The objective of this study was to investigate the genetic mechanisms of soybean resistance to Asian rust (Phakopsora pachyrhizi Syd. & P. Syd). F2 and F3 generations from 15 diallel crosses involving six soybean cultivars, EMBRAPA 48, BRS 154, BRS 184, BRS 214, BRS 231, were used to analyze the genetic control of Asian rust resistance in the soybean parents tested. Genetic models were fitted to means and variances of the generations tested in a completely randomized field experiment with 5,700 hill plots. The experiment was spray-inoculated twice with an isolate that was first detected during the 2002/03 season in Mato Grosso (MT) State and presently prevail in Central Brazil, at a sixday interval, on borders rows and on the useful area, respectively, with a 10 4 spores/ml distilled H 2 O suspension. Assessments were made using a diagrammatic scale for disease severity at seven and 39 days after the first detection of Asian rust in the experiments. Evaluations made in the second assessment (39 days) discriminated better between genotypes. Selection at early plant developmental stages may not result in adult resistant plants. Cultivar FT-2, which had presented monogenic resistance to a rust isolated that prevailed in the first two years of rust occurrence in Brazil, showed no resistance to the MT State rust strain used in this experiment, but eleven crosses showed genetic variability for resistance in the second assessment. Soybean rust resistant genes showing predominantly additive effects are dispersed among parents. Narrow sense heritability values ranging from 0.42 to 0.74 at the F3 family level in the second assessment suggested that selection of resistant genotypes is feasible.

Asian soybean rust (ASR), caused by the phytopathogenic fungi Phakopsora pachyrhizi, has caused large reductions in soybean (Glycine max) yield in most locations in Brazil where it has occurred since it was first reported in

-The objective of this work was to identify the best selection strategies for the more promising parental combinations to obtain lines with good resistance to soybean Asian rust (Phakopsora pachyrhizi). Two experiments were carried out in the field during the 2006/2007 and 2007/2008 growing seasons, to determine the percentage of infected leaf area of individual plants of five parents and their segregant F 2 and F 3 populations. The data obtained indicates that additive genetic variance predominates in the control of soybean resistance to Asian rust, and that the year and time of assessment do not significantly influence the estimates of the genetic parameters obtained. The narrow-sense heritability (h 2 r ) ranged from 23.12 to 55.83%, and indicates the possibility of successful selection of resistant individuals in the early generations of the breeding program. All the procedures used to select the most promising populations to generate superior inbred lines for resistance to P. pachyrhizi presented similar results and identified the BR01-18437 x BRS 232 population as the best for inbred line selection.Index terms: Glycine max, Phakopsora pachyrhizi, additive variance, heritability, selection. Estratégias de seleção de populações segregantes de soja para resistência à ferrugem-asiáticaResumo -O objetivo deste estudo foi identificar as estratégias mais eficientes para selecionar as combinações parentais mais promissoras e obter linhas com bom grau de resistência à ferrugem-asiática da soja (Phakopsora pachyrhizi). Dois experimentos foram realizados em campo nos anos agrícolas 2006/2007 e 2007/2008, para avaliar a percentagem da área foliar infectada em plantas individuais de cinco parentais e das suas populações segregantes F 2 e F 3 . Os dados obtidos indicam que a variância genética aditiva predomina no controle da resistência da soja à ferrugem-asiática e que os anos e as épocas de avaliação não influenciaram significativamente as estimativas dos parâmetros genéticos obtidos. A herdabilidade no sentido restrito (h 2 r ) variou de 23,12 a 55,83%, o que indica a possibilidade de sucesso com a seleção de indivíduos resistentes em gerações precoces nos programas de melhoramento. Todos os procedimentos usados para selecionar as populações mais promissoras na geração de linhagens superiores quanto à resistência a P. pachyrhizi apresentaram resultados similares e identificaram a população BR01-18437 x BRS 232 como a melhor para a seleção de linhagens.Termos para indexação: Glycine max, Phakopsora pachyrhizi, variância aditiva, herdabilidade, seleção.

-The objectives of this work were to identify parents resistant to Asian soybean rust using diallel crosses, obtain information on the genetic control of soybean resistance to the pathogen and verify whether the combining ability estimates interact with the environment (year or time of assessment). The F 1 generation was obtained in a greenhouse from crosses between fi ve contrasting parents for the trait resistance to soybean rust, in a complete diallel without reciprocals. Two rust-severity assessments were carried out on individual soybean plants of 25 treatments (parents and F 2 and F 3 populations) in 2006/2007 and 2007/2008, in an experimental fi eld at Embrapa Soja, Londrina, PR, Brazil. Additive effects predominated in the genetic control of soybean resistance to Asian rust, and the interaction of the segregant populations with the environment, although signifi cant, did not alter the genetic parameter's general combining ability (GCA) and specifi c combining ability estimates, indicating that estimates obtained in one year and one assessment can be extrapolated to others. BR01-18437 inbred line is resistant to Asian rust and showed high GCA effects. This line should be used as parent if the objective is the resistance to Phakopsora pachyrhizi.Index terms: Glycine max, Phakopsora pachyrhizi, general combining ability, specifi c combining ability. Interferência da interação genótipos x ambientes no controle genético da resistência à ferrugem asiática da sojaResumo -Os objetivos deste trabalho foram identifi car genitores resistentes à ferrugem asiática da soja por meio de cruzamentos dialélicos, obter informações sobre o controle genético da resistência ao patógeno e verifi car se as estimativas da capacidade combinatória interagem com o ambiente (ano ou época de avaliação). A geração F 1 foi obtida por meio de cruzamentos entre cinco genitores contrastantes para a característica resistência à ferrugem da soja, em um dialelo completo, sem os recíprocos, em casa de vegetação. Foram realizadas duas avaliações quanto à severidade da ferrugem asiática da soja em plantas individuais de 25 tratamentos (genitores e populações F 2 e F 3 ) em 2006/2007 e 2007/2008, no campo experimental da Embrapa Soja, em Londrina, PR. Houve predominância de efeitos aditivos no controle genético da resistência à ferrugem asiática da soja, e a interação das populações segregantes com os ambientes, embora signifi cativa, não alterou as estimativas dos parâmetros genéticos da capacidade geral de combinação (CGC) e da capacidade específi ca de combinação, indicando que as estimativas obtidas em um ano e uma avaliação podem ser extrapoladas para outros. A linhagem endogâmica BR01-18437 é resistente à ferrugem asiática e apresenta alta estimativa de CGC, e deve ser utilizada como genitora quando o objetivo é a resistência a Phakopsora pachyrhizi.Termos para indexação: Glycine max, Phakopsora pachyrhizi, capacidade geral de combinação, capacidade específi ca de combinação.

RESUMOOs objetivos desse tra ba lho fora m estu da r a resistência e/ou tolerância da soja à ferrugem-asiática, expresso por genes maiores e menores e seleciona r as linha gens resistentes e/ou tolera ntes mais produtivas. Foram utilizados dados de seis experimentos realizados na s safras 20 05/20 06, 20 06 /20 07 e 2 00 7/2 008 , em Londrina , PR, envolvendo cinco parentais e as gerações segregantes F 2 , F 3 e F 4 . Foi u tiliza do o delinea mento inteira mente ca su a liza do u tiliza ndo a metodologia de cultivo em covas (01 parcela = 01 cova = 01planta). Os resultados indicaram que a resistência e/ou tolerância genética à ferrugem-asiática é controlada por genes maiores e menores dispersos Lima, W.F.; Prete, C.E.C.; Ribeiro, A.S.; Toledo, J.F.F. Resistência da soja à ferrugem-asiática avaliada pela análise da produtividade de grãos. Summa Phytopathologica, v.38, n.1, p.73-78, 2012.Palavras-chave adicionais: Phakopsora pachyrhizi, Glycine max, controle genético, resistência à doença, melhoramento de soja. nos pa renta is qu e expressam a ção predominantemente aditiva. Os da dos ta mbém indica ra m qu e sob pressã o de inócu lo é possível selecionar linhagens de soja com produtividades de grãos superiores a o pa renta l com ma ior produ tivida de de grã os na ma ioria dos cruzamentos, indicando que a seleção resultou em genótipos resistentes e/ou tolerantes. A herdabilidade no sentido restrito da produtividade de grãos, na presença da ferrugem-asiá tica, variou de média a a lta (0,324 a 0,815) ao nível de progênies F 3 , demonstrando ser possível selecionar progênies resistentes e/ou tolerantes à ferrugem-asiática já nas gerações iniciais dos programas de melhoramento.T he ma in objectives of this work were to stu dy the soybea n resistance and/or tolerance to Asian rust and to select the inbred lines more productive in relation to Asian rust. Data from six experiments involving the parental lines and their F 2 , F 3 and F 4 generations were used in this experiment. It was carried out in Londrina, Parana state, du ring the 2 0 0 5 /0 6 , 2 0 0 6 /0 7 and 2 0 0 7 /0 8 cropping sea sons. A completely randomized experiment with individu al pla nts sown in Lima, W.F.; Prete, C.E.C.; Ribeiro, A.S.; Toledo, J.F.F. Resistance of soybean to Asian rust assessed by grain yield analysis. Summa Phytopathologica, v.38, n.1, p.73-78, 2012.hill plot was used (01 hill plot = 01 plant). Soybean resistance and/or tolera nce to Asia n ru st is controlled by ma jor a nd minor genes expressing mainly additive effects dispersed in the parents. It is possible to select inbred lines superior to the best yielding parent from most crosses. T he narrow sense heritability for the yield trait under rust pressu re ra nged from avera ge to high (0 .32 4 to 0 .8 15 ) at the F 3 progeny level, which warrants gains from selection.Keywords: Phakopsora pachyrhizi, Glycine max, genetic control, disease resistance, soybean breeding. ABSTRACTA soja (Glycine max (L.) Merrill) é uma das principais culturas do Brasil. Na safra de 2010/2011 a área cul...

Soybean is one of the most important crops in Brazil and continuously generates demands for production technologies, such as cultivars resistant to diseases. In recent years, the Asian rust fungus (Phakopsora pachyrhizi Syd. & P. Syd 1914) has caused severe yield losses and the development of resistant cultivars is the best means of control. Understanding the genetic control and estimating parameters associated with soybean (Glycine max) resistance to P. pachyrhizi will provide essential information for cultivar selection. We investigated quantitative genetic control of P. pachyrhizi and estimated parameters associated to soybean yield in the absence and presence of this phytopathogen. Six cultivars and their 15 diallel derived F 2 and F 3 generations were assessed in experiments carried out in the absence and presence of P. pachyrhizi. The results indicated that soybean yield in the presence and absence of P. pachyrhizi is controlled by polygenes expressing predominantly additive effects that can be selected to develop new cultivars resistant or tolerant to P. pachyrhizi. These cultivars may prove to be a useful and more durable alternative than cultivars carrying major resistance genes.

-The objective of this work was to investigate the genotype-environment interaction in Mato Grosso State, MT. The relative importance of locations, years, sowing dates and cultivars and their interactions was analyzed from data collected in regional yield trials performed in a randomized complete block design with four replications, from 1994-1995 through 1999-2000, in Locations are relatively more important than years for yield testing soybeans in the MT State, therefore, investment should be made in increasing locations rather than years to improve experimental precision. Partitioning the MT State into regions has little impact on soybean yield testing results and, consequently, on the efficiency of the soybean breeding program in the State. Breeding genotypes with broad adaptation for the MT State is an efficient strategy for cultivar development.

The aim of this work was to perform genetic control on differential cultivars Michelite, Michigan Dark Red Kidney, Perry Marrow, Cornell 49-242, PI 207262, AB 136 and G 2333