance requirements in sunny climates, wide range of growth habits, disease resistance, and bark characteristics, as well as having a long flowering period (up to 120 days). Once well-established, they are extremely tolerant to heat and drought. Lagerstroemia was first introduced to the southern U.S. from southeast Asia more than 150 years ago, and is comprised of at least 80 known species. Most modern cultivars are L. indica and L. fauriei hybrids. L. speciosa is a tropical crapemyrtle with very large flowers, but lacks cold hardiness. It is a vigorous plant, but only when grown in Hardiness zones 9 or 10. We recently established microsatellite markers for Lagerstroemia and evaluated their utility for verifying interspecific hybrids. Here we verify F1 hybrids between L. indica `Tonto', `Red River', and L. speciosa. We also genotyped two commercially available L. speciosa hybrids. Currently, we are using crapemyrtle SSRs for cultivar identification and germplasm conservation. Future research includes marker-assisted breeding to produce powdery mildew and flea beetle resistant cultivars, as well as improved growth habit and fall foliage color.

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Nicole Gardner and Stan C. Hokanson

The genus Clematis contains many well-known large flowered cultivars, as well as lesser-known nonvining species. Intersimple sequence repeat (ISSR) primers were used to fingerprint 32 vining cultivars and five nonvining species (C. fruiticosa, C. integrifolia, C. heracleifolia, C. hexapetala, and C. recta) for use in assessing genetic relationships and cultivar identification. Four ISSR primers yielded a total of 44 bands in the vining accessions, of which 36 (86%) were polymorphic. The average polymorphism levels were 83% for the cultivars and 94% for the nonvining species. All 32 vining cultivars were distinguished with the use of two ISSR primers, and the five nonvining Clematis species were differentiated with three ISSR primers. A similarity matrix of the cultivars showed low similarity levels between the samples, with an average similarity of 0.28. A UPGMA-derived dendrogram showed no strong groupings among any of the samples. Two cultivars with known parentage, Clematis viticella L. `Betty Corning' and `Sylvia Denny', grouped with one reported parent but not the other, suggesting they are more similar to one parent. `Multi-blue', a sport reportedly arising from `The President' did not segregate near `The President'.

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C.S. Prakash, G. He and R. Jarret

The PCR-based DNA amplification fingerprinting (DAF) approach was used to investigate the evolutionary relationships among 30 U.S. sweetpotato cultivars. Phenogram and pairwise similarity matrix based on Jaccard's coefficients showed relationships among U.S. cultivars and their progenitors to be consistent with the pedigree history. The genetic variability of U.S. cultivars was relatively low (compared to a sample of global collection). Many older U.S. cultivars formed a cluster in the principal coordinate analysis, suggesting their narrow genetic base, but new cultivars, such as `Regal' and `Excel', showed greater divergence. Somatic mutants showed close genetic similarity with their wild types and yet distinct in fingerprint profiles (e.g., `Resisto' and `Copper Resisto'; `Redmar' and `Goldmar'). All cultivars showed unique DAF profiles, and thus, the DAF approach enabled cultivar identification. `Centennial' showed high similarity to major U.S. cultivars such as `Jewel' and `Rojo Blanco'. `Regal' and its open-pollinated offspring `Excel' showed high similarity with each other. `Jewel', the most leading sweetpotato cultivar in the United States, clustered closely to its parent `Nugget' (83%). Carver, a selection from a cross `Centennial' × `Jewel', showed 75% similarity with `Jewel' and 63% similarity to `Centennial'. `Scarlet', a mutant of `Jewel', appeared in the same cluster as `Jewel' but showed only 68% similarity. Our results show that DAF may be an useful approach in elucidating evolutionary relationships among sweetpotato cultivars.

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Terri Woods Starman and Shane Abbitt

The objective was to distinguish between cultivars and evaluate genetic relatedness of poinsettia (Euphorbia pulcherrima) using two methods of DNA fingerprinting—DNA Amplification Fingerprinting (DAF) and Arbitrary Signatures from Amplification Profiles (ASAP). Eleven red poinsettia cultivars were studied, including `Celebrate 2', `Darlyne', `Freedom Red', `Lilo', `Nutcracker Red', `Peterstar Red', `Petoy', `Red Sails', `Supjibi', `V-14 Glory', and `V-17 Angelika'. Amplification was with 10 octamer primers. Gels were visually scored for presence or absence of bands. The 10 primers generated 336 bands. The average number of bands (≈1000 bp) per primer was 34 ranging from 19 to 43. Thirty-one percent of bands were polymorphic and distinguished between each cultivar. The number of unique profiles varied from two to nine. Genetic relationships were evaluated by SAHN cluster analysis based on the distance estimator of Jaccard using the NTSYS-pc program (Numerical taxonomy and multivariate analysis system, version 1.8). The resulting dendrogram closely agreed with known pedigree data. ASAP analysis was used to further assess cultivar identification of two cultivars that were genetically and morphologically similar. Markers were found that separated `Nutcracker Red' and `Peterstar Red'. ASAP analysis separated cultivars within the Freedom series that DAF failed to distinguish. Two cultivars in the Freedom series, `Jingle Bells' and `Marble', were characterized from other cultivars in the series with ASAP.

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Naomi R. Smith and Robert N. Trigiano

Flowering dogwood (Cornus florida L.) is an important tree of forests and urban landscapes in the eastern United States. Currently, there are over 100 cultivars of flowering dogwood commercially available. An identification process based on genotype would be of use to researchers, breeders, and nurserymen, as many cultivars are similar phenotypically. Molecular markers offer a promising way of definitively identifying flowering dogwood cultivars. Amplified fragment length polymorphism (AFLP) is a technique that can be used to generate DNA fingerprints. DNA was isolated from leaves of 17 common cultivars of dogwood and AFLP fingerprints were generated by a Beckman Coulter CEQ™ 8000. Fingerprints were converted to binary data and verified manually. Two drafts of a cultivar identification key were generated based on the corrected, verified binary data and cultivar-specific peaks. Six primer combinations were used to construct all keys and were tested with seven unknown dogwood cultivar samples. Six unknown samples were correctly identified using the keys. Only one unknown, `Cherokee Brave', was unidentifiable with any key. In all cases, some intracultivar variation was observed. A similarity index was calculated and visualized with a tree of genetic relatedness using NTSYSpc. Intracultivar variation was observed in the similarity index as well. This database for cultivar-specific molecular markers will serve as a starting point to which other cultivars can be added and also can be used in breeding applications, patent application and other projects, such as mapping the C. florida genome.

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Prakash P. Kumar, Janice C.K. Yau and Chong Jin Goh

Many Heliconia species are polymorphic with a large number of cultivars. Cultivar identification has been primarily based on morphological differences of the flowers and inflorescences. A protocol was developed to extract DNA from Heliconia leaves and to analyze genetic variation using RAPD. The percentage genetic similarities among Heliconia species, cultivars, and hybrids were determined. Data from 11 primers indicated that the RAPD technique is useful in distinguishing species and cultivars of Heliconia. Using a single 10-mer primer (OPA 18), we were able to generate distinct RAPD profiles for 16 cultivars of H. psittacorum L.f. grown at the Jurong BirdPark, Singapore, a Heliconia Society International depository. Hence, the characteristic profiles generated by RAPD may be used as additional DNA markers for classifying different species and cultivars of Heliconia. The phylogenetic tree derived from the RAPD data showed that all the 16 cultivars examined are closely related to each other, thus providing the first genetic evidence that this large group of cultivars has a common genetic background. Moreover, two triploid cultivars of H. psittacorum—`Iris' and `Petra'—showed identical RAPD profiles with 10 different primers in agarose and polyacrylamide gels, suggesting that they are of the same genotype.

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Darrell Sparks and I.E. Yates

Cellular changes associated with shuck dehiscence and markings deposited on pecan [Carya illinoinensis (Wangenh.) C. Koch] shells were examined by scanning electron and light microscopy. Fruit were sampled at three stages of maturity: 1) shuck and shell fused, 2) sutures separated (shuck opening), and 3) vascular system separated from shuck. Shuck dehiscence involved temporally regulated abscission events with shuck-shell, then shuck-suture, and finally shuck-vascular system separation. Abscission events occurred in a tissue zone common to and continuous among all three separation sites, even though segregated in time. Also, similar cell types and cellular changes were common to the three events. Thus, temporal segregation of abscission events was not due to differences in either tissue type or cellular modifications, but to maturation rate. Structures to become shell markings were single globules filling cells of the shuck inner tissue zone before shuck-shell separation. These globules were deposited on the shell at shuck-shell separation and were morphologically similar to deposits stuck to the dorsal shuck surface. Globules were partitioned differentially between the shuck and shell during shuck-shell separation. Thus, the inner zone of the shuck is an important tissue in pecan nut maturation; it functions as the site for dehiscence and provides markers for cultivar identification.

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C.S. Prakash, Guohao He and Robert L. Jarret

The polymerase chain reaction (PCR)-based DNA amplification fingerprinting (DAF) approach was used to investigate genetic relationships among 30 U.S. sweetpotato (Ipomoea batatas L. Lam.) genotypes including heirloom cultivars and recent releases. Phenogram, pairwise similarity matrix, and principal coordinate plots were developed based on Jaccard's coefficients using band-sharing data generated by seven octamer primers. All cultivars showed unique fingerprint patterns indicating the utility of DAF in cultivar identification. Many heirloom cultivars such as `Creole' and `Porto Rico' were readily differentiated from recently developed cultivars. Modern cultivars such as `Jewel', `Carver', `Nugget', and `Scarlet' exhibited a high degree of similarity reflecting ancestral relatedness. `Regal' and `Excel', recently developed using a population-based breeding approach, showed greater divergence from all other cultivars. Those cultivars, developed as a result of somatic mutations, exhibited high levels of genetic similarity to their normal-type parents and yet had distinct fingerprint profiles. With few exceptions, genetic relationships derived from DAF data appear to be consistent with available pedigree information.