Estimativas de repetibilidade para caracteres forrageiros em Panicum maximum

Abstract

RESUMOObjetiva-se com este trabalho estimar a repetibilidade para caracteres forrageiros de Panicum, e determinar o número de cortes de avaliação necessários para a seleção de genótipos de Panicum, com confiabilidade. Utilizaram-se os dados de um ensaio conduzido no período de 21/11/2002 a 08/04/2005, no Campo Experimental da Embrapa Gado de Leite, localizado em Valença-RJ, onde foram realizados 15 cortes de avaliação. No ensaio, foram avaliados 23 genótipos de Panicum maximum, em parcelas experimentais, dispostas no delineamento de blocos casualizados, com três repetições. Foram estimados os coeficientes de repetibilidade para as características produção de matéria verde de forragem (PMV); produção de matéria seca de forragem (PMS) e de folhas (PMSF); porcentagem de folhas na PMS (%FOL) e altura da planta (AP), utilizando os métodos da análise de variância, componentes principais e análise estrutural. Para todas as características avaliadas os efeitos de genótipos, cortes e interação genótipos x cortes foram significativos (P<0,01). Quando se considerou o coeficiente de determinação de 85%, o número de avaliações (cortes) necessários para a determinação do valor real dos genótipos foram de 10, 9, 7, 11 e 3, respectivamente, para PMV, PMS, PMSF, %FOL e AP. O método dos componentes principais e o da análiseestrutural (baseado na matriz de correlações) foram concordantes para todas as características avaliadas. A realização de 10 cortes de avaliação permite discriminar o valor real dos genótipos de Panicum, com confiabilidade superior a 85%, para a maioria das características avaliadas.Termos para indexação: Forrageira, gramínea, componentes principais, análise estrutural, coeficiente de repetibilidade. ABSTRACTThe objective of this work was to estimate the repeatability for forage characters of Panicum and to determinate the necessary number of evaluation cuts to select Panicum genotypes with confidence. Data of a trial with 15 cuts, carried out between 21/11/2002 and 08/04/2005 in the experimental station of Embrapa Gado de Leite located in Valença, RJ, Brazil, were used. In this study. 23 genotypes of Panicum maximum were evaluated, in a complete randomized block, with three replications. The coefficient of repeatability for fresh forage production (PMV), total plant dry matter production (PMS) and leaves dry matter production (PMSF) were recorded along with leaves percentage in PMS (%FOL) and plant hight (AP), using the variance analysis, main components and structural analysis methods. For all evaluated parameters the effects of genotype, cut and genotype x cut interaction were significant (P<0.01). When considering the determination coefficient as 85%, the required number of measures (cuts) to determine the real value of genotypes were 10, 9, 7, 11 and 3, for PMV, PMS, PMSF, %FOL and AP, respectively. Main components and structural analysis methods (based on the correlation matrix) did agree for all features evaluated. The utilization of data from 10 cuts allows to discriminate, with confidence higher than 8...

<b>Repeatability, number of harvests, and phenotypic stability of dry matter yield and quality traits of Panicum maximum jacq.

“…2, through ANOVA and Principal Component Correlation (PCCor) methods, respectively. ANOVA consistently came up with the lowest estimates while PCCor the highest, similar to other reports (Martuscello et al, 2007, Lédo et al, 2008, Braz, Fonseca, Jank, Cruz, & Martuscello, 2015. The magnitude of the estimates in Exp.…”

“…No individual repeatability method gives precise estimation of the number of repeated measures for DMY over wide ranges of conditions, such as years and experimental sites, different genetic composition of the populations and time of harvest. The differences between methods in six studies (Martuscello et al, 2007, Lédo et al, 2008, Torres et al, 2016, and Exp. 1 and Exp.…”

“…Results from both studies concluded that at least five harvests are needed to have an effective selection with 0.85 accuracy. Repeatability estimates from 15 harvests (Lédo et al, 2008) ranged from 0.23 to 0.54 for DMY and for the same 0.85 level of accuracy it is necessary at least ten harvests. Torres et al (2016) reported high repeatability from six harvests, ranging from 0.76 to 0.87 and accuracy levels from 0.94 and 0.98.…”

Estimation of genetic parameters and selection of Brachiaria humidicola progenies using a selection index

“…The presence of this interaction indicates that the performance of the progenies was not consistent across the cuts for these characters. A similar result was observed by Lédo et al (2008) in an evaluation of 23 genotypes of Panicum maximum and of 17 clones of Pennisetum purpureum Schum by Daher et al (2004).…”

Repeatability of agronomic traits in Panicum maximum (Jacq.) hybrids

“…Regarding the different methods used to estimate the coefficient of repeatability, the lower values predicted by ANOVA and the higher values predicted by the multivariate models were also observed in other studies evaluating P. maximum genotypes (Cargnelutti Filho et al, 2004;Martuscello et al, 2007;Lédo et al, 2008). According to Martuscello et al (2007), the different estimates of repeatability coefficients obtained by the adopted methods indicate the need to employ multiple methods to obtain a precise interval within which the actual value of the parameter can be found with a greater probability.…”