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Sources of variation in self-incompatibility in the Australian forest tree, Eucalyptus globulus

McGowen, MH, Vaillancourt, RE, Pilbeam, D and Potts, BM 2010 , 'Sources of variation in self-incompatibility in the Australian forest tree, Eucalyptus globulus' , Annals of Botany, vol. 105, no. 5 , pp. 737-745 , doi:

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† Background and Aims One of the major factors affecting the outcrossing rate in Eucalyptus globulus is thought
to be the inherent self-incompatibility (SI) level of the female tree. SI in this species is mainly due to late-acting
pre- and post-zygotic mechanisms operating in the ovary, and not S alleles. This study aimed to assess the phenotypic
variation in SI levels within E. globulus and determine its genetic control and stability across pollination
techniques, sites and seasons.
† Methods SI levels were estimated for 105 genotypes originating from across the geographical range of
E. globulus over multiple years of crossing. Separate grafted trees of some genotypes growing at the same
and different sites allowed the genetic basis of the variation in SI to be tested and its stability across sites and
seasons to be determined. The SI level of a tree was measured as the relative reduction in seeds obtained per
flower pollinated following selfing compared with outcross pollinations. Thus, if seed set is the same, SI is
0 %, and if no self seed is set, SI is 100 %.
† Key Results The average SI in E. globulus was 91% and genotypes ranged from 8 to 100% SI. Most genotypes
(.75 %) had SI levels .90 %. There were highly significant differences between genotypes and the within-site
broad-sense heritability of percentage SI was high (H2 ¼ 0.80+0.13). However, there was evidence that growing
site, and to a lesser extent season, can affect the expression of SI levels. Trees with low reproductive loads produced
relatively more seed from selfed flowers.
†Conclusions There is a strong genetic basis to the phenotypic variation in SI in E. globulus within a site.
However, the level of SI was affected, but to a lesser extent, by the environment, which in part may reflect
the higher probability of selfed zygotes surviving on sites or in seasons where competition for resources is less.

Item Type: Article
Authors/Creators:McGowen, MH and Vaillancourt, RE and Pilbeam, D and Potts, BM
Keywords: Heritability, plasticity, resource allocation, SI, mating systems, forest tree.
Journal or Publication Title: Annals of Botany
ISSN: 0305-7364
DOI / ID Number:
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Copyright © 2010 Oxford University Press

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