Factors affecting variation in outcrossing rate in Eucalyptus globulus
Briony Patterson A , René E. Vaillancourt A , David J. Pilbeam B and Brad M. Potts A CA School of Plant Science and Cooperative Research Centre for Sustainable Production Forestry, University of Tasmania, Private Bag 55, Hobart, Tas. 7001, Australia.
B Southern Tree Breeding Association Inc., 2 Eleanor Street, PO Box 1811, Mt Gambier, SA 5290, Australia.
C Corresponding author. Email: B.M.Potts@utas.edu.au
Australian Journal of Botany 52(6) 773-780 https://doi.org/10.1071/BT03186
Submitted: 22 December 2003 Accepted: 14 October 2004 Published: 24 December 2004
Abstract
The mating system of the animal-pollinated forest tree species Eucalyptus globulus Labill. was investigated in a clonal seed orchard to determine the importance of self-incompatibility, floral timing, floral abundance and canopy position on explaining variation in outcrossing rates. Outcrossing rates were highly and significantly correlated with the degree of self-incompatibility of individual genotypes (R2 = 0.92). Outcrossing rates were also significantly higher in the upper than in the lower parts of tree canopies (0.78 ± 0.1 and 0.54 ± 0.1, respectively). In contrast, neither flowering time nor abundance of flowers on individual trees revealed consistent effects upon outcrossing rates, suggesting that these factors are either less important or inherently more unpredictable because their effects partly depend on complex interactions with animal pollinators. Screening seed orchards in order to identify trees with high self-incompatibility and restricting seed collection to these trees will ensure that a high proportion of the seed used for plantations is derived from outcrossing, thereby minimising the deleterious effects of inbreeding depression.
Acknowledgments
We thank Gillian Beattie for technical assistance, Paris Ewart and WACAP Tree Farms Pty Ltd for providing seed, flowering data, SI measurements as well as the ARC for funding a SPIRT grant together with the STBA, Gunns Ltd, Silvagene Pty Ltd and WACAP.
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