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RESEARCH ARTICLE
Contents Vol 55(6)

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

Kim N. Hamilton A C , Sarah E. Ashmore A , Rod A. Drew A and Hugh W. Pritchard B
+ Author Affiliations
- Author Affiliations

A Centre for Forestry and Horticultural Research, School of Biomolecular and Physical Sciences, Griffith University, Nathan, Qld 4111, Australia.

B Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, West Sussex RH17 6TN, UK.

C Corresponding author. Email: k.hamilton@griffith.edu.au

Australian Journal of Botany 55(6) 618-627 https://doi.org/10.1071/BT06188
Submitted: 4 September 2006  Accepted: 5 April 2007   Published: 27 September 2007

Abstract

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%).


Acknowledgements

We gratefully thank Malcolm Smith (QPDI) for his assistance and for supplying fruits, and Dr Deb Stenzel (AEMF) for technical training in SEM. Kim Hamilton received part-funding from the Millennium Seed Bank Project, Royal Botanic Gardens, Kew and the IPGRI–ACIAR project, ‘Development of Advanced Technologies for the Conservation of Tropical Fruits’.


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