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  • Author or Editor: John E. Preece x
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Exogenously applied plant growth regulators (Table 1) may act by altering endogenous hormone systems, influencing interactions among these systems, or by disrupting portions of the plant (23). This activity generally occurs because the applied growth substance substitutes for a hormone, affecting its synthesis, catabolism, conjugation, transport, or receptor site(s).

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Softwood shoots can be forced from sections of branches of trees or from basal stems of shrubs by cutting into ≈40-cm lengths and placing these segments horizontally in flats filled with perlite. We have had our best success using stems that are >1.5 cm in diameter. Although the best environment that we have found for producing the most and longest softwood shoots is under intermittent mist, this is unacceptable for producing explants because of microbial contamination. Rather, for micropropagation, watering must be done two to three times a day and care must be taken to avoid water spray onto the stem segments or the subsequent softwood growth. Irrigation can be by hand or by using drip irrigation. For trees, using the basal portions of large branches allows for selection of shoots from within the “cone of juvenility.” Theoretically, these should propagate better than shoots taken from the outer, more adult portions. Although late winter through spring are the best times for forcing, some shoots will grow if the stem sections are harvested nearly any time of the year, except for October through December in southern Illinois.

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Under natural conditions, hyacinths (Hyacinthus orientalis L.) propagate vegetatively at a slow rate by the production of clusters of daughter bulbs (4, 12). For commercial propagation, scooping, scoring (4, 5, 12), and coring (2, 4) are used because they result in more uniform progeny than natural propagation (4). Hyacinths also can be propagated asexually using in vitro techniques (10, 11). This artificial propagation destroys the apical growing point and requires special treatments and environmental conditions.

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In an effort to improve higher education, most states now require non-graded assessment of students enrolled in publicly funded universities. Assessment may be across the curriculum or within a major at graduation, yearly, or during individual courses or lectures. I have used two assessment techniques in my classroom that are effective and require a minimum of time. These techniques encourage student participation in class and allow for non-graded anonymous assessment in a manner that the students take very seriously. During the first class of the term students are handed filing cards and given 5 minutes to write their course objectives. By comparing their objectives with mine, I am able to react to student interests and needs in a constructive manner. At the end of one out of three lectures per week, students are given 1-2 minutes to write the “muddiest point” of the day's lecture. This enables the instructor to determine which points need further clarification. Discussion will focus on these techniques and their implications for learning horticulture at both the graduate and undergraduate levels.

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Two nongraded techniques are described that assess student expectations and learning in horticulture classes. These involve anonymous, in-class student responses that can encourage and enhance interaction, communication, and learning without being a burden to the instructor. During the first class meeting, students were given 5 minutes to write their course objectives onto filing cards. By summarizing their objectives, reviewing them with the class at the beginning of the next period, and comparing their objectives with mine, I was able to react to student interests and needs in a constructive manner. About once per week at the end of a lecture, students were given 3 minutes to write the “muddiest point” of that lecture. This enabled me to clarify points orally, in writing, or by specific reading assignments. If the instructor responds in a timely manner, these assessment techniques will be taken seriously by the students. Such techniques can increase interest, understanding, and the perception that students can have a positive influence on the quality of their instruction.

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A single clone of Acer saccharinum was selected and propagated from each of 15 provenances across the plant native range. The clones were field grown in Carbondale, Ill., during the study period. Plants were sampled during Winter 1992-93 and 1993-94 and assayed for low-temperature tolerance. During both winters, plants exhibited greatest variation in tolerance around the November and April sampling dates. In midwinter, there was little variation observed and 13 of 15 clones were tolerant to at least -40C. The relationship among Acer saccharinum provenance and cold tolerance curves will be discussed.

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For genetic transformation studies, it is important that efficient adventitious regeneration systems be developed. In previous studies we had stimulated adventitious shoot formation from rhododendron leaf explants. To further determine which explants would be best to inoculate with Agrobacterium, we compared shoot organogenesis from small (2-4 mm long), medium (>4-8 mm long), and large (>8 mm long) leaves excised from in vitro shoot cultures. Across all reps (up to 66 explants), large leaves produced a mean of 23.4, medium produced 6.1, and small produced 2.2 adventitious shoots after 18 weeks. Adventitious microshoots were rooted in preformed peat plugs in high humidity flats. Prior to placement in the plugs, cut ends were treated with various combinations of IBA and NAA. After 8 weeks, control shoots rooted 60% and microshoots treated with 1.25 or 2.50 mM IBA plus 1.25 mM NAA or with a Wood's (1:20 dilution) solution rooted >95%.

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The objective of this study was to investigate the effects of the position on the main stem that large stem segments were harvested from on forcing and subsequent rooting of Betula nigra L. (river birch) softwood shoots. The main trunks of eight adult-phase native trees (four trees per run of the experiment) were cut into 50-cm long segments from the ground up. The segments placed in horizontally in 52 × 25 × 6.5 cm (l × w × h) flats containing perlite and were positioned so the bottom one-third of the stem was within the medium. Shoots were forced under natural photoperiod and intermittent mist. This experiment was conducted twice. Data were collected weekly for fourteen weeks on the number of softwood shoots each segment produced, shoot length, number of rootable shoots (>6 cm long), the length of time that the stem segments produced rootable shoots, and the rootability of these shoots treated with 3000 ppm IBA in talc. The number of harvested shoots was greater in Run 1, with the basal segments producing the most harvestable shoots. However, the upper segments in Run 2 produced the most harvestable shoots. Softwood shoots that rooted were placed under intermittent mist. Out of the 540 harvested shoots for both runs, 82.4% rooted, with the majority of those from Run 1. Shoots harvested from this run began producing roots about 6 weeks after harvest, and continued until the end of the experiment. Run 2 shoots began root initiation about 3 weeks after harvest and ended about 2 weeks before the end of the experiment. Run 1 had an mean of 8.3 roots per shoot and Run 2 had an mean of 6.2 roots. The relationship between juvenility and shoot forcing and subsequent rooting will be discussed.

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Hard-to-root hardwood cuttings of Vitis aestivalis `Norton' were collected during Feb. 1999. Cuttings had three nodes and were 10 to 15 cm long. Prior to treatments, cuttings were submersed in a solution of 9.5 g/1L of ZeroTol (a mixture of hydrogen dioxide and peroxyacetic acid). The bottom two nodes were placed into 1 vermiculite: 1 perlite (by volume) and set under mist in the greenhouse at of 20/15 °C day/night). About 5 weeks after treatment, number of roots and root length data were collected. The bottom 2 cm of cuttings in one experiment received a 30-s dip in 0, 2500, 5000, 7500, or 10,000 mg/L IBA and/or NAA to determine the effects of these treatments on rooting of hardwood cuttings. IBA and NAA are not significantly different, however there was a positive linear relationship between rooting and concentration of auxin. As concentration of auxin increased, mean number of roots increased. In additional experiments, cuttings treated with 0 or 5000 mg/L of IBA were compared based on timing after harvest of cuttings and treatment. Of the cuttings treated and placed under mist on 26 Mar. 1999, 30% of the control cuttings rooted and 50% of the cuttings treated with 5000 mg/L rooted. Two weeks later, 65% and 55% of the cuttings treated with 5000 mg/L rooted respective to the 0- and 5000-mg/L treatments. One week later (14 Apr. 1999), 77.5% and 72.5%, respectively, rooted. This suggests that timing after harvest for placing the cuttings in a propagation bed is important for increasing the rooting percentage of `Norton' hardwood cuttings.

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