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Samir C. Debnath and Danny L. Barney

, data for the control treatment (0 PGR) were excluded from analysis because all explants failed to respond. Statistical F tests were evaluated at P ≤ 0.05. Differences among treatments were further analyzed using Duncan's multiple range test. Shoot

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Brian K Maynard and Nina L. Bassuk

New shoot growth of Carpinus betulus `fastigiata' was treated with stockplant etiolation and stem banding treatments and sampled for anatomical study at intervals over a 16-week period of greening following etiolation. Shading effects on the anatomy of the stem were also investigated. Numerous anatomical changes were noted with stem age and stockplant treatment. Among these were etiolation effects on the lignification of the secondary xylem, thickness of the periderm, and an increase in the percentage of sclereid-free gaps in the perivascular sclerenchyma, Stem banding increased the widths of the cortex and pith. Concomitant propagation studies revealed significant etiolation, shading, and banding effects on rooting percentages and root numbers. Using multiple linear regression methods rooting capacity was modelled best by linear combinations of the widths of the pith, non-lignified secondary xylem, cortical parenchyma and periderm, as well as the percentage of gaps in the sclerenchymatic sheath remaining non-sclerified. It is proposed that the development of sclereids in potential rooting sites reduces rooting potential. The exclusion of light during initial shoot development retards sclereid development by up to 3 months following treatment, which correlates well with observed increases in the rooting potential of etiolated and/or banded stems.

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A. Raymond Miller and Craig K. Chandler

A protocol was developed for excising and culturing cotyledon explants from mature achenes of strawberry (Fragaria × ananassa Duch.). Cotyledon explants formed callus with multiple shoot buds on agar-solidified Murashige and Skoog media containing several combinations of hormones (1 μm 2,4-D; 10 μm 2,4-D; 1 μm BA + 1 μm 2,4-D; 1 μm BA + 10 μm 2,4-D; 5 μm BA; 5 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μ m 2,4-D; 5 μ m BA + 5 μm NAA; 5 μ m BA + 15 μ m NAA). After three subcultures, only tissues maintained on the medium containing 5 μm BA + 5 μm NAA continued to form shoots. Tissues transferred to other media eventually died (1 μm 2,4-D; 1 μ m BA + 10 μ m 2,4-D; 5 μ m BA; 5 μ m BA + 1 μ m 2,4-D), became unorganized (1 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μm 2,4-D; 5 μm BA + 15 μm NAA), or formed roots (10 μm 2,4-D). Whole plantlets were produced by transferring callus with buds to medium lacking hormones. The rapid regeneration of clonal plantlets from cotyledon explants may be useful for reducing variability in future developmental studies. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); (2,4-dichlorophenoxy) acetic acid (2,4-D); and 1-naphthaleneacetic acid (NAA).

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Sherry Kitto and Jeanne Frett

Hexastylis shuttleworthii is a highly ornamental shade-tolerant evergreen herbaceous plant native to the southeastern U.S. that is difficult to propagate using traditional methods. Micropropagation would make possible the wider distribution of selected clones. Seeds were surface-sterilized and germinated in vitro. Seedling clones were maintained on a MS basal medium containing 1 mg/L BA and were subcultured monthly. Proliferation of clones 2 and 3, maintained on media supplemented with 1, 2.5 or 5 mg/L BA for 6 months, increased slightly with increasing BA concentration; however, proliferation decreased slightly over the experimental period. Rooting medium (perlite, vermiculite, MetroMix 510, Bacto Growers Mix) did not effect microcutting root production or subsequent plant survival. Microcuttings rooted in vitro (67% survival) generated more leaves compared to microcuttings rooted under humidity domes with mist in the greenhouse (8% survival). After rooting in vitro, multiple-shoot clumps (95%) survived better than individual shoots (29%) under greenhouse conditions. Plants were easily established when planted in raised beds in a lath house.

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Thomas H. Yeager

Multiple branched liners of llex vomitoria were greenhouse-grown in 3-liter containers with a common nursery medium and received either 2.5 g N surface-applied in 1 application as Osmocote (18N-2.6P-10K) or a total of 0, 0.5, 1,5 or 2.5 g N per container from a solution that contained N, P and K in a ratio of 6:1:3. The solution fertilizer was applied either 1, 2, 3 or 4 times per week with total N applied per container equally divided among individual applications, After 26 weeks, shoot dry weights were greatest for plants that received 2.5 g of N as either 2 soluble applications per week or as Osmocote applied once at the beginning of the experiment. Plants that received 1.5 g of N applied 4 times per week had similar shoot dry weights. Nitrogen uptake will be calculated to determine if 4 applications par week resulted in greater utilization than 2 applications par week or 1 application of Osmocote during the growing season.

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Carlos Miranda Jiménez and J. Bernardo Royo Díaz

Spring frosts are usual in many of Spain's fruit-growing areas, so it is common to insure crops against frost damage. After a frost, crop loss must be evaluated, by comparing what crop is left with the amount that would have been obtained under normal conditions. Potential crop must be evaluated quickly through the use of measurements obtainable at the beginning of the tree's growth cycle. During the years 1997 through 1999 and in 86 commercial plots of peach and nectarine [Prunus persica (L.) Batsch], the following measurements were obtained: trunk cross-sectional area (TCA, cm2), trunk cross sectional area per hectare (TCA/ha), estimated total shoot length per trunk cross-sectional area (SLT, shoot m/cm2 TCA), crop density (CD, amount of fruit/cm2 TCA), fruit weight (FW, g), yield efficiency (YE, kg of fruit/cm2 TCA), yield per tree (Y, kg fruit/tree) and days between full bloom and harvest (BHP, days). CD and average FW were related to the rest of the variables through the use of multiple regression models. The models which provided the best fit were CD = SLT - TCA/ha and FW = SLT + BHP - CD. These models were significant, consistent, and appropriate for all three years. The models' predictive ability was evaluated for 32 different plots in 2001 and 2002. Statistical analysis showed the models to be valid for the forecast of orchards' potential yield efficiency, so that they represent a useful tool for early crop prediction and evaluation of losses due to late frosts.

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Young Goel Shon, Joong Choon Park, and Byoung Ryong Jeong

Effect of combination and concentration of growth regulators on the regeneration of pepper plant from different explant tissues was studied. Seedlings were grown aseptically in 400 ml glass bottles containing MS agar medium at 26±2C under a 16 h·d-1 photoperiod (2000 lux, florescent lamps). Explants taken from 4 week-old seedlings were cultured under these conditions on 40 ml of MS agar (8 g·liter-1) medium containing 3 g·liter-1 sucrose in a 400 ml glass bottle. Primary and subsequent leaves attached to petiole regenerated better than cotyledon and hypocotyl. Among the combinations of different concentrations of cytokinin and auxin added in the medium, a combination of 5 μM IAA with either 10 μM zeatin or 10 μM BA gave the best regeneration. With these combinations, regeneration frequency of multiple shoots from the primary and subsequent leaves was greater than 70%. Regenerated shoots rooted readily in MS agar medium containing 3 g·liter-1 sucrose and 0.5 μM NAA.

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Jude W. Grosser, Divya Kainth, and Manjul Dutt

. This study reports a more efficient method to induce tetraploids by in vitro treatment of cut stem explants from pummelo selections with colchicine followed by shoot induction through indirect organogenesis. The effect of different colchicine

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Qian Zhang, Jianjun Chen*, and Richard Henny

Pothos (Epipremnum aureum Linden & Andre), a climbing vine with leathery, shiny-surfaced, solid green or variegated heart-shaped leaves, is widely grown as an ornamental tropical foliage plant in hanging baskets or on poles as climbers for interiorscaping. Since pothos easily develops roots from nodes, its propagation is mainly from eye cuttings. Eye cuttings, however, frequently carry diseases from stock plants into production greenhouses. The objectives of this study were to investigate if somatic embryogenesis could be induced from a common cultivar `Golden Pothos' and germinated somatic embryos could be a means of clean propagule production. Using a modified MS medium supplemented with 2 mg·L-1 CPPU or TDZ and 0.2 mg·L-1 NAA or 0.5 mg·L-1 2,4-D, somatic embryos formed directly at cut edges of leaf explants, around petiole and stem explant ends, and along their side surfaces. Most somatic embryos maturated and grew into multiple buds or shoots; some of them developed into whole plants on the original medium. Somatic embryos also germinated and developed into plants on MS medium containing 2 mg·L-1 Zeatin and 0.2 mg·L-1 NAA, MS or 1/2 MS containing 2 mg·L-1 BA with or without 0.2 mg·L-1 NAA. Shoots elongated and roots grew on PGR-free medium. Plantlets grew healthy in shaded greenhouses after transferring to soilless substrates. This study suggests that the established method of somatic embryogenesis can be used to generate disease-free propagules of pothos for production.

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Caula A. Beyl and Cary A. Mitchell

Abstract

Growth in stem length, shoot fresh weight, and leaf surface area of sunflower (Helianthus annuus L.) plants was inhibited by periodic shaking (seismo-stress) or rubbing (thigmo-stress), and by drought-stress treatments. Mechanical- and drought-stress treatment of intact plants reduced xylem exudation from detopped plants. This reduction was accompanied by a reduction in root dry weight only in the case of the drought-stress treatment. Exudate from thigmo-stressed plants contained a broad band of extractable inhibitors some of which co-chromatographed with abscisic acid (ABA). ABA-like substances were not detected in exudate from tall or dwarf controls. Enhanced cytokinin (CK)-like substances were detected in exudate collected from seismo-stressed plants. Shoot tip extracts from thigmostressed plants contained no detectable gibberellin (GA)-like substances, whereas those extracts from unstressed controls contained multiple zones of GA-like activity. Extracts of plant parts most disturbed by a given mechanical treatment yielded no detectable GA-like substances. This study provides evidence that, in addition to auxin and ethylene, other endogenous hormones, particularly GA-like substances, are influenced by mechanical stress in sunflower.