Heritability of wood density in E. deglupta

In the first experiment, difference in woody tissue density among clones was significant at the 1% level of probability. There was a pronounced clone x temperature interaction effect (significant at the 5% level).

In the second experiment, there was a significant difference (at the 1% level) in woody tissue density among families. An interaction effect of temperature x family was significant at the 5% level of probability.

There was sufficient information available from this pair of experiments to determine the degree of genetic control of wood density in E. deglupta, at least in young plants.

Of important note was the significant (at the 5% level of probability) genotype (vegetatively propagated clones or families of half-sib seedlings) x environment (different day/night temperature regimes) interaction. This indicated a specific difference in environment (temperature) had different effects on different genotypes (clones or families). When these results are extended to where large changes in environment are involved, such as among markedly different habitats or planting locations, the genotype x environment interaction component may considerably influence the average genotypic response and should be regarded as part of the environmental variance. If favourable, this type of variance would be extremely useful in plantation forestry with E. deglupta since a desirable genotype (or preferably several desirable genotypes) for a particular planting area could then be utilised by vegetative propagation by cuttings (“clonal forestry”).

Heritability of wood density in E. deglupta

The theoretical basis and estimation of heritability of wood density is covered in my PhD thesis.36From the first experiment using clonal cuttings described earlier, the resemblance among clones was estimated by partitioning the observed components of variance corresponding to the grouping of plants into clones. Broad sense heritability for woody tissue in the E. deglupta clones grown in the phytotron was found to be 0.68 with a standard error of 0.17.37

36 Chapter 11, pages 197 – 204 In Davidson J 1972 loc. cit. Heritability measures the proportion of phenotype variability that can be attributed to genetic variation and is expressed as a decimal fraction, that is a value between 0 (genes make no contribution at all to phenotypic individual differences) and 1 (genes are the sole reason for phenotypic individual differences). An estimate of heritability is specific to a particular population in a particular environment. The heritability value is not the same as saying that this fraction of an individual phenotype (what one sees in the field) is caused by genetics. Standard errors for the heritability estimates were calculated using a computer program developed by a then PhD student colleague, Ken Eldridge. See: Eldridge K G 1969 Altitudinal variation in Eucalyptus regnans. A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in the Australian National University, Canberra. 37 Broad-sense heritability is the ratio of total genetic variance to total phenotypic variance.