136 Moore: Root Tip Growth and the Presence of Leaves Affect Epicormic and Lignotuberous Shoot Development damage was clear), and the third group of 10 seed- lings were left intact after treatment. Thermocouples were placed in the ovens to ensure consistent, non-fluctuating temperatures and in the grow- ing media of the containers to record temperatures (Moore 2015). This enabled the temperatures and durations at which E. obliqua seedling root apices were killed to be determined and also made it possible to ensure that in other experiments, container media temperatures did not reach levels that would damage root apices. The death of plant tissue was determined using plant impedance ratios according to the method of Moore (1979), which indicate the impact of a treat- ment on cellular membranes. Killing of plants at 80 and 100 °C was very rapid, and given the limited sup- ply, plants were not sacrificed by heating for the lon- ger durations above 32 and 16 minutes, respectively. The growth of at least 2 root tips per container at the outer surface of the root mass were measured for all control and treated plants using callipers, measuring back from the tip to a small, black, water-insoluble ink mark on the root that did not wash off when seed- lings were irrigated and would not contaminate the growing medium. The mark also allowed the identifi- cation of root tips to be measured from week to week. Figure 1. Diagram showing the specifically designed contain- ers allowing daily root tip inspection to determine whether the root tips were healthy and when selected root tips had resumed growth. Experiment 2 into the pipe and bent inwards to support an inverted cap with drainage holes that formed the base of the container. The base of the container could then be placed over a piston that allowed the content of the container to be pushed upwards for inspection with- out damaging or disturbing the roots growing on the surface (Figure 1). Experiment 1 Groups of 30 seedlings were subjected to a stress treat- ment that involved heating the aboveground parts of the seedlings in Qualtex® ovens (Qualtex, Murarrie, QLD, Australia) at temperatures of 40, 60, 80, and 100 °C for durations of 2, 4, 8, 16, 32, 64, and 128 minutes (Moore 2015). One group of 10 seedlings that had been heat stressed were subjected to immediate decapitation, and another group of 10 seedlings had a delayed decapitation (after 7 days when the extent of ©2021 International Society of Arboriculture Experiment 3 Groups of 7 seedlings were decapitated so that 0, 2, 4, or 8 leaves were left upon the stem of plants to deter- mine whether the number of intact leaves left on a plant had an effect on shoot production and survival. The decision to leave different numbers of leaves was based on experiments 1 and 2, which showed that for seedlings heat treated at 60 and 80 °C for longer dura- tions, all leaves were killed, but for milder treatments, Seedlings were treated in “parallel” decapitations, where similar proportions of the stem and leaves to those killed by heat treatment were removed. The degree of killing of seedling leaf and stem tissues was deter- mined using the methods of Moore (2015). In these experiments, seedlings simulating 100 °C for 2 min- utes, 80 °C for 8 minutes, and 60 °C for 32 minutes were decapitated 20 mm above the potting medium (Figure 2). The 80 °C 2-minute and 4-minute simula- tions were decapitated 120 mm and 80 mm above the soil medium, and for the 60 °C 2-, 4-, 8-, and 16-minute simulations, seedlings were decapitated 20 mm, 40 mm, 80 mm, and 120 mm from the shoot apex (Figure 2).
July 2021
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
