Outcrossing in interspecific hybrids between Eucalyptus spathulata and E. platypus
M. A. B. Wallwork A B and M. Sedgley A C DA Department of Horticulture, Viticulture and Oenology, The University of Adelaide, Waite Campus, PMB 1, Glen Osmond, SA 5064, Australia.
B Present address: Adelaide Microscopy, The University of Adelaide, Frome Road, Adelaide, SA 5005, Australia.
C Present address: Faculty of The Sciences, University of New England, Armidale, NSW 2351, Australia.
D Corresponding author. Email: margaret.sedgley@une.edu.au
Australian Journal of Botany 53(4) 347-355 https://doi.org/10.1071/BT04081
Submitted: 4 June 2004 Accepted: 1 February 2005 Published: 24 June 2005
Abstract
Outcrossing was investigated in interspecific hybrids between self-fertile Eucalyptus platypus Blakely and partially self-sterile E. spathulata Hook., which shows both pre- and post-zygotic timing. Four hybrid trees were used for the study, two with E. spathulata and two with E. platypus as female parent. Each hybrid had a similar number of locules to each other and to the E. platypus parent, and an intermediate number of ovules per flower compared with the parent species. Controlled hand-pollinations were carried out, in which both self- and cross-pollen from the other hybrid tree with the same female parent species was applied to flowers on each of the four trees, and observations were made 10 days, 4 weeks and 8 weeks after pollination and at seed maturity. In all hybrids, mean seeds per capsule was consistently higher following cross-pollination than following self-pollination. All hybrids showed a reduction in pollen tube number between the top and base of the style when examined by fluorescence microscopy. One tree had significantly fewer cross- than self-pollen tubes at the base of the style, but a similar number of ovules was penetrated by pollen tubes following both treatments. In the other three, there was no difference between cross- and self-pollination in pollen tubes in the style. In three of the four trees there was no difference in ovule penetration following self- or cross-pollination, but in the other, more crossed than selfed ovules were penetrated. Light-microscopy observation of ovules indicated that ovule abortion following fertilisation accounted for the reduced numbers of seeds following self-pollination and to a lesser extent following cross-pollination. All four hybrid trees, irrespective of female parent, were partially self-sterile and resembled the partially self-sterile E. spathulata rather than the self-fertile E. platypus. While the timing of outcrossing control of E. spathulata was both pre- and post-zygotic, only one hybrid was similar, with the other three showing post-zygotic control.
Acknowledgments
The authors acknowledge technical assistance from Jana Kolesik and Anne Lillecrapp. Thanks go to Michelle Lorimer from Biometrics SA for statistical assistance. The research was funded by the Australian Research Council.
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