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Wes Messinger, Aaron Liston, and Kim Hummer

The Pacific Northwest boasts a remarkable diversity of wild currants and gooseberries (Ribes). Of nearly 150 species worldwide, 34 occur in the region. All but two infrageneric taxa are represented, including close relatives of the black currants, red currants, and cultivated gooseberries. High ecological diversity parallels this taxonomic diversity: a Ribes species occurs in nearly every terrestrial habitat, from sea level to above treeline, and from swamp to desert. This diversity is a valuable source of agronomically important genes for the plant breeder. In addition, wild Ribes represent a relatively unexplored source of ornamental shrubs. Habit and habitat of a number of species of interest are described and illustrated. An annotated list of species, subspecies, and varieties native to the Pacific Northwest is presented with discussion of taxonomic proximity to Cultivated varieties, range, natural habitat, and ornamental potential.

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Guochen Yang and Marihelen Kamp-Glass

Exochorda racemosa is an ornamental shrub with white flowers that is spiraea-like, deciduous, and hardy. The buds resemble pearls. Normally it is propagated by seeds, layers, and cuttings of softwood. However, it is a slow process that takes a few years to produce a reasonable size plant for the demanding market. Our objective was to establish a successful in vitro culture and to rapidly multiply this ornamental species. Softwood explant materials were collected from a local nursery and were disinfested with 15% bleach solution and rinsed three times with sterile distilled and deionized water. In vitro cultures were established and maintained in woody plant medium (WPM) supplemented with BA at 0.1 mg·L-1, 3% sucrose, and 0.7% agar with the pH adjusted to 5.8. Then shoots were transferred to the multiplication medium containing BA, CPPU, or thidiazuron (TDZ) at various concentrations. Preliminary results show that explants cultured on medium containing TDZ produced the best shoot proliferation.

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A.L. Shober, C. Wiese, G.C. Denny, C.D. Stanley, and B.K. Harbaugh

Concerns over the environmental impact and economics of harvesting sphagnum and reed-sedge peat have increased the desire to identify acceptable peat substitutes for use in container substrates. This preliminary study evaluated the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates for production of woody ornamental shrubs and assessed potential leaching of nutrients. Walter's viburnum (Viburnum obovatum), sandankwa viburnum (Viburnum suspensum), and japanese privet (Ligustrum japonicum) were grown in 3-gal plastic containers with seven substrates containing (by vol.) 60% pine bark, 10% sand, and 30% sphagnum peat (S), reed-sedge peat (R), and/or composted dairy manure solids (C). Substrate composition had no effect on plant quality ratings for any species, growth index (GI) of walter's viburnum, or shoot and root dry weight of walter's viburnum and japanese privet. However, the GI of japanese privet and sandankwa viburnum was the lowest when grown in substrates containing a high percentage of reed-sedge peat (0S:3R:0C). Substrate effects on average nitrate + nitrite nitrogen leachate losses were minimal over the 88-day leachate collection period. However, the substrate containing the highest proportions of composted dairy manure solids (0S:0R:3C) generally had the highest average ammonium nitrogen and dissolved reactive phosphorus losses compared with other substrates. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown woody ornamental shrub species based on growth and quality. However, average nutrient losses from containers differed depending on the peat or peat substitute used to formulate the substrates.

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Hua Zhou, Fang-Yun Cheng, Jing Wu, and Chaoying He

Arabidopsis thaliana Flowering locus T (FT) homologs have been shown to be sufficient to trigger flowering and to regulate flowering time in a wide range of plants. However, such a homologue for the perennial ornamental shrub tree peony has not yet been characterized. In this study, we isolated PsFT, which is a closely related FT homolog from reblooming [Paeonia ×lemoinei ‘High Noon’ (HN)] and nonreblooming [P. ×suffruticosa ‘Luo Yang Hong’ (LYH)] cultivars of tree peonies, and identified its potential role in the regulation of flowering time. The PsFT alleles from the two cultivars encode the same protein, which indicates that the polymorphisms observed in the coding region do not contribute to the distinct flowering phenotypes of HN and LYH. Comparative analyses of the PsFT expression patterns in HN and LYH indicated that PsFT might be associated with reblooming. Transgenic A. thaliana plants ectopically expressing PsFT exhibited a phenotype that included significantly early flowering compared with the wild-type (WT) plants. Taken together, our data provide valuable clues for shortening the juvenile periods and extending the flowering periods of perennial woody plants, such as tree peonies.

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D. Sankhla, T.D. Davis, N. Sankhla, and A. Upadhyaya

This report describes an efficient in vitro regeneration protocol for H. patens (firebush), a heat-tolerant ornamental shrub native to tropical and subtropical America. Shoot cultures were initially established using shoot tips placed on MS-revised medium containing 2.3 μM 2,4-D, 2.3 μM kinetin, and 0.25% polyvinylpyrrolidone. Other types of explants (nodal and internodal segments, leaf pieces, floral buds) did not regenerate shoots when placed on this medium. Two-month-old plantlets derived from the shoot tips were subcultured on MS medium supplemented with 0.5 μM thidiazuron (TDZ), and within 3 to 4 weeks, some callus was produced at the root–shoot junction. When this callus, with a small portion of the root and shoots, was placed on MS medium with 0.05 μM TDZ and 0.01 μM ABA, prolific shoot formation occurred within 3 to 4 weeks followed by root formation. By regular subculturing every 5 to 6 weeks, hundreds of plantlets have been obtained over the past 3 years with no apparent decline in regeneration potential. Addition of activated charcoal (0.5%) to the culture medium has greatly improved growth of the plantlets.

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Rolston St. Hilaire and Carlos A. Fierro Berwart

Mussaendas (Mussaenda spp.) are ornamental shrubs, and some cultivars are difficult to root. This study was conducted to explore how adventitious roots initiate and develop in the cultivar Rosea, and to determine if anatomical events are associated with difficulty in rooting stem cuttings. Stem cuttings were treated with 5, 10, 15 mm 1H-indole-3-butyric acid (IBA), or distilled water, and sampled every 2 days over 26 days to observe adventitious root formation and development. For analysis by light microscopy, the basal 1 cm of cuttings was embedded in wax and stained with safranin-fast green. Adventitious roots initiated from phloem parenchyma cells and from basal callus in nontreated cuttings. Cuttings treated with 15 mm IBA had a mean of 18 root primordia per basal 1 cm of cutting after 10 days. Root primordia were not observed in non-treated cuttings at 10 days. Root primordia that developed in non-treated cuttings lacked clear vascular connections. These results suggest that non-treated cuttings are difficult to root because few primordia are produced.

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Houchang Khatamian and Alan Stevens

During the Spring of 1992 a survey of over 2000 respondants was conducted as personal interviews at Flower/Garden Shows in Atlanta, Kansas City, Los Angeles, Philadelphia and Portland.

When asked how the plants you buy are packaged? Nine percent of the Los Angeles (LA) sample said they purchased trees as balled and burlapped (B & B) while over 40% of the consumers from the other regions purchased trees as B & B. Over 40% of all respondents purchased shrubs in “container”.

When asked how would you like to have landscape plants packaged? While only 31% of the LA sample chose to purchase trees as B & B, over 70% of the consumers from other regions preferred to buy in a B & B form. More than 50% of all respondents also preferred to purchase trees in “Container”. By a two to one margin consumers chose to purchase ornamental shrubs in “Container”. Regardless of the region of the country, “bare-root” and “plastic package” were least desired. About 1/2 of the respondents were couples, 80% owned their own homes, over 50% had an income of $25,000 to $75,000 and more than 75% did own plantings.

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Jeff Gillman, Michael Dirr, and Kristine Braman

Buddleia species are attractive ornamental shrubs whose major cultural problem is infestations of the two-spotted spider mite. Two factors, drought stress and leaf pubescence, were examined for their effects on spider mite infestations. Drought stress was examined by placing 20 plants into a randomized block design and stressing ten of the plants. No differences in mite life parameters were found, although there was more uninfested area in nonstressed plants. This was probably due to the nonstressed plants' ability to outgrow the spider mite infestation. Leaf texture was examined by placing four female spider mites on 5 leaf disks of 37 cultivars and species of Buddleia and counting the number of eggs laid after 96 hours. There was a strong correlation between leaf pubescence and number of eggs laid. In a second experiment, using a shell vial with a leaf placed underneath the lid and five female spider mites in the vial itself, leaf pubescence was either removed with facial peel or left. In all cases but one, the removal of pubescence increased the number of eggs laid by the spider mites.

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Samuel G. Obae, Mark H. Brand, and Richard C. Kaitany

Japanese barberry (Berberis thunbergii DC.) is a popular ornamental shrub used in garden and urban landscaping. Currently there are over 60 B. thunbergii cultivars in the market. To better distinguish its cultivars, we used the amplified fragment length polymorphism (AFLP) technique to develop DNA marker profiles for 59 cultivars and hybrids. These markers were used to authenticate the trueness-to-name of B. thunbergii cultivars in production and in the market, control for intracultivar genetic variants, and develop a molecular key to identify cultivars approved for importation in Canada. Polymorphic markers from seven primer combinations were able to clearly differentiate 57 of 59 cultivars evaluated. Two cultivars, Aurea and Aurea Nana, could not be differentiated because they had identical marker profiles. Among the 274 plants tested, 263 were confirmed to be true-to-name and correctly labeled, whereas 11 plants could not be confirmed true-to-name. Seven of the 20 cultivars evaluated exhibited detectable intracultivar genetic variation. ‘Crimson Pygmy’ had the highest number of plants exhibiting genetic variability. Overall, nursery producers and retailers do not appear to be mixing or mislabeling cultivars. A molecular key developed from a subset of 25 markers was able to accurately identify and differentiate the 11 B. thunbergii cultivars approved for importation in Canada. This key could be used in a cultivar verification program to facilitate international trade of B. thunbergii cultivars where wheat rust is a concern.

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Calvin Chong, R.A. Cline, D.L. Rinker, and O.B. Allen

`Eight deciduous ornamental shrubs-deutzia (Deutzia gracilis Siebold & Zucc.), dogwood (Cornus alba L. `Argenteo-marginata'), forsythia (Forsythia × intermedia Zab. `Lynwood Gold'), ninebark [Physocarpus opulifolius (L.) Maxim.], potentilla (Potentilla fruticosa L. `Red Ace'), privet (Ligustrum vulgare L.), rose (Rosa L. `John Frank. lin'), and weigela [Weigela florida (Bunge) A. DC. `Variegata Nana']—were grown in trickle-irrigated containers with 100% bark (control) or with bark and 33%, 67%, and 100% (by volume) of each of three sources of spent mushroom compost (unweathered, weathered, and unweathered compost leached with water). Despite large variation in species growth response to sources and levels of compost, most grew equally well or better in the compost-amended regimes than in 100% bark and were influenced little, or not at all, by initial or prevailing salt levels in the media. Shoot and root dry weight of dogwood, forsythia, ninebark, rose, and weigela (all sources), and shoot dry weight of deutzia and potentilla (weathered source only), increased linearly or curvilinearly with increasing compost levels. The reverse relationship occurred (all sources) in shoot and root dry weight of privet and root dry weight of weigela and potentilla. Leaf nutrients (N, P, K, Ca, Mg, Fe, Mn, and Zn) tended to increase with increasing compost levels, but not all species showed this response with all nutrients. Regardless of compost source or level, all shrubs were of marketable quality when harvested, except privet, which showed leaf chlorosis in all compost-amended regimes.