Optimising deployment of Pinus radiata : an evaluation of methods for the propagation of cuttings and the estimation of genetic parameters to quantify gains from deploying with stecklings

This thesis investigates current and potential deployment strategies using stecldings of Pinus radiata. The investigations showed that the growth of stecldings at 9 months of age was influenced by the age of the stock plant from which they were propagated, the genotype, an interaction between these two effects, and stock plant source. Stock plants raised from seed showed the fastest growth rates and produced cuttings that also showed the fastest growth rates. Growth of stecldings declined with increasing stock plant age (2 to 5 years). It was also shown for most traits that estimates of genetic variance and heritabilities were similar for seedlings and stecldings propagated from 2 year-old stock plants, with very high genetic correlations between these propagule types. However inflated estimates of genetic variance and heritability were found for two out of three traits measured in stecklings propagated from 6 year-old stock plants. This was attributed to either dominance effects or propagation effects common to a fullsib family, C-effects. Also poor correspondence between the performances of seedlings and stecklings propagated from 6 year-old stock plants was found for one trait.Deployment of families as stecklings based on the performances of seedlings is viable for cuttings that come from young stock plants (up to 2 years of age). By comparison, the use of stecklings from older stock plants may bias the estimates of genetic merit in P. radiata and result in yields which differ from those expected from breeding programs. Age-age correlations were highest when comparing traits measured at later ages, between 6 and 11 years of age, rather than between 9 months and 6 years of age and 9 months and 11 years of age. It could not be shown whether selection of superior families can be carried out at an earlier age than is currently employed. The study also indicates that the deployment strategy for P. radiata which will provide the grower the highest potential economic benefit is clonal forestry. Two modelled scenarios predicted genetic gains of a clonal forestry deployment strategy to be at least 50 % greater than a family forestry deployment strategy.