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The objetive of this work was to evaluate the influence of intergenotypic competition in open-pollinated families of Eucalyptus and its effects on early selection efficiency. Two experiments were carried out, in which the timber volume was evaluated at three ages, in a randomized complete block design. Data from the three years of evaluation (experiment 1, at 2, 4, and 7 years; and experiment 2, at 2, 5, and 7 years) were analyzed using mixed models. The following were estimated: variance components, genetic parameters, selection gains, effective number, early selection efficiency, selection gain per unit time, and coincidence of selection with and without the use of competition covariates. Competition effect was nonsignificant for ages under three years, and adjustment using competition covariates was unnecessary. Early selection for families is effective; families that have a late growth spurt are more vulnerable to competition, which markedly impairs ranking at the end of the cycle. Early selection is efficient according to all adopted criteria, and the age of around three years is the most recommended, given the high efficiency and accuracy rate in the indication of trees and families. The addition of competition covariates at the end of the cycle improves early selection efficiency for almost all studied criteria.

O objetivo deste trabalho foi estudar diferentes covariáveis de competição em análises de vizinhança, e verificar sua eficiência no aumento da precisão experimental e as consequências no ordenamento de genótipos de cana-de-açúcar em termos de potencial produtivo. Foram utilizados dados da rede de ensaios do programa de melhoramento de cana-de-açúcar do Instituto Agronômico, instalados em 2002. O delineamento foi em blocos ao acaso, com três repetições. As parcelas constituíram-se de cinco sulcos de 8 m, espaçados 1,50 m entre si. A produtividade de colmos por hectare (TCH, Mg ha-1) foi avaliada no primeiro e terceiro cortes. As covariáveis "lateral", "ponta" e "quatro vizinhos" foram incluídas nos métodos de Papadakis, em duas variações do método médias móveis. Os métodos de Papadakis e médias móveis 1 não alteraram a precisão experimental em comparação à análise tradicional. O método médias móveis 2 reduziu a variância ambiental, mas alterou as estimativas da variância genotípica e o ordenamento dos genótipos, o que pode induzir a conclusões equivocadas na seleção. Embora a covariável "lateral" tenha sido influente na competição, o efeito em parcelas de cinco sulcos é pequeno.The objective of this work was to study different competition covariates in neighborhood analysis and to check the efficiency of this analysis in the increase of the experimental precision and the consequences in the ranking of sugarcane genotypes in terms of productive potential. Data used were from the state experimental network of the sugarcane breeding program installed in 2002, of the Instituto Agronômico, Campinas, SP, Brazil. The experimental design was in randomized complete blocks, with three replicates. The plots were formed of five 8 m rows with 1.5-m spacing between rows. The stalk productivity (TCH, Mg ha-1) was evaluated in the first and third harvests. The covariates "side", "tip" and "4 neighbors" were included in the Papadakis method and in two variations of the moving average method. The Papadakis and moving average 1 methods did not change the experimental precision in comparison with traditional analysis. The moving average 2 method reduced the environmental variance. However, it changed the estimates of the genetic variance and the genotype ranking, and could lead to erroneous conclusions in the selection. Although the "side" covariate was influential on competition, its effect or on five row-plots was small.