A competição entre os recursos ambientais, imposta pela comunidade infestante, afeta o crescimento, produtividade e qualidade final da soja, prejudicando a colheita, por competição, que aumenta o custo operacional. Outro fator relevante da interferência das plantas infestantes é que estas podem ser hospedeiras de patógenos e pragas, o que dificulta seu controle. Este trabalho teve como objetivo avaliar o desempenho agronômico de duas cultivares de soja sujeitas à interferência de plantas infestantes. O experimento foi conduzido na área experimental da Fazenda Capim Branco pertencente à Universidade Federal de Uberlândia, no município de Uberlândia - MG, na safra 2015/2016. O delineamento experimental foi o de blocos ao acaso (DBC) com seis repetições. Foram utilizadas duas cultivares, uma de ciclo precoce (UFUS Capim Branco) e outra de ciclo tardio (UFUS Carajás), avaliadas na presença e ausência de plantas infestante, quanto à altura da planta na maturidade, número de nós na haste principal, número de vagens e produtividade de grãos. Após atender às pressuposições do modelo, os dados foram submetidos à análise de variância e ao teste de Tukey (p<0,05). Os resultados refletiram as relações de interferência entre a população de infestantes e a cultura, sendo a família Poaceae a infestante predominante no experimento. Houve aumento na altura média das plantas de soja, redução do número de nós e da produtividade de grãos em ambas cultivares. A cultivar UFUs Capim Branco, sob interferência de infestantes, obteve maior rendimento quando comparada a cultivar de ciclo tardio, UFUS Carajás.

ABSTRACT. The genetic diversity study has paramount importance in breeding programs; hence, it allows selection and choice of the parental genetic divergence, which have the agronomic traits desired by the breeder. This study aimed to characterize the genetic divergence between 24 soybean genotypes through their agronomic traits, using multivariate clustering methods to select the potential genitors for the promising hybrid combinations. Six agronomic traits evaluated were number of days to flowering and maturity, plant height at flowering and maturity, insertion height of the first pod, and yield. The genetic divergence evaluated by multivariate analysis that esteemed first the Mahalanobis' generalized distance (D 2 ), then the clustering using Tocher's optimization methods, and then the unweighted pair group method with arithmetic average (UPGMA). Tocher's optimization method and the UPGMA agreed with the groups' constitution between each other, the formation of eight distinct groups according Tocher's method and seven distinct groups using UPGMA. The trait number of days for flowering (45.66%) was the most efficient to explain dissimilarity between genotypes, and must be one of the main traits considered by the breeder in the moment of genitors choice in soybeanbreeding programs. The genetic variability allowed the identification of dissimilar genotypes and with superior performances. The hybridizations UFU 18 x UFUS CARAJÁS, UFU 15 x UFU 13, and UFU 13 x UFUS CARAJÁS are promising to obtain superior segregating populations, which enable the development of more productive genotypes.

Cotton is the most widely utilized natural fiber in the world. Brazil is currently one of the world's largest cotton producers. Cotton crops are cultivated in all regions of the country, especially in the Cerrado biome. Studies of genotype x environment (GxE) interactions evaluate the adaptability and stability of cotton genotypes. Adaptability and stability evaluations help understand genotype responses to environmental stimuli and the predictability of genotypes in their response to environmental oscillations. We examined the effect of the genotype x environment interaction on cotton yield and fiber characteristics and compared artificial neural networks (ANNs) with conventional methods for assessing adaptability and stability of colored-fiber cotton genotypes. The experiment was conducted at the experimental farm of Universidade D.B.O. Cardoso et al. 2 ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 18 (1): gmr18104 Federal de Uberlândia, during four crop years. Twelve genotypes of colored-fiber cotton were evaluated. The experimental design was randomized complete blocks with three replicates. Seed cotton yield was evaluated. The GxE interaction was analyzed by the F-test at α = 0.05. Adaptability, stability, and the factors of the decomposed GxE interaction were analyzed by the Eberhart and Russell, Centroid and ANN methods. The GxE interaction was significant for the variable seed cotton yield, demonstrating differences in genotype behavior among environments. The interactions were predominantly complex. There was concordance between Eberhart and Russsell and ANN analyses. Genotypes UFUJP-02 and UFUJP-17 were responsive to environmental stimuli; they had high predictability, in addition to high fiber yield. The ANN method reliably evaluated adaptability compared with Eberhartand Russel and Centroid methods.

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Plant breeders need to understand the genetic diversity and relationships between genotypes to choose parents of segregating populations. We evaluated the genetic diversity of 35 soybean genotypes and determined their potential as parent lines in breeding programs by analyzing their agronomic traits and microsatellite markers. Phenotypic analysis was carried out in the field at Fazenda Capim Branco, a research station of the Federal University of Uberlândia. Nine microsatellite markers and seven agronomic traits in were evaluated in 35 conventional soybean genotypes. Genotypes were grouped by UPGMA and Tocher cluster analyses, and molecular analysis was used to calculate polymorphism for each microsatellite locus. Nine microsatellite markers amplified 26 alleles, ranging from two to four. Polymorphism varied ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 19 (1): gmr18105 L.B. Sousa et al. 2between 0.29 and 0.66, and averaged 0.44. The number of days to maturity was the characteristic that contributed the most to yield (29.44%). Seven potential parents (G11, G12, G16, G21, G22, G26 and G33) had average grain yields higher than 5000 kg ha -1 . UPGMA and Tocher methods identified groups from the matrix of phenotypic and molecular data. Hybrids of G11, G12, G16, G22, G26 and G33 genotypes segregated promising populations with superior genetic variability.