A Bayesian approach for assessing the stability of genotypes

Several statistical models can be used for assessing genotype X environment interaction (GEI) and studying genotypic stability. The objectives of this research were to show how (i) to use Bayesian methodology for computing Shukla's phenotypic stability variance and (ii) to incorporate prior information on the parameters for better estimation. Potato [Solanum tuberosum subsp. andigenum (Juz. & Bukasov) Hawkes], wheat (Triticum aestivum L.), and maize (Zea mays L.) multi environment trials (MET) were used for illustrating the application of the Bayes paradigm. The potato trial included 15 genotypes, but prior information for just three genotypes was used. The wheat trial used prior information on all 10 genotypes included in the trial, whereas for the maize trial, noninformative priors for the nine genotypes was used. Concerning the posterior distribution of the genotypic means, the maize MET with 20 sites gave less disperse posterior distributions of the genotypic means than did the posterior distribution of the genotypic means of the other METs, which included fewer environments. The Bayesian approach allows use of other statistical strategies such as the normal truncated distribution (used in this study). When analyzing grain yield, a lower bound of zero and an upper bound set by the researcher's experience can be used. The Bayesian paradigm offers plant breeders the possibility of computing the probability of a genotype being the best performer. The results of this study show that although some genotypes may have a very low probability of being the best in all sites, they have a relatively good chance of being among the five highest yielding genotypes.

Yield prediction and inbreeding of maize synthetics generated with lines and single crosses : classic probability

reduce costs and labor associated with predicting the genotypic mean (GM) of a synthetic variety (SV) of maize (Zea mays L.), breeders can develop SVs from L lines and s single crosses (SynL,SC) instead of L+2s lines (SynL). The objective of this work was to derive and study formulae for the inbreeding coefficient (IC) and GM of SynL,SC, SynL, and the SV derived from (L+2s)/2 single crosses (SynSC). All SVs were derived from the same L+2s unrelated lines whose IC is FL, and each parent of a SV was represented by m plants. An a priori probability equation for the IC was used. Important results were: 1) the largest and smallest GMs correspond to SynL and SynL,SC, respectively; 2) the GM predictors with the largest and intermediate precision are those for SynL and SynL,SC, respectively; 3) only when FL=1, or m is large, SynL and SynSC are the same population, but only with SynSC prediction costs and labor undergo the maximum decrease, although its prediction precision is the lowest. To determine the SV to be developed, breeders should also consider the availability of lines, single crosses, manpower and land area; besides budget, target farmers, target environments, etc.

Multidimensional cluster stability analysis from a Brazilian Bradyrhizobium sp RFLP/PCR data set

The taxonomy of the N(2)-fixing bacteria belonging to the genus Bradyrhizobium is still poorly refined, mainly due to conflicting results obtained by the analysis of the phenotypic and genotypic properties. This paper presents an application of a method aiming at the identification of possible new clusters within a Brazilian collection of 119 Bradryrhizobium strains showing phenotypic characteristics of B. japonicum and B. elkanii. The stability was studied as a function of the number of restriction enzymes used in the RFLP-PCR analysis of three ribosomal regions with three restriction enzymes per region. The method proposed here uses Clustering algorithms with distances calculated by average-linkage clustering. Introducing perturbations using sub-sampling techniques makes the stability analysis. The method showed efficacy in the grouping of the species B. japonicum and B. elkanii. Furthermore, two new clusters were clearly defined, indicating possible new species, and sub-clusters within each detected cluster. (C) 2008 Elsevier B.V. All rights reserved.

Genetic parameters and simultaneous selection for root yield, adaptability and stability of cassava genotypes

O objetivo deste trabalho foi estimar parâmetros genéticos e avaliar a seleção simultânea quanto à produtividade de raízes e à adaptabilidade e estabilidade de genótipos de mandioca. Os efeitos dos genótipos foram considerados como fixos e aleatórios, e a metodologia de modelos mistos (REML/Blup) foi utilizada para estimar os parâmetros genéticos e a média harmônica do desempenho relativo dos valores genotípicos (MHPRVG), para seleção simultânea. Dez genótipos foram avaliados em delineamento de blocos ao acaso, com quatro repetições. O experimento foi realizado nos municípios de Altamira, Santarém e Santa Luzia do Pará, PA, nos anos agrícolas de 2009/2010, 2010/2011 e 2011/2012. As raízes foram colhidas 12 meses após o plantio, em todos os locais testados. A produtividade de raízes apresentou baixo coeficiente de variação genotípica (4,25%) e herdabilidade de parcelas individuais no sentido amplo (0,0424), o que resultou em baixo ganho genético. Em razão da baixa correlação genotípica (0,15), a classificação dos genótipos quanto à produtividade de raízes variou de acordo com o ambiente. Os genótipos CPATU 060, CPATU 229 e CPATU 404 destacaram-se quanto à produtividade, adaptabilidade e estabilidade.

Productivity, stability and adaptability in open pollination progenies of Eucalyptus urophylla ST Blake

Prediction of genetic gains within breeding programs is not always compatible with those observed in practice. One reason for this inconsistency is the lack of knowledge of genotype-environment interaction (GxE). The aim of this study was to estimate genetic variation, evaluate the GxE, investigate the genetic correlation between pairs of environments and for the set, and to study the productivity, stability and adaptability at 2 years of age for diameter at breast height (DBH) in five progenies trials of Eucalyptus urophylla, used in a randomized complete block design, with the number of progenies ranging from 138 to 167, four to eight blocks and five to six plants per plot. Estimates of variance components and genetic parameters were obtained using the REML/BLUP method. For analysis of productivity, stability and adaptability, the HMRPGV method was used. The highest DBH growth was observed in Anhembi (10.52 cm) and Uberaba (10.20 cm). Estimates considered high were obtained for the coefficient of individual additive genetic variation (>13.3%) and average heritability among progenies (>0.40), indicating the possibility of obtaining genetic gains by selection among progenies. The coefficient of determination of the GxE was 1.7%, a fact that led to a high value of genotypic correlation between the performance of the progenies and environments (78.1%), indicating that the interaction is simple. The first six progenies showed a coincidence of 100% in the order of stability (HMGV), adaptability (RPGV) and productivity (HMRPGV), being 13% higher than the overall mean of five experiments (9.21 cm). When ordering the progenies, the selection of the 20 best in growth led to an increase in gain ranging of from 10.4 to 70%. Anhembi is the ideal place to have a breeding population which will be good in the other places as well.

Purity evaluation and influence of carbon nanotube on carbon nanotube/graphite thermal stability

High resolution thermogravimetry has been used to evaluate the carbonaceous content in a commercial sample of single-walled carbon nanotube (SWNT). The content of SWNTs in the sample was found to be at least 77mass% which was supported by images obtained with scanning and transmission electron microscopies (SEM and TEM). Furthermore, the influence of SWNT addition on the thermal stability of graphite in mixtures of SWNT/graphite at different proportions was investigated. The graphite stability decreased with the increased of SWNT content in the overall range of composition. This behavior could be due to the close contact between these carbonaceous species as determined by SEM analysis.

Static load modelling and voltage stability indices

This paper analyzes the performance of some of the widely used voltage stability indices, namely, singular value, eigenvalue, and loading margin with different static load models. Well-known ZIP model is used to represent loads having components with different power to voltage sensitivities. Studies are carried out on a 10-bus power system and the New England 39-bus power system models. The effects of variation of load model on the performance of the voltage stability indices are discussed. The choice of voltage stability index in the context of load modelling is also suggested in this paper.

Stability analysis and control of multiple converter based autonomous microgrid

In this paper, the stability of an autonomous microgrid with multiple distributed generators (DG) is studied through eigenvalue analysis. It is assumed that all the DGs are connected through Voltage Source Converter (VSC) and all connected loads are passive. The VSCs are controlled by state feedback controller to achieve desired voltage and current outputs that are decided by a droop controller. The state space models of each of the converters with its associated feedback are derived. These are then connected with the state space models of the droop, network and loads to form a homogeneous model, through which the eigenvalues are evaluated. The system stability is then investigated as a function of the droop controller real and reac-tive power coefficients. These observations are then verified through simulation studies using PSCAD/EMTDC. It will be shown that the simulation results closely agree with stability be-havior predicted by the eigenvalue analysis.

Sociometric stability and the behavioral correlates of peer acceptance in early childhood

This paper presents findings from an Australian study examining the behavioral correlates and stability of social status for preschool-aged children. The social status of an initial sample of 187 (94 boys and 93 girls) preschool children (mean age 62.4 months, SD = 4.22) was determined through sociometric assessment. Children classified as rejected, neglected and popular (n = 70) were selected for observation. Children were observed for a total of 25 minutes over a three-month period engaging in free play within their preschool centers. Results indicated that children classified as popular were more likely than rejected or neglected children to engage in cooperative play, ongoing connected conversation and to display positive affect. Popular children were less likely than rejected or neglected children to engage in parallel play, onlooker behavior or alone directed behavior. Six months after initial sociometric classification, sociometric interviews were repeated to test for stability and change. Results indicated that preschool-aged children’s social status classifications showed a moderate to high rate of stability for those children classified as popular, rejected and neglected.