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J.W. Van Sambeek and John E. Preece

Hybrid poplar is traditionally established using dormant stem cuttings in tilled soils followed by chemical or mechanical weed control. In 1996, we initiated a study to evaluate the effects of site preparation and four weed control treatments on growth and morphology of three hybrid poplar clones established on a 0.2-ha tall fescue field in southern Illinois. Site preparation included application of 2000 kg/ha of 12N-12P-12K. The experiment was arranged as a split-split plot. Main plots were closely mowed tall fescue or tilled to remove the grass sod. Within each main plot, weed control treatments were applied to 1-m wide strips in rows 2.4 m apart. Weed control treatments included porous black film, solid black film, and solid white film, and a control treatment of 3.7 L/ha of glyphosate applied each spring. On 15 Apr. 1996, three 25-cm-long dormant stem cuttings from each of three clones were randomly planted 15 cm deep every 1.8 m within each row. Clonal differences existed after the first year for survival, number of stems, stem height, stem basal diameter, and stem volume, but not for number and total length of lateral branches. Nearly all tree growth measurements analyzed during the first 3 years had a highly significant interaction between type of site preparation and method of weed control. With polyethylene films, tree survival exceeded 90% on both the tilled ground and grass sod sites after 3 years; however, with the herbicide treatment survival averaged only 18% in the grass sod and 51% in tilled soil. Excluding the herbicide treatment, tree growth was better in the grass sod than in the tilled soil. Tree growth using porous black polyethylene film was usually less than that with either of the two solid polyethylene films. The best tree growth was found with a grass sod and solid white polyethylene film for weed control.

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Michael Wisniewski, Jörg Sauter, Valerie Stepien, and Les Fuchigami

Sublethal heat stress has been shown to decrease or eliminate deep supercooling of flower buds in woody plants and to release plants from endodormancy. Experiments were conducted to characterize the effect of heat stress on endodormancy and ecodormancy in peach (cv Loring) and two hybrid poplars. Protein synthesis (de novo) and patterns of protein expression were also monitored. In order to determine optimum treatment temperatures, shoots, collected September-March, were exposed to a range of temperatures (35-60 C) under wet or dry conditions for 1-6 h. Shoots were then placed in the greenhouse and cumulative budbreak was monitored over 4 weeks. Samples of bud and bark tissues were collected during and up to 72 h after heat treatment for SDS-PAGE analysis. Data indicate: 1) twigs must be immersed in water for the heat treatments to be effective; 2) heat treatments resulted in a release from endodormancy and a decrease in thermal units needed for budbreak during ecodormancy; 3) 40 C for 2-4 h was optimum in fall and late winter whereas 45 C was the optimum temperature to induce budbreak in midwinter; 4) optimum temperature for peach floral buds (37.5 C/2h) was lower than for vegetative buds (40 C/4h), and 5) heat treatments also decreased cold hardiness. Protein synthesis decreased significantly following heat treatment but was significantly greater than controls (room temp) 24-48 h after heat treatment.

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Richard Meilan, Caiping Ma, and Steven H. Strauss

We assessed the stability of transgene expression in 79 transgenic lines (i.e., transformation events) of hybrid poplars during several years of field trials. The transgenic lines were comprised of 40 lines of hybrid cottonwoods (P. trichocarpa × P. deltoides) that were grown at three field sites, and 39 lines of hybrid aspens (section Leuce, P. alba × P. tremula) that were grown at a single field site. All the lines were transformed with a binary construct that included two genes that confer tolerance to glyphosate (GOX and CP4), a gene encoding resistance to the antibiotic kanamycin (nptII), and a visible marker gene (GUS). Agrobacterium tumefaciens was used for transformation; callogenesis and organogenesis occurred under kanamycin selection. In addition to repeated applications of herbicide to test stability of transgene expression, for the first time, we challenged ramets of 40 lines that had not previously been tested for herbicide resistance in their fourth season of vegetative growth. We report on the stability of herbicide resistance and GUS expression and evidence for somaclonal variation in growth and leaf morphology.

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Daniel C. Milbocker

Pyrus calleryana, Decne, `Aristocrat'; Cryptomeria japonica, D. Don; Populus maximowiczii, Henry × `Androscoggin' and Koelreuteria bipinnata, Franch. trees were grown in low-profile containers. The optimum height and width of these containers was 20 to 30 cm and 84 cm, respectively. Pine bark and mixtures containing 50% or more of pine bark were preferable to mixtures containing leaf mold for filling the containers because the former weigh less. Roots penetrated pine bark mixtures better than sphagnum peat mixtures and also retained their shape better during transplanting. When grown in low-profile containers, trees grew fibrous root systems; after transplanting, roots grew downwardly radial and trees were able to withstand extremely difficult landscape conditions.

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Matthew A. Escobar, Andrew Shilling, Pine Higgins, Sandra L. Uratsu, and Abhaya M. Dandekar

regulation with young leaves, fruit, and flowers possessing the highest PPO transcript levels in several different species ( Steffens et al., 1994 ). In some plants, most notably tobacco, tomato, and hybrid poplar ( Populus trichocarpa × P. deltoides ), PPO

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Shawna L. Daley, William Patrick Wechter, and Richard L. Hassell

after 10 d in both starches and soluble sugars of decapitated hybrid poplar ( Populus maximowiczii × P. nigra ). Another study of defoliated cranberry ( Vaccinium macrocarpon ) uprights showed no effect of defoliation on total nonstructural

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Suping Zhou, Roger Sauve, Tara Fish, and Theodore W. Thannhauser

precursor (1–1-2.4.20.1, 1.68-fold-up). Extensive deposition of secondary cell wall materials prevents cell expansion ( Lagrimini et al., 1987 ). Plant growth in the transgenic hybrid poplar ( Populus alba × P. grandidentata ) overexpressing a UDP

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Xiaoling He, Susan C. Miyasaka, Maureen M.M. Fitch, Sawsan Khuri, and Yun J. Zhu

et al., 2005 ). Hybrid poplar ( Populus × euramericana ) transformed with a wheat OxO gene exhibited enhanced disease resistance against the fungus Septoria musiva ( Liang et al., 2001 ). Because OA is a toxin secreted by these pathogenic fungi, it

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Ed Stover, Richard R. Stange Jr., T. Gregory McCollum, Jesse Jaynes, Michael Irey, and Erik Mirkov

resistance in citrus. D4E1, a 17 amino acid synthetic AMP, which forms a beta sheet ( Lucca et al., 1998 ), was among the most active AMPs in our in vitro assays. D4E1 was active against AT expressed as a transgene in hybrid poplar [ Populus tremula × P