30 Bioscience Journal Original Article Biosci. J., Uberlândia, v. 36, n. 1, p. 30-41, Jan./Feb. 2020 http://dx.doi.org/10.14393/BJ-v36n1a2020-42075 REPEATABILITY ESTIMATES AND MINIMUM NUMBER OF EVALUATIONS FOR SELECTION OF ELEPHANT-GRASS GENOTYPES FOR FORAGE PRODUCTION ESTIMATIVAS DE REPETIBILIDADE E NÚMERO MÍNIMO DE AVALIAÇÕES PARA SELEÇÃO DE GENÓTIPOS DE CAPIM-ELEFANTE PARA PRODUÇÃO DE FORRAGEM Erina Vitório RODRIGUES 1* ; Rogério Figueiredo DAHER 2 ; Geraldo de Amaral GRAVINA 2 ; Alexandre Pio VIANA 3 ; Maria do Socorro Bezerra de ARAÚJO 2 ; Maria Lorraine Fonseca OLIVEIRA 2 ; Marcelo VIVAS 2 ; Bruna Rafaela da Silva MENEZES 2 ; Antônio Vander PEREIRA 4 1. Universidade de Brasília, Campus Planaltina, DF, Brasil. erinavict@hotmail.com; 2. Laboratório de Engenharia Agrícola - Centro de Ciências e Tecnologias Agropecuárias, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brasil; 3. Laboratório de Melhoramento Genético Vegetal - Centro de Ciências e Tecnologias Agropecuárias, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brasil; 4. Embrapa Gado de Leite, Juiz de Fora, MG, Brasil Brasil. ABSTRACT. In forage-plants breeding, the selection of superior genotypes has been undertaken through successive harvests in previously established intervals. However, this process involves many steps, the evaluation of many traits, and a great spending with costs and labor. Thus the estimate of the repeatability is essential in improvement of perennials, it allows predicting genotypic value of the individual, the minimum number of evaluations in the selection of genotypes and minimizes resources and time in the selection of promising individuals. The objective of this study was to estimate the repeatability coefficient for morphological traits in elephant grass and determine the number of evaluations needed for phenotypic selection more efficient. The experimental randomized block design with 53 genotypes and two replications. The repeatability coefficients were estimated for variables plant height, number of tillers, stem diameter and dry matter yield, using the methods of Anova, Principal Components and Structural Analysis. We observed significant differences between genotypes (P <0.01) for all variables. The main components provide larger estimates of repeatability when compared to other methods. Estimates of the repeatability coefficients are of high magnitude average for the variables plant height (0.44) number of tillers (0.44) and stem diameter (0.63) and low magnitude for dry matter production (0.27). The Principal Components method requires five, five, two and eleven measurements for plant height, number of tillers, stem diameter and dry matter yield, respectively, with 80% reliability. KEYWORDS: Pennisetum purpureum S. Coefficient of determination. Main components. Dry matter yield. INTRODUCTION Tropical forage plants have a great importance in the Brazilian agricultural scenario, as they constitute the main feeding source for dairy and meat herds. In this regard, the elephant grass (Pennisetum purpureum Schum) stands out for its high herbage production (PEGORARO et al., 2009), as a species of high dry matter yield (7.3 - 14.5 t ha - 1 ) potential and high crude protein value (919.4 – 1591.0 kg ha -1 ) that adapts easily to adverse soil- climatic conditions (LIMA et al., 2007; PACIULLO et al., 2008; LIMA et al., 2011). These features make the elephant grass a highly promising crop in the animal production chain. In forage-plants breeding, the selection of superior genotypes has been undertaken through successive harvests in previously established intervals. However, this process involves many steps, the evaluation of many traits, and a great spending with costs and labor (OLIVEIRA et al., 2011). An alternative to minimize these challenges is the use of repeatability. By the estimate of the repeatability coefficient (r), it is possible to determine how many evaluations should be performed until the phenotypic evaluation shows high efficiency (CRUZ et al., 2012). The repeatability coefficient is defined statistically as the correlation between the measurements made in the same individual, whose Received: 01/05/18 Accepted: 10/02/19