Efeito do tamanho amostral na estimativa da herdabilidade em espécies perenes

No presente trabalho foram realizados estudos referentes ao tamanho amostral adequado a estimação da herdabilidade no sentido restrito em espécies perenes. Foram considerados aspectos teóricos da estimação da herdabilidade e os conceitos foram aplicados a dados experimentais associados a progênies de meios-irmãos de acácia-negra (Acacia mearnsii) avaliadas no Rio Grande do Sul. Os seguintes resultados foram obtidos: para uma precisa estimação da herdabilidade no sentido restrito recomendam-se os tamanhos amostrais aproximados de 8000, 4000 e 2600 dados para herdabilidades de 0,10; 0,20 e 0,30 respectivamente; o valor mais provável para a herdabilidade do caráter DAP em acácia-negra situa-se ao redor de 0,30; para estimação da média e variância fenotípica de um caráter quantitativo, a utilização de um tamanho amostral equivalendo a cerca de 1/3 do tamanho amostral adequado à estimação da variância aditiva e da herdabilidade já é suficiente para a obtenção de estimativas precisas; com tamanho amostral inferior a 1000 não se recomenda a estimação de parâmetro genéticos. Neste caso, a predição de valores genéticos deve ser realizada preferencialmente utilizando estimativas de parâmetros relatadas em literatura. Sample size effects on estimates of heritability in perennial species Abstract This paper describes aspects concerning to optimal sample size required for estimation of the strict sense heritability in perennial species. Theoretical concepts were applied to experimental data from Acacia mearnsii progeny test grown in Rio Grande do Sul. For a precise estimation of the heritability, sample sizes of 8000, 4000 and 2600 were recommended for heritabilities of 0,10; 0,20 and 0,30 respectively. The most probable value for the heritability of the character DBH in black wattle locates about of 0,30. For estimation of the average and phenotypic variance of a quantitative character, the use of a sample size of about 1/3 of that recommended for estimation of the additive variance and of the heritability is adequate. Sample sizes below 1000 are not suitable for genetic parameters estimation. In this case, standard values of genetic parameters (obtained from literature) should be used in the breeding values prediction procedures

Genomic growth curves of an outbred pig population

The success of pig production systems, including the evaluation of alternative management and marketing strategies, requires knowledge of the body weight behavior over time, commonly referred to as the growth curve. This knowledge allows the assessment of growth characteristics in actual production situations and translates this information into economic decisions. Differences among animal growth curves partly reflect genetic influences, with multiple genes contributing at different levels to the overall phenotype. Hence, selection strategies that attempt to modify the growth curve shape to meet demands of the pork market are very relevant. In the current post-genomic era, understanding the genomic basis of pig growth cannot be limited to simply estimating marker effects using body weight at a specific time as a phenotype, but must also consider changes in body weight over time. According to Pong-Wong and Hadjipavlou (2010) and Ibáñez-Escriche and Blasco (2011) this can be done by estimating the marker effects for parameters of nonlinear regression models that are widely used to describe growth curves. Regardless of the phenotype used, a major challenge in genome-wide selection (GS) is to identify the most powerful statistical methods for predicting phenotypic values based on estimates of marker effects. Since the seminal GS paper by Meuwissen et al. (2001), several studies have compared the efficiency of simple methods, such as the RR-BLUP (Random Regression Blup) (Meuwissen et al., 2001), with more sophisticated methods, such as Bayesian LASSO (BL) (de los Campos et al., 2009). The main difference between these two very popular GS methods is that the first one assumes, a priori, that all loci explain an equal amount of genetic variation, while the second one allows the assumption that each locus explains its own amount of this variation. Although these two methods have already been compared in other studies, so far there has been no comparison of these methods using a major gene, such as the halothane gene in pigs (Fujii et al., 1991), as a marker. In addition, these methods have not yet been applied to the analysis of growth curves in conjunction with nonlinear regression models. In this study, we compared the accuracies of RR-BLUP and BL for predicting genetic merit in an empirical application using weight-age data from an outbred F2 (Brazilian Piau X commercial) pig population (Silva et al., 2011). In this approach, the phenotypes were defined by parameter estimates obtained with a nonlinear logistic regression model and the halothane gene was considered a single nucleotide polymorphism (SNP) marker in order to evaluate the assumptions of the GS methods in relation to the genetic variation explained by each locus. Genomic growth curves based on genomic estimated breeding values were constructed and the most relevant SNPs associated with growth parameters were identified

Air-drying of eucalypts logs: Genetic variations along time and stem profile

Knowledge of wood drying potential is relevant in forestry and biomaterials technology field, being directly related with timber transport, lumber properties, charcoal yield and pulping process. Using mixed models approach by REML-BLUP procedure, we aimed to evaluate the moisture content loss potential among different eucalypt genotypes, by means of genetic correlations, heritabilities, coefficients of variation and determination of wood air-drying over 154 drying days and in five tree stem heights. Moreover, we tested three possible auxiliary traits (Heartwood/Sapwood ratio, Log Circumference, and Basic Wood Density) for indirect selection on wood air-drying rate. The highest air-drying heritabilities occurred at the two most basal stem heights and only after the 98th day. However, genetic correlations across the drying measurements were considerably high from day 42. The three auxiliary traits demonstrated potential for indirect selection, suggesting the possibility of integrating wood air-drying to future Eucalyptus sp. breeding programs. There is no need to wait for industrial moisture content to carry out genetic evaluation. Besides, perform selection at trees basal region is the safest way to improve the air-drying rate of genotypes

Genome-wide association and regional heritability mapping of plant architecture, lodging and productivity in Phaseolus vulgaris

The availability of high-density molecular markers in common bean has allowed to explore the genetic basis of important complex agronomic traits with increased resolution. Genome-Wide Association Studies (GWAS) and Regional Heritability Mapping (RHM) are two analytical approaches for the detection of genetic variants. We carried out GWAS and RHM for plant architecture, lodging and productivity across two important growing environments in Brazil in a germplasm of 188 common bean varieties using DArTseq genotyping strategies. The coefficient of determination of G · E interaction (c 2 int ) was equal to 17, 21 and 41%, respectively for the traits architecture, lodging, and productivity. Trait heritabilities were estimated at 0.81 (architecture), 0.79 (lodging) and 0.43 (productivity), and total genomic heritability accounted for large proportions (72% to 100%) of trait heritability. At the same probability threshold, three marker–trait associations were detected using GWAS, while RHM detected eight QTL encompassing 145 markers along five chromosomes. The proportion of genomic heritability explained by RHM was considerably higher (35.48 to 58.02) than that explained by GWAS (28.39 to 30.37). In general, RHM accounted for larger fractions of the additive genetic variance being captured by markers effects inside the defined regions. Nevertheless, a considerable proportion of the heritability is still missing ( 42% to 64%), probably due to LD between markers and genes and/or rare allele variants not sampled. RHM in autogamous species had the potential to identify larger-effect QTL combining allelic variants that could be effectively incorporated into whole-genome prediction models and tracked through breeding generations using marker-assisted selection

Avaliação genética em erva-mate pelo procedimento BLUP individual multivariado sob interação genótipo x ambiente Genetic evaluation in Ilex paraguariensis by the multivariate individual BLUP procedure with genotype-environment interaction

Os objetivos deste trabalho foram estimar parâmetros genéticos e fenotípicos e realizar a predição de valores genéticos de matrizes e procedências de erva-mate (Ilex paraguariensis). Foram avaliadas 164 progênies de oito procedências, em três locais (Ivaí, PR, Guarapuava, PR e Rio Azul, PR), em relação ao caráter produção de massa foliar (PMF). Os componentes de variância, parâmetros genéticos e valores genéticos foram estimados pelo procedimento REML/BLUP individual (máxima verossimilhança restrita/melhor predição linear não viciada), realizando a análise multivariada para os três locais. Os coeficientes de herdabilidade individual, no sentido restrito, para o caráter PMF foram 0,15 em Ivaí, 0,62 em Guarapuava e 0,23 em Rio Azul. A baixa magnitude desses coeficientes em Ivaí e Rio Azul demanda a utilização de métodos de seleção que utilizem todos os efeitos aleatórios do modelo estatístico. O efeito de procedências foi significativo em Ivaí e Rio Azul, com correlação fenotípica intraclasse de 0,13 em Ivaí e de 0,09 em Rio Azul. As procedências apresentaram correlação genética de 0,95 entre os locais Ivaí e Rio Azul. Nesses locais, as procedências foram mais estáveis nos diferentes ambientes do que as progênies. Foram preditos os valores genéticos em relação a todas as procedências e matrizes em todos os locais quanto ao caráter avaliado. As melhores procedências são Barão de Cotegipe, Quedas do Iguaçu, Cascavel e Ivaí.<br>The objectives of this paper were to estimate genetic and phenotypic parameters and to predict breeding values for parents and provenances of Ilex paraguariensis. Eight provenances with 164 progenies were evaluated on three sites (Ivaí, PR, Guarapuava, PR and Rio Azul, PR) for the trait leaf weight (LW). All the variance components, parameters and breeding values were obtained by REML/BLUP (restricted maximum likelihood/best linear unbiased prediction) procedure at the individual level, through multivariate analysis involving the three sites. The individual strict sense heritabilities for the trait LW were 0.15 in Ivaí, 0.62 in Guarapuava and 0.23 in Rio Azul, demanding more sophisticated selection methods in Ivaí and Rio Azul. The provenance effect was significant in Ivaí and Rio Azul, with intraclass phenotypic correlation of 0.13 in Ivaí and 0.09 in Rio Azul. The provenances were more stable across sites than progenies with genetic correlation of 0.95 between the sites Ivaí and Rio Azul. Genetic values for all provenances and parents in all sites were predicted for the trait LW. The best provenances are Barão de Cotegipe, Quedas do Iguaçu, Cascavel and Ivaí