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Mary W. George and Robert R. Tripepi

Plant Preservative Mixture™ (PPM), a relatively new, broad-spectrum preservative and biocide for use in plant tissue culture, was evaluated as an alternative to the use of conventional antibiotics and fungicides in plant tissue culture. Concentrations of 0.5 to 4.0 mL·L-1 were tested with leaf explants of chrysanthemum (Dendranthem×grandiflora Kitam), European birch (Betula pendula Roth), and rhododendron (Rhododendron catawbiense Michx.). PPM had little effect on the percentage of explants forming shoots and the number of shoots formed per explant in birch and rhododendron, but dramatically reduced both responses in chrysanthemum. Therefore, the effects of PPM must be evaluated for each species of interest prior to use.

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Raymond O. Miller, Paul D. Bloese, James W. Hanover, and Robert A. Haack

A test of Michigan half-sib progeny of paper birch (Betula papyrifera Marsh.) and European white birch (B. pendula Roth.) was conducted in Michigan to examine species variation in growth, bark color, and resistance to bronze birch borer (Agrilus anxius Gory). Paper birch was superior to European white birch in height and borer resistance at age 12 years from seed. Families of paper birch were identified that grew exceptionally well, had developed white bark within 6 years, and exhibited borer resistance. The magnitude of additive genetic variance and narrow-sense family heritability estimates for paper birch indicated that sufficient genetic variation and inheritance exist to support selection and breeding for height. Paper birch may be an acceptable substitute for European white birch as a landscape species in northeastern North America.

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Thomas G. Ranney and Richard E. Bir

The potential for enhancing flood tolerance of birches by using better adapted rootstock was evaluated. Survival, growth, and physiological responses were compared among flooded and nonflooded container-grown Japanese birch (Betula platyphylla var. japonica Hara. `Whitespire') trees grafted onto each of four rootstock: paper birch (B. papyrifera Marsh), European birch (B.pendula Roth.), river birch (B. nigra L.), and `Whitespire' Japanese birch. Separate studies were conducted in Fall 1991 and Spring 1992. Results showed no consistent differences in net photosynthesis (Pn) or survival among nonflooded plants regardless of rootstock or season, nor, were any symptoms of graft incompatibility evident. Flooding the root system for as long as 44 days revealed considerable differences among the four rootstock, with similar trends for fall and spring. Plants on river birch rootstock typically had one of the highest P rates and stomatal conductance (g,) and, in certain cases, greater mean shoot growth rates and survival of plants subjected to prolonged flooding. Although plants with European birch rootstock had survival rates similar to those of plants with river birch rootstock, plants on European birch rootstock had lower Pn under prolonged flooding, fewer late-formed roots, lower root-tip density after flooding, more abscissed leaves, and greater inhibition of shoot growth of plants flooded the previous fall. Paper and Japanese birch rootstock were most sensitive to flooding and had the lowest survival rate after flooding. However, plants on paper birch rootstock were the only plants whose Pn did not increase significantly when flooding ended; they had the most abscissed leaves during spring flooding and the greatest inhibition of shoot growth in the spring after flooding the previous fall. The four rootstock ranked from most to least flood tolerant were river > European > Japanese > paper.

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Thomas G. Ranney and Mary M. Peet

Leaf gas-exchange and chlorophyll fluorescence measurements were used as indexes for evaluating heat tolerance among five taxa of birch: paper (Betula papyrifera Marsh.), European (B. pendula Roth.), Japanese (B. platyphylla var. japonica Hara. cv. Whitespire), Himalayan (B. jacquemontii Spach.), and river (B. nigra L. cv. Heritage). Gas-exchange measurements were conducted on individual leaves at temperatures ranging from 25 to 40C. River birch maintained the highest net photosynthetic rates (Pn) at high temperatures, while Pn of paper birch was reduced the most. Further study of river and paper birch indicated that the reduced Pn at high temperatures and the differential sensitivity between taxa resulted from several factors. Inhibition of Pn at higher temperatures was due largely to nonstomatal limitations for both taxa. Increases in respiration rates, decreases in maximal photochemical efficiency of photosystem (PS) II (F V/F M), and possible reductions in light energy directed to PS II (F 0 quenching) were apparent for both taxa. The capacity of river birch to maintain greater Pn at higher temperatures seemed to result from a lower Q10 for dark respiration and possibly greater thermotolerance of the Calvin cycle as indicated by a lack of nonphotochemical fluorescence quenching with increasing temperatures. Thermal injury, as indicated by a rapid increase in minimal, dark-acclimated (F 0) fluorescence, was not evident for either paper or river birch until temperatures reached ≈49C and was similar for both taxa.

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Mengmeng Gu, James A. Robbins, Curt R. Rom, and Jason McAfee

Japanese beetle (Popilla japonica Newman) has caused severe damage on a wide range of horticultural crops since its first introduction to the Eastern United States from Japan in 1916. Leaves are skeletonized by adult beetles feeding in masses, which makes this insect damage easy to identify. In Arkansas, Japanese beetle was first trapped in Washington County in 1997 and has reached epidemic proportions in the most recent three years. Leaf skelotonization and feeding preference on eighteen birch accessions by Japanese beetle were recorded in 2003 and 2004. There was a wide range from no feeding (0% leaf skelotonization) to high feeding preference (89% leaf skelotonization). Betula utilis var. jacquemontii and B. papyrifera `Renaissance Upright' had highest preference. Betula pendula `Laciniata' had no feeding damage from Japanese beetle.

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Annette D. Leege and Robert R. Tripepi

A plant regeneration system that is compatible with recombinant DNA techniques is required before birch can be genetically transformed. The goal of this research is to develop a shoot regeneration system from leaf discs of European birch (Betula pendula Roth), since this tissue culture procedure is compatible with current transformation technology. Leaves from microplants were excised from stems, cut into approximately 25 mm2 pieces, and placed on WPM media containing differing ratios of NAA (0, 3, 6, 9 μM) to BA (0, 7.5, 15, 22.5 μM) in a 4 × 4 factorial design. Four replicates, each containing 4 leaf pieces, were used per treatment. After 4 and 8 weeks, data was taken including the percent leaves forming shoots and the number of shoots per leaf disc. Only a concentration of 15 or 22.5 μM BA without NAA stimulated shoot formation on leaf discs. Data on the effects of light, media formulations and tissue orientation will be presented. With a reliable and efficient shoot regeneration system for European birch, genetic engineering of this species is now possible.

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Robert R. Tripepi, Mary W. George, R. Kasten Dumroese, and David L. Wenny

European birch (Betula pendula Roth) seedlings (1+ 0 plugs) were planted in a container growth medium amended with 0, 1.2, 2.4, or 3.6 kg/m3 of a commercial hydrogel and watered either daily or once every 3 or 5 days. When hydrogel was incorporated in the growth medium, shoot and root dry weights and lea area were reduced by 19, 29 and 18%, respectively, compared to controls. Shoot height, stem diameter and shoot:root ratio were unaffected by hydrogel amendment rate. Compared to seedlings in polymer-amended media, plants growing in medium without hydrogel had significantly lower stomata1 conductance and transpiration on fewer than 25% of the measurement dates. Irrigation frequency significantly affected all plant growth Indices and stomata1 parameters; seedlings irrigated daily grew the most and had the highest stomata1 conductance and transpiration. Although polymer-amended media held more water than the medium without hydrogel at all measured tensions, this moisture was retained in the expanded gel rather than being available for plant uptake at higher tensions. The hydrogel appeared to have little benefit for container production of birch.

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M.W. George and R.R. Tripepi

Plant preservative mixture (PPM) is a new broad-spectrum biocide that may be useful for plant tissue culture. The objective of this study was to determine if PPM interfered with adventitious shoot regeneration on leaf explants from several plant species. Leaf explants from Dendranthema grandiflora `Iridon', Betula pendula, Rhododendron catawbiense var. album and R.c. `America' were made from the top two apical leaves on the microshoots. In the first experiment, 0, 0.5, 1, 2, or 4 mL·L-1 PPM were added to species-appropriate regeneration media. In the second experiment, only mum leaf explants were placed on regeneration media containing 0, 0.1, 0.2, 0.3, or 0.4 mL·L-1 PPM. The percentage of explants forming shoots and the number of shoots per regenerating explant were recorded after 4, 6, and 10 weeks, for mum, birch, and rhododendron leaves, respectively. The percentages of shoot regeneration from birch and rhododendron leaf explants were unaffected by up to 4 mL·L-1 PPM, and the number of shoots formed per R.c. album explant were also unaffected by the tested concentrations of PPM. In contrast, the numbers of shoots formed on birch and `America' explants were reduced 48% and 25%, respectively, when 4 mL·L-1 PPM was used in the media. The percentages of shoot regeneration and number of shoots per explant were drastically reduced on mum explants when only 0.5 mL·L-1 PPM was used in the medium. In fact, 0.3 mL·L-1 PPM or higher reduced shoot formation by more than 5-fold. This study demonstrates that the effects of PPM on shoot regeneration from leaf explants are species specific.

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Robert R. Tripepi and Mary W. George

De-inked paper sludge from a newsprint mill was evaluated as a substitute for softwood bark in container media. Whips, 1.2 m tall, of `October Glory' red maple (Acer rubrum L.), European birch (Betula pendula Roth), and `Royalty' crabapple (Malus L.) were planted in 15-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, 0%, or 0%, respectively, bark (by volume). All media contained 10% sand. After 22 weeks, plant heights, trunk diameters, and shoot dry weights were determined. Initial pH of media increased as the amount of paper sludge in the media increased, with the 90% sludge mix having pH 7.2. Paper sludge had a low initial CEC. Physical properties of all sludge-amended media were suitable for tree growth, but media containing 80% or more paper sludge shrank in volume by 10% to 12% by the end of the study. All maple and crabapple trees grown in all sludge-amended media grew as well as those in 80% bark (control mix). In fact, maple and crabapples trees in 40% sludge produced at least 10% and 36% more total shoot biomass, respectively, than trees in 80% bark. Although birch trees grown in 40% or 60% paper sludge grew as well as control plants, those grown in 80% or more sludge were at least 11% shorter and produced 24% less total shoot biomass (leaves, stems, and trunk dry weight) than control trees. These results demonstrated that de-inked paper sludge was a worthy substitute for up to 40% of the bark in a container medium for the three species tested.

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Mengmeng Gu, Curt R. Rom, James A. Robbins, and Derrick M. Oosterhuis

composition Aust. J. Plant Physiol. 27 985 996 Aspelmeier, S. Leuschner, C. 2004 Genotypic variation in drought response of silver birch (Betula pendula): Leaf water status and carbon gain Tree Physiol. 24 517