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Margaret R. Pooler

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Hongmei Ma and Margaret Pooler

Ornamental flowering cherry trees (Prunus species) are popular landscape plants that are used in residential and commercial landscapes throughout most temperate regions of the world. Most of the flowering cherry trees planted in the United States represent relatively few species. The U.S. National Arboretum has an ongoing breeding program aimed at broadening this base by developing new cultivars of ornamental cherry with disease and pest resistance, tolerance to environmental stresses, and superior ornamental characteristics. Knowledge of the genetic relationships among species would be useful in breeding and germplasm conservation efforts. However, the taxonomy of flowering cherry species and cultivars is complicated by differences in ploidy levels and intercrossing among species. We have used simple sequence repeat (SSR) markers developed for other Prunus species to screen a diverse collection of over 200 ornamental cherry genotypes representing 70 taxa in order to determine the genetic relationships among species, cultivars, and accessions. Data were generated from 9–12 primer pairs using an automated DNA genetic analyzer (ABI3770), and subjected to UPGMA cluster analysis. Extremely high levels of polymorphism were exhibited among the materials studied, thus indicating that ornamental flowering cherry germplasm has substantial inherent genetic diversity. This information, combined with traditional morphological characteristics, will be useful in determining genetic relationships among accessions in our collection and for predicting crossability of taxa.

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Margaret R. Pooler

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Margaret R. Pooler

Many popular crapemyrtle (Lagerstroemia L.) cultivars grown in the United States are interspecific hybrids between L. indica L. and L. fauriei Koehne. The 22 hybrid cultivars released from the U.S. National Arboretum contain primarily genetic material from L. fauriei PI 237884. Examining the genetic diversity ofL. fauriei specimens in the U.S. is valuable because of the historical and economic significance of the species, the increasing interest it is receiving as a source of new cultivars, and its threatened status in the wild. Our objectives were to examine molecular genetic diversity among L. fauriei accessions using Randomly Amplified Polymorphic DNA (RAPD) and Amplified Fragment Length Polymorphisms (AFLP) markers. Our results indicate: 1) RAPD and AFLP markers are generally consistent in the genetic relationships that they suggest; 2) the L. fauriei germplasm we examined falls into at least three distinct clusters; and 3) the genetic base of cultivated Lagerstroemia could be broadened significantly by incorporating some of this more diverse L. fauriei germplasm into breeding programs.

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Margaret R. Pooler*

The crapemyrtle (Lagerstroemia) is one of the most widely planted and beloved woody ornamental landscape plant in the Southern United States. With hundreds of named cultivars that offer the grower and gardener diverse combinations of flower color, growth habit, and bark characteristics, crapemyrtles are planted primarily for their spectacular bloom in mid to late summer. The crapemyrtle breeding program at the U.S. National Arboretum was started in the early 1960s, and has resulted in the release of 31 improved cultivars of L. indica, L. indica × L. fauriei, and most recently, hybrids between L. indica, L. fauriei, and L. limii. The development of these cultivars, with a focus on the newly released red-flowering cultivars `Arapaho' and `Cheyenne', will be the focus of this poster. Information on Lagerstroemia germplasm, historical perspective, and breeding methodology and goals will be presented.

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Margaret R. Pooler

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Margaret R. Pooler

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Ralph Scorza and Margaret Pooler

Doubled haploid peach [Prunus persica (L.) Batsch] lines were cross-pollinated to produce F1 hybrids. F1 hybrids were evaluated at 3, 7, 8, and 9 years after field planting for tree growth as measured by trunk cross-sectional area, and for fruit production as measured by total weight, total number, and production per unit trunk cross-sectional area. Fruit quality of most F1 hybrids was within the range of quality observed in progeny of standard peach cultivars, and tree growth and productivity were similar to those of standard cultivars. F1 hybrids present the possibility of developing scion varieties that can be produced from seed, thus eliminating the need for grafting scions onto rootstocks in situations where specific, adapted rootstocks are not necessary. They could also be used to develop genetically uniform seed-propagated rootstocks. The use of doubled haploid-derived F1 peach hybrids, however, would require reliable, efficient production techniques.

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Margaret R. Pooler

The U.S. National Arboretum has released over 650 new plant cultivars since it was established in 1927. A key to the success of the plant breeding program has been the voluntary participation of universities and private nurseries in evaluating and propagating new plant material. The cooperative evaluation and stock increase programs play a critical role in the successful testing, introduction, and distribution of new cultivars of landscape trees and shrubs. These integrated cooperative programs depend on the involvement of nurserymen, researchers, botanic gardens, or individuals to evaluate potential new cultivars under diverse climatic conditions and hardiness zones, and wholesale propagation nurseries to increase stock of those cultivars destined for release.

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Margaret Pooler and Hongmei Ma

Flowering cherries belong to the genus Prunus, consisting primarily of species native to Asia. Despite the popularity of ornamental cherry trees in the landscape, most ornamental Prunus planted in the United States are derived from a limited genetic base of Japanese flowering cherry taxa. Controlled crosses among flowering cherry species carried out over the past 30 years at the U.S. National Arboretum have resulted in the creation of interspecific hybrids among many of these diverse taxa. We used simple sequence repeat (SSR) markers to verify 73 of 84 putative hybrids created from 43 crosses representing 20 parental taxa. All verified hybrids were within the same section (Cerasus or Laurocerasus in the subgenus Cerasus) with no verified hybrids between sections.