Genotype by environment interaction for growth of Eucalyptus globulus in Australia

This study assessed the genotype by environment (G x E) interaction for diameter growth in 15 Eucalyptus globulus progeny trials in Australia. Single-site analyses revealed significant subrace and family-within-subrace variance in all trials. Across-site subrace ((r) over cap (s)) and family ((r) over cap (f)) correlations were estimated by linear mixed model analyses of pairs of trials. Using a factor analytic structure for subrace and family random terms in a multi-environment mixed model analysis, best linear unbiased predictions of subrace effects were obtained for each trial. These were then averaged for each of four states (Victoria, Tasmania, South Australia and Western Australia) and across all sites. Statistically significant G x E interaction was detected, and weighted means across states for (r) over cap (s) and (r) over cap (f) were 0.73 and 0.76, respectively. Nevertheless, the three subraces from the Otway Ranges were both fast growing and relatively stable in their ranks over all sites. We evaluated the sensitivity of subraces to changing environmental conditions, on the basis of random coefficient models regressing subrace performance on selected trial climatic variables. The results suggested differential susceptibility of subraces to water; light and (to a less extent) temperature stresses during summer. Moreover, using multivariate techniques to visualize and interpret the across-site correlation structure for subrace effects, we could identify site clusters of reduced G x E interaction related to soil water availability and evaporative demand during summer. A revised site-type classification using these factors should allow a better capture of genetic gains from breeding and deployment.