Eucalyptus tereticornis has a wide natural geographic distribution from Papua New Guinea to South Australia (6º-38º S), therefore, it is expected the existence of important differences among provenances. Although differences in performance among provenances have been reported in several countries, the existing information is insufficient to allow the choice of the most appropriate provenance as a source of seeds for commercial plantations for humid subtropical climates. In order to evaluate the performance of 20 provenances of E. tereticornis in Uruguay and to generate information that contributes to the identification of the best provenances for humid subtropical climates, survival, individual tree volume, stem straightness and forking were assessed at 9-years-old in 4 sites in the center, north and northeast of Uruguay. Significant differences among provenances for all traits and significant provenance by site interaction for survival, individual tree volume and forking were found. No provenance was best in all sites. The Buckenbowra provenance had simultaneously high volume and survival. The absence of a clear regionalization, coupled with a significant provenance-by site interaction, suggests that local evaluation of different provenances is essential to identify appropriate seed sources, both for tree breeding and for use in commercial plantations.

Background: Single-step genomic BLUP (ssGBLUP) has gained increasing interest from forest tree breeders. ssGBLUP combines phenotypic and pedigree data with marker data to enhance the prediction accuracy of estimated breeding values. However, potential errors in determining progeny relationships among open-pollinated species may result in lower accuracy of estimated breeding values. Unknown parent groups (UPG) and metafounders (MF) were developed to address missing pedigrees in a population. This study aimed to incorporate MF into ssGBLUP models to select the best parents for controlled mating and the best progenies for cloning in a tree breeding population of Eucalyptus globulus. Methods: Genetic groups were defined to include base individuals of similar genetic origin. Tree growth was measured as total height (TH) and diameter at breast height (DBH), while disease resistance was assessed through heteroblasty (the transition from juvenile to adult foliage: ADFO). All traits were evaluated at 14 and 21 months. Two genomic multi-trait threshold linear models were fitted, with and without MF. Also, two multi-trait threshold-linear models based on phenotypic and pedigree information (ABLUP) were used to evaluate the increase in accuracy when adding genomic information to the model. To test the quality of models by cross-validation, the linear regression method (LR) was used. Results: The LR statistics indicated that the ssGBLUP models without MF performed better, as the inclusion of MF increased the bias of predictions. The ssGBLUP accuracy for both validations ranged from 0.42 to 0.68. Conclusions: The best model to select parents for controlled matings and individuals for cloning is ssGBLUP without MF.

Eucalyptus globulus Labill. is one of the most important species in the paper industry. Teratosphaeria nubilosa has affected plantations worldwide, infecting young foliage. Genome-wide association studies (GWASs) are essential to identify genomic segments associated with susceptibility to this disease. The inclusion of genomic strategies in breeding programs is key to the sustainability of the species. The aim of this study was to identify genomic regions associated with growth and heteroblasty (change from juvenile to adult foliage: ADFO) in a tree breeding population of E. globulus. Tree growth was measured as total height (TH) and diameter at breast height (DBH). All traits were evaluated at 14 and 21 months. A multi-trait threshold linear model was developed following the single-step genomic selection methodology. Genetic correlations (r_g) and narrow-sense heritability (h²) for all traits were estimated. Windows of 0.2 Mb were used. Only the windows with an estimated variance greater than 1% were considered. The r_g ranged from 0.51 to 0.97. The h² was high for ADFO (0.83–0.84) and lower for HT (0.37) and DBH (0.53). In growth traits, no QTLs were found that explained more than 1% of the variance. However, two genomic regions related to ADFO were identified on chromosomes 3 and 11.

The adoption of genomic selection (GS) in forest tree breeding allows shortening breeding cycles, increasing selection intensity, and improving the accuracy of breeding values, which translate into increased genetic gains. Therefore, the objective of this work was to design a breeding strategy incorporating GS in the Eucalyptus globulus improvement plan of the INIA. Using the single step genomic selection (ssGBLUP) methodology, a multi-trait model of GS was developed considering different ages of evaluation (14 and 21 months), and combination of growth traits (total height and DBH) and heteroblasty (proportion of adult foliage). The model was tested through the predictive capacity (estimated through intra-population cross-validation), the prediction bias (estimated as the regression coefficient between the reference breeding values and those predicted by the model), and the comparison between the rankings of breeding values from the conventional ABLUP and the ssGBLUP (as the proportion of common individuals in the top 10%). The heritabilities in the strict sense for all traits were high, ranging from 0.51 to 0.72. The predictive abilities of the different cross-validations by site and by trait were high, varying from 0.72 to 0.92. The model tends to slightly underestimate DBH and the proportion of adult foliage at some sites and overestimate them at others (bias between 0.88 and 1.19), and overestimate total height in all sites (bias between 0.51 and 0.68). The proportion of common individuals in the top 10% by conventional selection and GS is high for all traits (0.76 - 0.86). These results suggest that the incorporation of GS in the improvement plan of E. globulus would be efficient. It is proposed to include GS in two stages of the breeding cycle: the selection of the best parents for controlled mating, increasing the selection intensity, and the selection of individuals in the nursery, reducing the stage of field evaluation of the selected clones. This strategy will markedly reduce the selection cycle, allowing commercial clones to be obtained in half the time compared to conventional selection.

Genome-wide association studies (GWAS) have provided significant insights into identifying variants associated with complex traits, but they have contributed little to the study of categorical data. The aim of this study was to identify genomic regions associated with quantitative traits (growth) and categorical traits (heteroblasty) in a tree breeding population of Eucalyptus globulus. Tree growth was measured as total height (TH) and diameter at breast height (DBH). Heterobasty was assed as the precocity of change from juvenile to adult foliage (ADFO). All traits were evaluated at 14 and 21 months. A multi-trait threshold-linear model was developed following the single-step genomic selection methodology. Variance components were estimated using Gibbs sampling process. Genetic correlations (r_g) and the narrow sense heritability (h²) for all traits were estimated. Windows of 0.2 Mb were used and their variances were calculated. Only the windows with estimated variance higher than 1% were considered. The r_g ranging from 0.51 to 0.97. The h² were high for ADFO (0.83-0.84), and lower for HT (0.37) and DBH (0.53). In growth traits, no QTL were found that explained more than 1% of the variance. However, two genomic regions were found related with ADFO, in the chromosome 3 and 11.