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

Estimates of genetic parameters with selection within and between half-sib families of Jatropha curcas L.

Jatropha curcas L., the most promising oilseed plant for biodiesel and biokerosene, is in the process of domestication, and the economic, social and environmental viability of the crop depends on increasing its yield performance. Low seed yield is due, above all, to planting of non-improved cultivars. We evaluated 16 half-sib families in the 2nd, 3rd and 4th years after planting. The components evaluated were seed yield, number of trusses per plant, number of fruits per truss, fruit maturation rate, plant height and canopy diameter. We also estimated the genetic parameters of these components with a view toward quantifying genetic gain from plant selection. The main seed yield components exhibited predominant genetic control. Nevertheless, the environmental effect was the main determinant of uniformity in fruit maturation. Thus, management strategies have greater potential for having an impact on concentration of fruit production of this oilseed plant. Genetic gains related to seed yield in the cropping of genotypes selected in the 2nd, 3rd, and 4th years were 33.3%, 41.6% and 56.7%, respectively. The development of new genotypes should furthermore consider strategies for generation of variability using crosses between divergent plants with better agronomic characteristics

Intra-genotypic competition of Eucalyptus clones generated by environmental heterogeneity can optimize productivity in forest stands

The growth structure of Eucalyptus plantations is the result of site environment, genetic material, and different types of interaction between neighboring plants. It is well known that sites that are more homogeneous result in greater forest productivity. However, additional factors inherent in the micro- environment or the quality of cuttings can lead to heterogeneous clonal biomass at the end of the rotation cycle. This study of the growth patterns in commercial stands of Eucalyptus clones had two aims: (i) to determine whether environmental heterogeneity causes competition among genetically identical individuals and (ii) to validate the occurrence of intra-genotypic competition, revealing the potential relationship with forest productivity. The present study was developed based on two linear mixed models: a non-genetic model, which accounts for spatial autocorrelation and is used to estimate the effects of competition between neighboring trees into the single clone plots; and a genetic model to infer the nature of the clonal competition. Three hundred and six square plots containing one hundred plants from eight experiments using a randomized block design, with three replications, were evaluated. The experiments were positioned in different environmental conditions by combining two different plant spacings and two altitude elevations. Using the path analysis procedure, we verified that there were significant direct effects of competition according to the proximity of the trees in the plot. In addition, trees that were more distant caused indirect effects of competition through nearby trees. Stands with uniform growth conditions (measured by residual autocorrelation parameters) actually caused higher productivity. The results from the genetic correlations of intra-genotypic competition and productivity showed that the less competitive clones were always less productive, regardless of the experimental condition. The more competitively aggressive clones could optimize their productivity when planted in sites with high residual levels, reaching productivities similar to those of homogeneous stands. This suggests that the implementation of certain silviculture techniques, seeking to increase site uniformity, is less relevant to these clones. The selection and use of these clones might be useful for large companies, because they offer the opportunity to achieve high productivity, and for smaller producers who do not have access to the silvicultural quality used by large companies

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