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The seed ecology of Lebeckia ambigua

Edwards, Thomas (2015) The seed ecology of Lebeckia ambigua. Honours thesis, Murdoch University.

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Lebeckia ambigua is a perennial legume native to the heathlands of the Fynbos biome in the Western Cape region of South Africa. The species has been identified as a potential agricultural cultivar for the south west of Western Australia, where the edaphic conditions are similar and equally challenging. The species is very fecund and the seed produced has a very high percentage of hard seed dormancy (88-99%). This seed ecology needs to be understood in the domestication of the species.

Successful integration of L. ambigua into any agricultural system will require an understanding of the species-specific nature of its hard seed dormancy, and the environmental and artificially imposed triggers required to break it. This will ensure that enough seed germinates to successfully establish the legume in new sowings. This was the main focus of the research presented here.

A germination level of 68% of the seed was achieved in response to optimisation of a physical scarification method. Further, L. ambigua seeds displayed a high tolerance to applications of moist heat, and thus the best overall germination (73%) was encountered in response to simulated fire experiments.

However when L. ambigua seeds were left in the field, exposed to normal environmental conditions, less then 10% of seed softened to become germinable in the first winter (24 weeks of exposure), and only an additional 30% had softened by the following winter (57 weeks of exposure). Seed was originally collected from geographically separated and discrete populations of L. ambigua in South Africa.

Substantial variation was also detected in the occurrence and breakdown of hard seed between provenances. This provides an opportunity for further selection of desired seed traits during the domestication of the species.

These results are quite unique when set against the most common perennial legumes currently utilised in agriculture. Instead the hard seed dynamics discovered in L. ambigua are more comparable to the annual legumes used in ley farming systems. This potentially provides an opportunity to integrate a perennial legume phase in a uniquely flexible way, by exploiting the hard seed traits of the new legume. It may be possible to regenerate stands from hard seed banks in the same way as applied in conventional annual ley farming systems, and this would be revolutionary when applied to a perennial species.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Howieson, John and Nutt, Brad
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