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Browsing School of Agricultural, Earth and Environmental Sciences by Subject "Acacia mearnsii--Research--South Africa."

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    Estimating leaf area index (LAI) of black wattle (Acacia mearnsii) using Landsat ETM+ satellite imagery.
    (2003) Ghebremicael, Selamawit T.; Ahmed, Fethi B.
    Leaf area index (LAI) is an important variable in models that attempt to simulate carbon, nutrient, water and energy fluxes for forest ecosystems. LAI can be measured either directly (destructive sampling) or by using indirect techniques that involve estimation of LAI from light penetration through canopies. Destructive sampling techniques are laborious, expensive and can only be carried out for small plots. Although indirect techniques are non-destructive and less time consuming, they assume a random foliage distribution that rarely occurs in nature. Thus a technique is required that would allow for rapid estimation of LAI at the stand level. A means of getting this information is via remotely sensed measurements of reflected energy with an airborne or satellite-based sensor. Such information on an important plant species such as Acacia mearnsii (Black Wattle) is vital as it provides an insight into its water use. Landsat ETM+ images covering four study sites In KwaZulu-Natal midlands encompassing pure stands of Acacia mearnsii were processed to obtain four types of vegetation indices (VIs). The indices included: normalized difference vegetation index (NDVI), ratio vegetation index (RVI), transformed vegetation index (TVI) and vegetation index 3 (VB). Ground based measurements of LAI were made using destructive sampling (actual LAI) and LAI-2000 optical instrument, (plant area index, PAl). Specific leafarea (SLA) and leaf area (LA) were measured in the field for the entire sample stands to estimate their LAI values. The relationships between the various VIs and SLA, actual LAI and PAl values measured by LAI-2000 were evaluated using correlation and regression statistical analyses. Results showed that the overall mean SLA value of Acacia mearnsii was 8.28 m2kg-1 SLA showed strong correlations with NDVI (r=0.71, p
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    Shoot apex culture of Acacia mearnsii (De wild)
    (2007) Thompson, Iain Mungo.; Laing, Mark Delmege.
    Research into the micropropagation of black wattle in South Africa is important for two reasons. Firstly micropropagation technology allows breeders to select and propagate mature tissue, which in turn allows them to better capture selected traits. Secondly, tissue culture may control the highly invasive nature of black wattle. If triploid black wattle can be developed, foresters will then have to rely on clonal propagation to supply material for their growing operations. This research was part of the Institute for Commercial Forestry’s Acacia mearnsii vegetative propagation programme. The main focus of this research was to overcome various problems associated with direct organogenesis of ex vitro material. The shoot apex region was used as the explant in all studies because this region is thought to harbour relatively few internal microbial contaminants and is of sufficient size to withstand stresses associated with micropropagation. The initial research was focussed on the screening of sterilants, searching for a viable alternative to mercuric chloride. Surface sterilisation is integral to any micropropagation technique. This process should do the least amount of plant damage, whilst reducing microbial contamination to an acceptable level. Explants were cultured on Murashige and Skoog (MS) medium supplemented with 2.0 mg L-1 BA and monitored for signs of contamination and shooting. Household bleach proved an excellent alternative to mercuric chloride because it did significantly less damage to the explants than mercuric chloride and is handled easily. There was no significant effect of sterilant exposure time on explant decontamination levels, whilst the shortest exposure time resulted in significantly higher levels of shoot development than the other two times tested. The results of this initial research was developed into a protocol and utilised in subsequent investigations. Due to a considerable variation in the success of the developed surface sterilisation protocol according to different times of the year, a further investigation into the effects of season and mother plant material on shoot apex culture of Acacia mearnsii was undertaken. The success of any tissue culture technique depends on a large array of ex vitro and in vitro variables. The objective of this research was to determine the ii effect of two ex vitro variables, season and mother plant, on shoot apex culture of Acacia mearnsii. Explants from individual mother plants were cultured on MS medium supplemented with 2.0 mg L-1 BA during four separate seasons and monitored for signs of contamination and shooting. Spring was found to be the best harvesting season because spring explants showed significantly higher decontaminated explant levels and shooting levels than explants harvested in the other three seasons. The effect of mother plant selection on the performance of Acacia mearnsii explants during shoot apex culture was also found to be significant, especially with regard to shooting levels. Finally factors influencing shoot elongation of A. mearnsii during shoot apex culture were investigated. In the past, induction of shoot elongation during micropropagation of A. mearnsii was attained through the addition of plant growth regulators and other supplements to the basal culture medium. However, some micropropagation methods in other species have utilised red light as a means of promoting shoot elongation. The objective of this study was to test the effects of an alternative basal medium, red light and differing concentrations of chemical additions to the culture medium on shoot elongation of Acacia mearnsii during shoot apex culture. Four independent experiments were undertaken comparing: shoot elongation on Woody Plant Medium (WPM) to the MS basal medium control; shoot elongation under a red cellophane box compared to control culture light conditions; shoot elongation on media supplemented with various concentrations of GA3 to the un-supplemented control and shoot elongation on media supplemented with combinations of BA and IBA compared to a control. Although no significant effects were observed, many trends were noted. The results indicated that there was no advantage to using WPM instead of MS medium when attempting to elongate shoots, rejuvenated through shoot apex culture of A. mearnsii, whilst the effect of GA3 showed a negative trend. The effects of red light and some BA and IBA combinations showed positive trends on the elongation of initiated shoots. This research successfully addressed some of the problems associated with micropropagation of A. mearnsii. Shoot apex culture shows promise and further research into this technique should be considered. A viable surface sterilant alternative to mercuric chloride was successfully identified. This alternative is not only iii safer to use but shows a large reduction in phytotoxic effects. The effects of season and mother plant on shoot apex culture was successfully investigated, resulting in a better understanding of mother plant influences on tissue culture as well as the identification of an optimum season for explant selection. Finally two possible shoot elongation promoters were identified for further research and a more affordable alternative to red light sources and screens was identified.