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  • Author or Editor: M.W. George x
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Abstract

Tibouchina urvilleana is a flowering tropical shrub with large (60–80 mm diameter) violet-blue flowers borne in terminal branched panicles. The foliage is downy with red margins. Tibouchina blooms from mid-summer into late fall. The shrub withstands “a few degrees of frost” (1). Tibouchina has potential for wider use although container production has been limited since severe pruning is required to maintain its shape. Growth retardants may aid in commercial production of compact Tibouchina plants.

Open Access
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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.

Free access
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Seeds of `Berken' mung bean [Vigna radiata (L.) R. Wilcz.] were surface-sterilized with NaOCl and then either aerated 24 hours before sowing (routine procedure), planted immediately after the NaOCl treatment, or treated with hot cupric acetate and antibiotics before planting. Nine- or 10-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed upper stems or wilted leaves. None of the seed treatments completely eliminated the pathogen, but the combination of hot cupric acetate plus antibiotics reduced the quantity of diseased cuttings to 3.3%. A white and two yellow-pigmented (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 strain was nonpathogenic. Stems of plants inoculated with the white strain turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the Y1 strain wilted after 7 days. Electron microscopy, fatty acid analysis, and standard biochemical and physiological tests were used to identify the white strain as Pseudomonas syringae pv. syringae van Hall and the Y1 strain as Curtobacterium flaccumfaciens ssp. flaccumfaciens (Hedges) Collins and Jones. These results emphasize that seeds of mung bean should be checked for seedborne pathogens to avoid experimental artifacts.

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Mature peach trees were grown in six different-sized vegetation-free areas (VFAs) (0.36 to 13 m2) with and without stage 3 drip irrigation for 6 years. As VFA size increased, so did the trunk cross-sectional area, canopy diameter, total yield/tree, large fruit yield/tree, and pruning weight/tree. The yield efficiency of total fruit and large fruit initially increased with the increasing size of VFAs and then remained stable over the range of VFAs. Applying supplemental irrigation increased yield of large fruit and leaf N percentage in all VFAs. Cold hardiness was not affected by VFA size or irrigation treatment. The smaller VFAs resulted in smaller, equally efficient trees. Sod management was an effective, low-cost approach to controlling peach tree size, and, when combined with irrigated, high-density production, potentially increased productivity.

Free access

Pulp and paper sludge is a byproduct of paper production, yet this fibrous material may be suitable as an alternative amendment for peat moss in container media. Newsprint mill sludge was composted 6 weeks and cured before use. One-year-old seedlings of lilac (Syringa vulgaris L.) and amur maple (Acer ginnala Maxim.) as well as rooted cuttings o cistena plum Prunus × cistena Hansen) were planted in 3-liter pots that contained a barksand (2:1 by vol) mix, 25% or 50% peatamended media, or 25% or 50% sludge-amended media. After 14 weeks outdoors, shoot dry weight and changes in plant height were measured. All species planted in sludge-amended media grew as well as those potted in peat-amended media or the bark:sand mix. In fact, some species grew best in sludge-amended media. Lilac seedlings planted in 25% sludge produced almost double the amount of shoot dry weight and were 80% taller than plants in the bark:sand mix or 25% peat. Maple plants grown in 500% sludge produced over 100% or 3590 more shoot dry weight than those grown in 25% or 50% peat-amended media, respectively. Plum cuttings pottedin25910 sludge grew at least 53% taller than plants grown in either peat-amended medium. These results indicate that composted newsprint sludge can be used as a peat moss substitute in a container medium for the landscape plants tested.

Free access

A plantless system using subirrigation was developed to measure water absorption and loss in soilless media amended with hydrophilic polymers, a wetting agent, or combinations of these amendments. Peat-perlite-vermiculite and bark-peat-perlite controls achieved 67% and 52% of container capacity, respectively, after 20 daily irrigation cycles. Maximum water content of amended media was 78% of container capacity. Adding only a hydrophilic polymer did not increase total water content significantly. Adding a wetting agent increased water absorption in both media. However, when hydrophilic polymer and wetting agent were present, the medium absorbed more water than with wetting agent alone. More extractable water was removed from media containing wetting agent. Water loss rate by evaporation was not affected significantly by medium, hydrophilic polymer, wetting agent, or any combination of these variables.

Free access

The objective of this study was to determine if selected strains of Agrobacterium could infect microshoots of Rhododendron catawbiense. Fifteen microshoot stems of R. catawbiense var. album `America', `Joe Paterno', and `Cunningham's White' were inoculated with two drops (about 25 μL) of wild type Agrobacterium tumefaciens strains C58 or B6 or with wild type A. rhizogenes strain E8/73. Five control shoots were inoculated with 1.2 mM KH2PO4 buffer. Microshoots were grown on woody plant medium (WPM) supplemented with 4.9 μM 2iP. Six weeks after inoculation galls that formed were excised from the microshoots and placed on WPM that lacked plant growth regulators but contained 300 mg·L-1 cefotaxime. In another study, these wild-type bacterial strains were genetically modified by inserting the pBINm-gfp5-ER plasmid, which contained genes coding for NPTII and green fluorescence protein (GFP), into the bacteria. These modified strains were inoculated on 15 stems of the three rhododendron cultivars and one variety. Calluses that formed were excised, placed on basal WPM with cefotaxime, and allowed to proliferate. Wild type C58 induced galls to form on `Joe Paterno', R.c. album, and `Cunningham's White' stems, whereas wild type B6 caused galls to form only on the latter two types of rhododendron. Wild-type E8/73 failed to induce gall formation on the rhododendrons. Only genetically modified B6 caused galls to form on only `Cunningham's White' microshoots (seven of 15 inoculated stems). Three of these galls fluoresced green under ultraviolet light. Physical presence of the NPTII and GFP genes in the plant genome was determined by polymerase chain reaction. This study demonstrated that R. catawbiense is susceptible to Agrobacterium infection, and this plant can be genetically transformed.

Free access