Date Published: October 12, 2018
Publisher: Public Library of Science
Author(s): Yongjun Li, Heidi S. Dungey, Mike Carson, Sue Carson, Daniel Doucet.
Twenty-eight clonal trials of radiata pine planted across Australia and New Zealand were used to investigate genetic variation and genotype by environment (G×E) interaction for diameter-at-breast-height (DBH), height and Dothistroma resistance (DO_R). The average narrow-sense heritabilities were 0.11, 0.21 and 0.30 while the average broad-sense heritabilities were 0.27, 0.34 and 0.40 for DBH, height and Dothistroma resistance, respectively. Dothistroma resistance was assessed as the percentage of needles that were not affected by Dothistroma needle blight. G×E interactions were analysed using an approximate reduced factor analytic model. Apparent G×E interactions were estimated for DBH, height and Dothistroma resistance. Estimates of G×E interactions and their standard errors were strongly influenced by the level of connectivity between trials, in terms of common clones and common parents. When there was sufficient connectivity between trials (more than 30% common clones between trials), a high level of G×E interaction was found for DBH and height but not for Dothistroma resistance. In two simulated clonal trials planted in two environments, low connectivity between environments resulted in a lower estimated genetic correlation between environments with an increased standard error. These results suggest that the number of clones in common between clonal trials is a key factor for inclusion in future experimental designs for estimating G×E interaction. When designing clonal trials for use in multiple environments for accurately estimating the level of G×E, if the resource for creating connectivity between environments is limited, at least 30% of the clones need to be in common between environments.
Radiata pine (Pinus radiata) is a fast-growing pine species, native to the Central Coast of California and both Guadalupe Island and Cedros Island of Mexico . Its timber is used for paper making, reconstituted board products and plywood manufacture, house construction and furniture making . There are over four million ha of planted radiata pine worldwide, with New Zealand (1.72 million ha) and Australia (0.77 million ha) among the countries with plantations . Radiata pine plantations in Australia are in the southern part of the country, distributed in New South Wales, Victoria, South Australia, Tasmania and Western Australia. In New Zealand, the species is planted across the country, with 70% in the North Island and 30% in the South Island . The New Zealand forest industry has a vision to significantly improve forest profitability by doubling productivity on a per hectare basis by 2025 while also improving wood quality and increasing resistance to pests and diseases . Current breeding stock will need to be improved genetically in order to achieve this increased productivity target.
This study has shown that the precise estimation of genetic correlations between trials depends on the levels of connectivity between trials. Apiolaza  found an association between the number of parents in common across trials and the magnitude of the standard error of the estimated genetic correlation, and that the estimated correlation tended to be under-estimated when there were fewer parents in common. In the current study with clonal trials, the number of parents was 17–30 with an average of 21. The percentage of parents in common was 47–100% with an average of 78%. The connectivity between trials via parents was, therefore at a reasonable level. However, it should be noted that the trials in this study were not designed to screen parents but rather to screen the individual clones. Despite this complication, the current study clearly showed that there was a positive association between the number of clones in common across trials and the size of the estimates of genetic correlations between trials. Fig 3 showed a trend for the estimated correlation tending to be lower when the percentage of clones in common between trials was low, which means that the genetic correlations might be not reliable in these cases. Apiolaza (28) also reported that any pair of trials with less than 20 parents in common (either directly or via previous generations in the pedigree) caused convergence problems in obtaining estimates of genetic correlation. The current study also expressed convergence problems in estimating pairwise genetic correlations when the number of clones in common was low.