Preferential outcrossing in Banksia ilicifolia (Proteaceae)
Bambang Heliyanto A C , Erik J. Veneklaas A , Hans Lambers A and Siegfried L. Krauss A BA School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
B Botanic Gardens and Parks Authority, Kings Park and Botanic Garden, West Perth, WA 6005, Australia.
C Corresponding author. Email: bheliyan@agric.uwa.edu.au
Australian Journal of Botany 53(2) 163-170 https://doi.org/10.1071/BT04011
Submitted: 27 January 2004 Accepted: 9 September 2004 Published: 31 March 2005
Abstract
The breeding system of Banksia ilicifolia was assessed by performing controlled hand-pollination manipulations on flowers in a natural population in Perth, Western Australia. The percentage of 2000 flowers per treatment converted to fruits and seeds was assessed across 24 recipient plants following (1) self-pollination, (2) local outcross pollination (same population), (3) non-local outcross pollination (pollen sourced from another population 30 km away), (4) unpollinated but bagged flowers and (5) unpollinated, unbagged flowers (natural pollination). The relative performance of the resulting seeds was assessed by seed weight, germination rates and, in an unplanned component of the study, resistance to a fungal pathogen. The percentage of flowers converted to fruits following self-pollination was low (0.9%), but demonstrated self-compatibility. Fruit set following cross-pollinations (3.6 and 3.3% for non-local and local crosses, respectively) was significantly greater than that following self-pollination, open-pollination (0.4%) and autogamous (0.04%) treatments. Low fruit set for open-pollinated flowers, compared with self- and outcross-pollination treatments, suggests pollen limitation. Pollen tubes were observed in 15 and 20% of upper styles of flowers hand-pollinated with self and local outcross pollen, respectively. Seed germination was dependent on the source of pollen, where fewer selfed seeds germinated (37%) than did both non-local and local outcrossed seeds (83 and 91%, respectively). Selfed seedlings showed poorer survival (33.3%) following fungal attack than both non-local and local outcrossed seeds (69.2 and 68.5%, respectively). Only 13% of selfed seeds survived to be 2-month-old seedlings, compared with 63% for non-local and 57% for local outcrossed seeds. Ultimately, for 2000 flowers hand-pollinated with self pollen, only three seedlings survived to an age of 16 weeks, compared with 37 and 45 seedlings for local-cross and non-local cross treatments on 2000 hand-pollinated flowers, respectively. These results indicate that in this population, B. ilicifolia is self-compatible, but preferentially outcrossing, with strong early acting inbreeding depression. Consequently, the breeding system of B. ilicifolia promotes the maintenance of genetic variation and a high genetic load.
Acknowledgments
We thank Dr Jamie O’Shea and Bob Cooper, for permission to work in the Harry Warring Marsupial Reserve. Bambang Heliyanto thanks Ausaid for providing the scholarship to undertake postgraduate research at the University of Western Australia. Professor J. Kuo and Staff of the Centre for Microscopy and Microanalysis are acknowledged for their help with microscopy technique. We thank Kevin Murray for statistical advice, Titiek Yulianti for identifying the fungal type of disease in the germination and seedling stage, and Ross Goldingay and two anonymous reviewers for helpful comments that improved an earlier draft of this paper.
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