Genotype by environment interaction of Pinus radiata in New Zealand
In New Zealand, a formal tree improvement and breeding programme for Pinus radiata (D.Don) commenced in 1952. A countrywide series of progeny trials was progressively established on over sixty sites, and is managed by the Radiata Pine Breeding Company. Diameter at breast height data from the series was used to investigate genotype by environment interaction with a view to establishing the need for partitioning breeding and deployment efforts for P. radiata. More than 280,000 measurements made this study one of the largest for genotype by environment interaction ever done. Bivariate analyses were conducted between all pairs of sites to determine genetic correlations between sites. This enabled construction of a proximity matrix by subtracting each correlation from unity. The process of constructing the matrix highlighted issues of connectedness between sites. Multiple regression on resemblance matrices was carried out by regressing a number of environmental correlation matrices on the diameter at breast height correlation matrix. Genotype by environment interactions were found to be driven by total rainfall and extreme maximum and minimum temperatures. In addition, a method from Graph Theory using proximity thresholds was utilised as a form of clustering. However, in this study, minimal grouping of sites was observed. Future work, incorporating ASReml to conduct the univariate and bivariate analyses, is expected to produce clearer results than experienced in this pilot study.