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ABSTRACT. Defining selection criteria is important to obtain promising genotypes in a breeding program. The objective of this study was to estimate genetic parameters for agronomic traits and to perform soybean line selection using selection indices. The experiment was conducted at an experimental area located at Capim Branco farm, belonging to the Federal University of Uberlândia. A total of 37 soybean genotypes were evaluated in randomized complete block design with three replicates, in which twelve agronomic traits were evaluated. Analysis of variance, the Scott-Knott test at the 1 and 5% level of probability, and selection index analyses were performed. There was genetic variability for all agronomic traits, with medium to high levels of genotype determination coefficient. Twelve lines with a total cycle up to 110 days were observed and grouped with the cultivars MSOY 6101 and UFUS 7910. Three lines, UFUS FG 03, UFUS FG 20, and UFUS FG 31, were highlighted regarding grain yield with higher values than the national average of 3072 kg/ha. The direct selection

Keywords Glycine maxGrain yield Agronomic traits This work aimed to study agronomic traits of soybean genotypes by path analysis and correlation estimates. We have used a randomized complete block design to assess 35 soybean genotypes with three replications, which 31 lines were from the breeding program of the Federal University of Uberlândia, Brazil, plus four commercial cultivars. We have assessed features number of days to the blooming, plant height at blooming, number of days to maturity, plant height at maturity, first pod height, number of nodes on the main stem at maturity, number of pods with one, two and three seeds per plant, total number of pods per plant, number of seeds per pod and grain yield. The features plant height at maturity and number of nodes at maturity have presented significant correlations phenotypic and genotypic positive. 100-seed weight was positively correlated with grain yield shown high direct phenotypic and genotypic effects being, therefore, useful for indirect selection aiming the grain yield increase. Highlighted ConclusionThe approaches correlation and path analysis of agronomic traits of major importance in soybean lines are efficient in assessing interconnections between yield and other agronomic traits in soybean. The features plant height at maturity and number of nodes are positively correlated. 100-seed weight is positively correlated to grain yield, and correlations between the number of days to the blooming and average weight of 100 seeds are negative.Correlation coefficients are dimensionless and might fluctuate, positively or negatively, over a range from -1 to 1 (Cruz et al. 2012); it is a intensity measure of linear association between two variables. Correlation coefficients might be phenotypic, genotypic and environmental; its main function is to evaluate the relation between the traits. Phenotypic correlation is estimated by phenotypic measures which are made up by genetic and environmental causes. Therefore, genotypic correlation is the genetic portion of the phenotypic correlation used in breeding programs; because only genes can be inherited by the offspring (Ferreira et al. 2003).Knowledge of characteristics correlated to grain yield allows the breeder to use additional information in order to either, rule out or precisely promote genotypes of interest (Pandini et al. 2002). Rodrigues et al. (2010) claim that simple correlation coefficients do not represent the relationship of cause and effect between characteristics. It is because the high correlation between two characters can be misleading due the indirect effect promoted by other features (Dewey and Lu 1959). Therefore, Wright (1921) developed a method in order to better understand the causes of associations between characters originated from the analysis of correlations, which is called path analysis. This method allows unfolding the correlations into direct and indirect effects of variables in just on a base variable (Wright 1921).

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Resumo -A busca de alta produtividade na cultura da soja, sem onerar os custos de produção, é o objetivo do melhoramento genético. A cultivar UFUS Impacta é um genótipo de soja proveniente do cruzamento entre Cristalina RCH e IAC 100, de ciclo semi-tardio, com produtividade média superior às testemunhas Garantia e Emgopa 313 RCH. É resistente às principais moléstias da soja e indicada para cultivo no Estado de Minas Gerais.Termos para indexação: Glycine max, melhoramento genético, genótipo. UFUS Impacta: new soybean cultivar for Minas Gerais StateAbstract -The search for soybean high yield without production costs increasing is the objective of genetic improvement. Cultivar UFUS Impacta is a soybean genotype originated from the cross between Cristalina RCH and IAC 100, semi-late maturity group, with an average productivity greater than the cheks Garantia and Emgopa 313 RCH. It is resistant to major soybean pathogens, and it is indicated for cultivation in the State of Minas Gerais, Brazil.Index terms: Glycine max, genetic breeding, genotype. IntroduçãoO problema crônico da fome no mundo e o crescimento constante da população humana demandam a produção de mais alimentos, sem que se comprometa a base dos recursos. A área cultivável do nosso planeta tem limitações físicas para sua expansão, e por essa razão, o aumento da produtividade das culturas é a solução mais viável, porque é econômica, além de ser ecologicamente sustentável.Entre as tecnologias que incrementam a produtividade, a mais desejável é o uso de materiais genéticos superiores, o que é conseguido via melhoramento genéti-co capaz de viabilizar essa meta a custo reduzido. A constante substituição de cultivares por novos materiais, mais produtivos e resistentes às principais moléstias, é uma necessidade, visto que a estabilidade da cultura depende de materiais melhorados. As cultivares tornam-se obsoletas, em prazo relativamente curto, fazendo-se necessária sua permanente substituição (Bueno et al., 1999).Parte significativa do aumento de produtividade mé-dia de soja se dá em conseqüência do melhoramento genético. Por isso, futuros ganhos de produtividade e redução do tempo necessário para se atingir o máximo potencial dependem dos programas de melhoramento (Kihl & Almeida, 2000). Características da cultivarO programa de melhoramento genético da Universidade Federal de Uberlândia vem, desde 1995, realizando hibridações para desenvolver cultivares superiores. A cultivar UFU 801, protegida e registrada como UFUS Impacta, é produto de hibridações entre as cultivares Cristalina RCH e IAC 100. Foi testada, conforme exigências da Lei de Proteção de Cultivares, e recomendada para cultivo no Estado de Minas Gerais, por apresentar desempenho superior ao das testemunhas Garantia e Emgopa 313 RCH, que lhe serviram de comparação. Apresenta resistência às doenças: mancha olhode-rã -Cercospora sojina -, vírus do mosaico comum, míldio -Peronospora manshurica -, pústula bacteriana