SELECTION AGAINST HOMOZYGOTES AND RESOURCE-ALLOCATION IN THE MATING SYSTEM OF EUCALYPTUS-CAMALDULENSIS DEHNH

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.