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  • Author or Editor: Peter J. Zale x
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Phlox is an important genus of herbaceous ornamental plants previously targeted for germplasm development, characterization, and enhancement by the U.S. Department of Agriculture, National Plant Germplasm System. Among Phlox in cultivation, Phlox paniculata is the most widely grown and intensively bred species, but little is known about variation in genome size and ploidy of this species or of related taxa that may be used for germplasm enhancement. The objective of this study was to assess cytotype variation in a diverse collection of cultivars and wild germplasm of P. paniculata (subsection Paniculatae) and of related taxa in subsections Paniculatae and Phlox. The collection included 138 accessions from seven species and two interspecific hybrids. Flow cytometry was used to estimate holoploid (2C) genome sizes and to infer ploidy levels. Chromosome counts were made to calibrate ploidy with genome size for a subset of taxa. Most cultivars were diploid (2n = 2x = 14) and had mean genome sizes that did not vary between subsections Paniculatae (14.33 pg) and Phlox (14.23 pg) although size variation was greater among cultivars within subsection Phlox. Triploid cultivars of P. paniculata, with a mean genome size of 21.36 pg and mitotic chromosome counts of 2n = 3x = 21, were identified. Such triploids suggests previous interploid hybridization within this taxon. Five tetraploid (2n = 4x = 28) cultivars were found in subsection Phlox; all were selections of P. glaberrima ssp. triflora, and had a mean genome size of 25.44 pg; chromosome counts in one of these confirmed they were tetraploid. The putative hybrid Phlox Suffruticosa Group ‘Miss Lingard’ showed an intermediate genome size of 21.21 pg supporting a triploid, hybrid origin of this taxon. Mean 2C genome sizes among wild-collected accessions were similar to values reported for cultivars (Paniculatae = 14.59 pg, Phlox = 14.23 pg), but taxa in subsection Phlox exhibited greater variation that included two tetraploids identified among wild-collected accessions; one, of P. pulchra, had a mean genome size of 26.17 pg, representing the first report of polyploidy in the taxon. This is the first report on genome size for the majority of species in the study. Although genome size could not be used to differentiate taxa in subsections Paniculatae and Phlox, the data provide further insights into cytotype variation of Phlox germplasm useful for plant breeders and systematists.

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U.S. native temperate terrestrial orchids are of horticultural and conservation interest but are considered difficult to propagate from seed due to complex ecological requirements and a variable need for a mycorrhizal fungus. Although there has been significant research on germinating seeds and in vitro seedling development on a variety of temperate terrestrial orchid taxa from around the world, few studies have combined germination experiments with appropriate mycorrhizal fungi that support establishment and continued growth for purposes of ex situ collections development, conservation, or restoration. We conducted experiments with two species of asymbiotically propagated U.S. native orchids [Goodyera tesselata Lodd. and Platanthera blephariglottis (Willd.) Lindl.] to determine the effect of four substrates [Bog garden mix (peat:all-purpose sand) (B), New Zealand sphagnum (NZ), NZ sphagnum + 10% powdered tulip tree wood (NZ/W10), and NZ sphagnum + 50% powdered tulip tree wood (NZ/W50)] and whether inoculating with an appropriate mycorrhizal fungus grown on cellulose sorba rods would support orchid growth and survival in containers and subsequently in outdoor conditions. Morphological measurements and survival data were used in conjunction with real-time quantitative polymerase chain reaction to assess fungal abundance in containers and the impact of fungal presence on growth and survival characteristics. The addition of appropriate mycorrhizal fungi increased the growth and survival of both species across three (NZ, NZ/W10, and NZ/W50) of four substrates. The addition of a mycorrhizal fungus was not a universal solution to improving growth, but the addition resulted in increased abundance of the fungus and better plant performance. This novel experiment suggests that although addition of appropriate mycorrhizal fungi to orchids may increase performance, environmental and horticultural parameters also play an important role in successful orchid cultivation.

Open Access

Breeding and development of ornamental woody plants for specific ideotypes will provide diverse choices to meet specific needs for natural and constructed landscapes. An F1 half-sib family analysis of Magnolia virginiana generated from controlled pollinations was implemented to identify potential juvenile selection strategies for two mature ideotypes: a compact and rounded shrub form (to 2.5 m tall and wide) and a single-stemmed, small tree form (to 4 m tall), both with abundant flowering. The 2-year test was conducted in a container nursery. Fourteen traits were measured in 2007 and 2008, including height at three intervals (July, August, and September), mean branch length and branch count, early and late flower production, collar sprout formation, stem diameter, and branch angle. There were significant differences between F1 half-sib families (P ≤ 0.0001) for all traits. Phenotypic and genetic correlations and narrow sense heritability were estimated for these traits. Phenotypic and genetic correlations showed favorable associations among branch count, caliper, and early flower production. These traits were used to form a selection index for a shrub ideotype. Also, there were positive phenotypic and genetic correlations between height and late flower production, which were both negatively correlated with collar sprout formation. These traits were used to form a selection index for the single-stemmed, small tree ideotype. Narrow sense heritabilities were high for most traits in 2007 but were lower in 2008. Results suggest that selection of phenotypes ranking highest for the traits of interest may yield the desired ideotypes. However, introduction of additional genetic variation through new germplasm accessions may be necessary to maintain breeding progress.

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