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- Author or Editor: John E. Preece x
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.
Abstract
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).
Abstract
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.
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.
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.
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.
A factorial combination of gibberellic acid (GA3) and benzyladenine (BA) was applied in 20% white exterior latex paint to large (40 cm long, >2.5 cm diameter) stem segments of Acer saccharinum L. (silver maple) to determine the effects on forcing new softwood shoots in the greenhouse or laboratory and the subsequent growth of these new shoots in vitro. Stem segments were harvested from 10-year-old field-grown coppice shoots. The GA3/BA-paint mixes were applied to the entire stem segments that were forced in plastic flats filled with 1 perlite: 1 vermiculite (by volume) and watered with care so as not to wet the new softwood shoots. The flats and stem segments were drenched weekly with Zerotol (0.18% H2O2). The softwood shoots were harvested when they were at least 3 cm long. After disinfesting and rinsing, the nodal and shoot tip explants were established aseptically in vitro on DKW medium with no cytokinin or with 10-8M thidiazuron. Coppice shoots were harvested, cut, and painted on 9 Sept., 28 Oct., and 12 Dec. 2005. Although there were no significant differences in shoot production among stem segments painted with various combinations of GA3/BA, stems treated with plant growth regulators produced a mean of 2.7, 1.8, or 0.5 shoots for the three harvest dates compared to 0.5, 0.0, or 0.25 shoots on control stem segments. It is well-known that shoot forcing is poor from September through January; however, use of GA3/BA resulted in growth of dormant epicormic shoots. Shoot tip explants produced the most shoots in vitro after 8 weeks if they were harvested from stem segments treated with 0.03 mM GA3, whereas nodal explants produced the most shoots if harvested from segments that had been treated with 0.01 mM GA3.
Vegetative shoots were forced in the greenhouse from excised stem (branch) sections of dormant Japanese maple (Acer palmatum Thunb.), red maple (Acer rubrum L.), and sugar maple (Acer saccharum Marsh.). Softwood shoots generated in this way were used as stem cuttings in a subsequent adventitious rooting study. Data indicate that maple shoots can be forced using this technique, but that both the percentage of stem sections forming shoots and the number of shoots produced are highly variable among both species and clones. Whereas Japanese and red maple formed shoots on >50% of stem sections, shoots were generated on only 20% of sugar maple stem sections. Significant variability was also observed in rooting response, with red maple shoots rooting at much higher percentages (60%) than either Japanese maple (26%) or sugar maple (15%).
Branches were collected from trees in July. Lengths with a 2.5-cm caliper were cut to 30 cm and placed horizontally into flats of perlite with half of the diameter of each stem above the perlite surface. Flats were watered daily with tap water and stems were kept moist. Buds swelled quickly, and after 6 days, small epicormic shoots were visible. These softwood shoots continued to elongate and retain good turgor for 2 weeks, when they were excised and placed in vitro. Shoottip and nodal explants were placed onto MS medium with 1 μM BA; 1 M IBA; and 0, 3, or 10 μM TDZ where shoots slowly elongated. Forcing large stems in the greenhouse has been superior to forcing smaller stem tips in the laboratory because of lower contamination (40% on shoots from large stems vs. up to 90% on shoots from small stems), longer life of the softwood shoots (less wilting from the larger stems), a longer time during the year for forcing, and the possibility of forcing shoots from more juvenile wood than stem tips.