Kim Nicole Hamilton

Conservation technologies for safeguarding and restoring threatened flora: case studies from Eastern Australia

This paper highlights recent advances and improved scientific understanding of conservation technologies through selected case studies on threatened plant species indigenous to Eastern Australia. This includes investigations into seed desiccation, storage responses and cryopreservation in rainforest species, particularly the socio-economically important Australian native Citrus spp., Davidsonia spp. (Davidson’s plum) and Syzygium spp. This work also (1) increases our understanding of ecological correlates of seed desiccation sensitivity for predictive use and (2) improves restoration practice through better understanding of seed storage and germination requirements. The use of in vitro conservation technologies in support of conservation actions for endangered species is outlined in case studies on Wollemia nobilis (Wollemi pine), epiphytic and terrestrial orchid species, and an endangered fern species.

Seed morphology and ultrastructure in Citrus garrawayi (Rutaceae) in relation to germinability

Combinational traits of seed size and seed-coat hardness in Citrus garrawayi (F.M.Bailey) (syn. of Microcitrus garrowayi) were investigated as markers for estimation of seed morphological and physiological maturity. Seed size (length) and coat hardness correlated well with changes in seed coat and embryo morphological development, dry-weight accumulation, decreases in moisture content and a significant increase in germinability. Seed moisture content decreased from 82 ± 1% in immature seeds to 40 ± 1% at seed maturation. The outer integument of immature seeds consisted of thin-walled epidermal fibres from which outgrowths of emerging protrusions were observed. In comparison, mature seed coats were characterised by the thickening of the cell walls of the epidermal fibres from which arose numerous protrusions covered by an extensive mucilage layer. Immature seeds, with incomplete embryo and seed-coat histodiffereniation, had a low mean germination percentage of 4 ± 4%. Premature seeds, with a differentiated embryonic axis, were capable of much higher levels of germination (51 ± 10%) before the attainment of mass maturity. Mature seeds, with the most well differentiated embryonic axis and maximum mean dry weight, had the significantly highest level of germination (88 ± 3%).

Morphological characterization of seeds of three Australian wild Citrus species (Rutaceae): Citrus australasica F. Muell., C. inodora F.M. Bailey and C. garrawayi F.M. Bailey

The comparative morphology of the seeds of three Australian Citrus species, C. australasica C. inodora and C. garrawayi, was studied. Their seed characteristics were broadly similar to those of the cultivated species of the genus, when observed under light and scanning electron microscopy. Citrus garrawayi differed in seed shape (rounded to triangular) and seed coat morphology (i.e., thicker with longer epidermal protrusions) from C. australasica and C. inodora (rounded surface with flat underside in shape). The well-developed minute epidermal protrusions on the seed coat of C. garrawayi were more similar to those in the cultivated species, C. × sinensis and C. × aurantium. In contrast, the surface topography of C. australasica and C. inodora seeds was more like that of the cultivated species, C. × aurantifolia and C. × limon. Seed morphology, especially surface topography, was found to be a useful tool for taxonomic identification in Australian wild citrus.