(172) The Influence of Environment, Media, and Zerotol on Forcing and In Vitro Establishment of Softwood Shoots from Large Stem Segments of Acer saccharinum and Fraxinus pennsylvanica

The objectives of this research were to study the effects of three environments (lab, mist, or fog), four media treatments [perlite, vermiculte, 1 perlite: 1 vermiculite (by volume), or a control (empty flats)] and zerotol treatments on shoot forcing and subsequent transfer of explants to in vitro conditions. Stem segments from field-grown trees were cut to 40-cm lengths before being placed in flats with the media treatments. Half of the flats under mist and fog were drenched weekly with zerotol (0.18% H2O2). In a separate study, silver maple was forced under mist and drenched weekly with zerotol at 0%, 0.09%, 0.108%, 0.135%, 0.18%, 0.27%, or 0.54% H2O2. Shoots (≥5 cm) were harvested and nodal and shoot tip explants were surface disinfested and placed in vitro on DKW medium with 10-8 M thidiazuron plus 1.0 μM indolebutyric acid. Species did not interact with environment, media, or zerotol treatment, and silver maple produced a mean of 6 shoots per stem segment, while green ash produced a mean of 1.2 shoots. There was a significant interaction among perlite, vermiculite and environment, with the most shoots (6.7/stem segment) produced under mist in the perlite: vermiculite mix. Silver maple explants from the lab had only 4% microbial contamination, whereas 68% of explants from fog and 92.2% of explants from mist were contaminated. When forcing was under fog, in perlite, and drenched with zerotol, explants had a 43% rate of contamination. In a separate study, when silver maple stems were placed under mist and drenched weekly with 0.18% H2O2, 46% (18 of 39 explants) established cleanly in vitro. Contamination was higher with misted explants that were drenched with higher or lower concentrations of zerotol.

The Influence of Location of Main Stem Segment Origin on Forcing and Rooting of Softwood Shoots of Betula nigra L.

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.

Comparison of Chilling Requirement in `Ta Tao' Budded Peach Trees by Shoot Forcing

Peach trees exposed to `Ta Tao' vegetative chip bud grafts have been shown to have physiological changes that include bloom delay, delayed maturity, reduced shoot vigor, and early autumn defoliation. `Ta Tao' is known to be infected with the graft transmissible agent Peach Latent Mosaic Viroid (PLMVd). PLMVd has been associated with bloom delay and reduced shoot vigor. `Coronet' peach trees planted in a high-density, Y-trained orchard system were treated with vegetative chip buds from `Ta Tao'. Transmission of PLMVd was confirmed in the treated trees by cRNA probe hybridization. A shoot forcing study was set up to determine if exposure to `Ta Tao' would alter the chilling requirement of `Coronet' peach. Terminal fruiting shoots were collected periodically during the dormant season from 8 Jan. 1999 to 19 Feb. 1999, which represented a range of chill hour accumulation from 574 to 927, respectively. Shoots were forced in a greenhouse, and chilling requirement was considered complete when 50% of the flowers opened. Chilling requirement was not changed by exposure to `Ta Tao' chip buds. The number of days required for shoots to bloom was significantly and consistently longer for the `Ta Tao' treated trees. The number of shoots responding to forcing conditions was significantly less in the treated trees. The data suggest that the graft transmissible effects from `Ta Tao' buds increased the growing degree hours required for `Coronet' leaf and flower bud emergence after rest completion under greenhouse forcing conditions.

Epicormic Shoot Forcing of Adult Red Maple, Sugar Maple, and Eastern Black Walnut

Dormant stem sections from three individuals each of Acer rubrum (red maple) and A. saccharium (sugar maple), and three clones of Juglans nigra (eastern black walnut) were collected from lower lateral branches of trees at least 30 years old. The stem sections were cut into 50-cm-long segments and placed horizontally in soilless media in a greenhouse. Two experiments were conducted to determine which treatments were most efficient for the production and elongation of epicormic shoots from latent buds below the bark. The first experiment consisted of a factorial arrangement of two levels of shading (not shaded or covered with 48% Saran shade cloth) and two levels of flooding (not flooded or flooded to a depth of 1/3 to 1/2 the diameter of the stem sections). Flooded treatments contained 0.025% NaClO to control microbial growth. The second experiment consisted of three media treatments: perlite, vermiculite, or a 1 perlite: 1 vermiculite (by volume) medium. No stem segments of any species in flooded treatments produced softwood shoots. Neither shading nor media treatments affected shoot number or length for any of the species. Additional sugar maple segments collected after budbreak produced more and longer shoots than those collected while dormant.