Summary• Genomic selection (GS) is expected to cause a paradigm shift in tree breeding by improving its speed and efficiency. By fitting all the genome-wide markers concurrently, GS can capture most of the 'missing heritability' of complex traits that quantitative trait locus (QTL) and association mapping classically fail to explain. Experimental support of GS is now required.• The effectiveness of GS was assessed in two unrelated Eucalyptus breeding populations with contrasting effective population sizes (N e = 11 and 51) genotyped with > 3000 DArT markers. Prediction models were developed for tree circumference and height growth, wood specific gravity and pulp yield using random regression best linear unbiased predictor (BLUP).• Accuracies of GS varied between 0.55 and 0.88, matching the accuracies achieved by conventional phenotypic selection. Substantial proportions (74-97%) of trait heritability were captured by fitting all genome-wide markers simultaneously. Genomic regions explaining trait variation largely coincided between populations, although GS models predicted poorly across populations, likely as a result of variable patterns of linkage disequilibrium, inconsistent allelic effects and genotype · environment interaction.• GS brings a new perspective to the understanding of quantitative trait variation in forest trees and provides a revolutionary tool for applied tree improvement. Nevertheless population-specific predictive models will likely drive the initial applications of GS in forest tree breeding.
Summary
Genome‐wide association studies (GWAS) in plants typically suffer from limited statistical power. An alternative to the logistical and cost challenge of increasing sample sizes is to gain power by meta‐analysis using information from independent studies.
We carried out GWAS for growth traits with six single‐marker models and regional heritability mapping (RHM) in four Eucalyptus breeding populations independently and by Joint‐GWAS, using gene and segment‐based models, with data for 3373 individuals genotyped with a communal EUChip60KSNP platform.
While single‐single nucleotide polymorphism (SNP) GWAS hardly detected significant associations at high‐stringency in each population, gene‐based Joint‐GWAS revealed nine genes significantly associated with tree height. Associations detected using single‐SNP GWAS, RHM and Joint‐GWAS set‐based models explained on average 3–20% of the phenotypic variance. Whole‐genome regression, conversely, captured 64–89% of the pedigree‐based heritability in all populations. Several associations independently detected for the same SNPs in different populations provided unprecedented GWAS validation results in forest trees. Rare and common associations were discovered in eight genes involved in cell wall biosynthesis and lignification.
With the increasing adoption of genomic prediction of complex phenotypes using shared SNPs and much larger tree breeding populations, Joint‐GWAS approaches should provide increasing power to pinpoint discrete associations potentially useful toward tree breeding and molecular applications.
This paper reports the effects of three cycles of reciprocal recurrent selection (RRS) on the means, genetic variances, and on the genetic correlations for several traits in the IG-1 and IG-2 maize (Zea mays L.) populations. Interpopulation full-sib progenies from cycle zero (C 0 ) and from cycle 3 (C 3 ) of RRS were evaluated in two locations. RRS was highly effective to improve the traits according the objectives of the program: grain yield and prolificacy increased significantly, while plant height, ear height, and ear placement decreased significantly. Genetic variances for all traits decreased significantly from C 0 to C 3 , but the genetic correlations did not change consistently across the cycles of selection. The expected responses to the fourth cycle of RRS and the probability of selecting double-crosses from C 3 that outperform those from C 0 showed that the decreases in the genetic variances were not great enough to limit the continued improvement of the populations as well as the use of the improved populations as sources of inbred lines to develop commercial hybrids. However, if the magnitudes of the genetic variances continue to decrease, new sources of improved germplasm should be incorporated into both populations to allow the continued improvement of the interpopulation by RRS.
por proporcionar conhecer pessoas empenhadas em contribuir para a Ciência, pelas amizades construídas durante o período de convivência em Piracicaba, e aos violeiros e cantadores da terra do Rio de Piracicaba. Gostaria de agradecer também a: À Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ), particularmente ao Departamento de Genética, por possibilitar a realização deste trabalho. Ao Conselho Nacional de Desenvolvimento Científico e Tecnológico -CNPq, pela concessão da bolsa de estudo. Ao Prof. Dr. Magno A. P. Ramalho pelo incentivo na realização deste trabalho e indicação desta escola. Ao Prof. Dr. Cláudio Lopes de Souza Júnior, pela orientação, ensinamentos, confiança, paciência e amizade. A Profa. Anete Pereira de Souza e toda equipe do laboratório CEBMEG da Unicamp pela realização das análises laboratoriais.Aos professores do Departamento de Genética pelos ensinamentos transmitidos.A todos os funcionários do Departamento de Genética pelo apoio, amizade e condução dos experimentos, em especial a Antônio Juscelino Desidério, Ariberto Soares,
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