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Accueil du site → Doctorat → Australie → 1993 → Seed dormancy, germination and ecology of Eremophila (Myoporaceae) in Western Australia

Curtin University of Technology (1993)

Seed dormancy, germination and ecology of Eremophila (Myoporaceae) in Western Australia

Richmond, Guy Stephen

Titre : Seed dormancy, germination and ecology of Eremophila (Myoporaceae) in Western Australia

Auteur : Richmond, Guy Stephen.

Université de soutenance : Curtin University of Technology.

Grade :Doctor of Philosophy PhD s 1993

Eremophila (Myoporaceae) are hardy arid perennial shrubs and small trees which occur throughout Australia. Their diversity is greatest within the Eremaean province of Western Australia. There is increasing interest in this genus for use in rangeland revegetation, minesite rehabilitation and horticultural programs, due to their tolerances to drought, fire, frost, salinity and grazing. They have proved difficult to grow from fruit. Currently propagation is by cuttings. Previous research has suggested the presence of inhibitory substances within the fruit which controls germination but there is no experimental evidence to support this. Eremophila fruit are characteristically indehiscent : the seeds are only released when the surrounding fruit wall decays. Fruits are dry with an exocarp and endocarp. Fruits may contain multiple seeds ranging from 2-16. Seed germination from fruits is variable due to dead, aborted or insect damaged seed or parthenocarpic fruit. Low seed set may be attributed to poor seasons, a decrease in activity of pollinators or potential sterility within the gene pool. Optimum germination of Erernophila maculata seeds under controlled conditions occurs with a day/night temperature regime of 25/7°C (11/13 hrs). Germination of seeds enclosed within fruits is up to 18%, however if the seeds are excised from fruits then it is as high as 98%. Excised seeds may germinate within 5 days of imbibition, with the majority of radicles emerging after 12 days. Seed longevity decreases with increased seed age (i.e. >10 year old seed viability <4%). Eremophila maculata germination is controlled by physical dormancy, due to the hard woody fruit. This may be overcome using a scarification pretreatment of the fruit. A secondary chemical dormancy mechanism exists within the fruit endocarp. Thin Layer Chromatography revealed that the germination inhibitor is not Abscisic Acid. From polyamide chromatography six fractions were generated. Of these, two were found to inhibit the germination of Eremophila maculata seed. Proton Nuclear Magnetic Resonance spectroscopy showed that the inhibitory compound was not an ABA conjugate. However, the presence of water soluble aromatic glycosides is tentatively proposed. Similar germination dormancy processes occur within E. racemosa, a closely related species to E. maculata. Field studies at Mt. Keith (Wiluna) and Mt. Weld stations (Laverton) indicate that Eremophila shows both germination and growth responses after heavy rainfall. Eremophila spectabilis subsp. brevis, at Mt. Keith increased in number from 2,407 adults/ha following a major seedling recruitment event of 15,422 germinants/ha, to 17,829 plants/ha after a one in fifteen year rainfall event. Eremophila germination strategies include multiple germinants (e.g. E. fraseri subsp. galeata producing quintuplet seedlings from one fruit), as well as staggered germination over a 1 year period from the same fruit.

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