Effect of boiling water, seed coat structure and provenance on the germination of Acacia melanoxylon seeds
Geoffrey E. Burrows A D , James M. Virgona B and Roger D. Heady CA Institute for Land, Water and Society, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
B EH Graham Centre for Agricultural Innovation, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
C Fenner School of Environment and Society, The Australian National University, Canberra, ACT 0200, Australia.
D Corresponding author. Email: gburrows@csu.edu.au
Australian Journal of Botany 57(2) 139-147 https://doi.org/10.1071/BT08194
Submitted: 23 October 2008 Accepted: 12 March 2009 Published: 11 May 2009
Abstract
Acacia melanoxylon (Mimosoideae or Mimosaceae) is a high quality timber tree with an extensive natural distribution in Australia and a wide genetic and phenotypic diversity. Seeds from three widely differing provenances in Tasmania were tested to determine whether they had different responses to various dormancy-breaking treatments. All provenances had limited germination (<11%) if seeds were untreated and between 85% and 91% germination after 40 days if the seeds were nicked. For all provenances short (≤60 s) exposure to boiling water gave high germination percentages. These values were generally lower, although usually not significantly so, than the germination percentages following nicking. Germination percentages decreased with increasing time of exposure to boiling water, although one provenance had a significantly greater tolerance to one of the longer (20 min) treatments. Nicked seeds germinated quickly and uniformly, whereas those subjected to the boiling-water treatments germinated after a longer period and more gradually. In untreated seeds, the lens was a low, elliptically shaped dome (~110–135 µm wide, 140–190 µm long). In more than 99% of the seeds examined, the structure of the lens was markedly altered after a 10-s exposure to boiling water. A wide diversity of altered lens structure was found, from a circular hole between the macrosclereids, to a short fissure where the macrosclereids did not separate to their bases. Nicked seeds had a 200–375 times greater area for water uptake than a fully disrupted lens and this was probably the principal reason why the nicked seeds germinated sooner and more rapidly.
Acknowledgements
We thank Warwick Grant for assembling the materials needed for the germination trials. We thank the Electron Microscope Unit of the Australian National University for access to SEM facilities. We thank horticulture students at CSU for assistance in establishing some of the experiments.
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