Sh. James et Wj. Kennington, SELECTION AGAINST HOMOZYGOTES AND RESOURCE-ALLOCATION IN THE MATING SYSTEM OF EUCALYPTUS-CAMALDULENSIS DEHNH, Australian Journal of Botany, 41(3), 1993, pp. 381-391
Allozyme genotypes of seed progeny were determined for an essentially
self-pollinating individual of E. camaldulensis heterozygous at the LA
P and GPI-2 loci. The seed exhibited a normal 1:1 allelic recovery, an
d an excess of heterozygotes relative to Mendelian expectations that w
as significant at the GPI-2 locus (chi2[1] = 58.0, P<0.001). GPI-2 all
ozyme genotypes were also determined for the seed produced by an open-
pollinated E. camaldulensis growing in a mixed clonal plantation. Most
of the seed produced by this plant exhibited non-maternal alleles and
was the result of cross-pollination. We conclude that post-zygotic se
ed selection was selectively eliminating genetic homozygotes from the
selfed progeny and amplifying the frequency of cross-pollination produ
cts in the open-pollinated tree. We also found that the level of selec
tion within fruits of the self pollinated tree was dependent upon the
number of seeds and the number of ovules per capsule (P=0.019, r2=0.63
and P=0.008, r2=0.79 respectively using pooled classed data); selecti
on intensities were found to be greater in fruits containing lower num
bers of seeds or ovules. This may reflect the level of resources alloc
ated to the fruit by a hormonally controlled positive feedback system.
Incorporating the notions of heterosis or selection against recessive
homozygotes and resource allocation allowed the presentation of alter
native explanations for the low estimates of t found in eucalyptus pro
ducing low numbers of flowers and for the temporal heterogeneity in ou
tcrossing rates reported in E. delegatensis.