José Francisco Ferraz de Toledo

Meiotic behavior of several Brazilian soybean varieties.

Despite the importance of soybeans little cytogenetic work has traditionally been done, due to the small size and apparent similarity of the chromosomes. Fifteen soybean [Glycine max (L.) Merrill] varieties adapted for cultivation in two distinct regions of Brazil were analyzed cytogenetically. A low frequency of meiotic abnormalities was noted in all varieties, although they were not equally affected. Irregular chromosome segregation, chromosome stickiness, cytoplasmic connections between cells, cytomixis and irregular spindles were the main abnormalities observed, none of which had been described previously in soybeans. All of these abnormalities can affect pollen fertility. Pollen fertility was high in most varieties and was correlated with meiotic abnormalities. Although soybean is not a model system for cytological studies, we found that it is possible to conduct cytogenetic studies on this species, though some modifications in the standard methods for meiotic studies were necessary to obtain satisfactory results.

Proposta de classificação dos coeficientes de variação em relação à produtividade e altura da planta de soja

The objective of this work was to define categories for the coefficients of variation obtained in soybean plant height and yield. The experimental data were obtained in intermediary and final (regional) adaptation trials carried out in the States of Parana and Mato Grosso. Different categories were established for each State and maturity group. Taking the mean and the standard deviation of the coefficients of variation obtained from the analyses of variance of the experiments, the coefficients of variation were classified as low, average, high and very high. An additional classification was made using the median and pseudo-sigma as substitutes for mean and standard deviation, respectively. The classification for the coefficients of variation depended on the trait and the location but did not vary greatly for each maturity group. The adopted criteria (mean and standard deviation or median and pseudo-sigma) were similar (regardless of the coefficient of variation distribution), and satisfactory in determining the experimental accuracy. The maximum acceptable limits for coefficient of variation are 16% and 12% for yield and plant height, respectively.

New soybean (Glycine max Fabales, Fabaceae) sources of qualitative genetic resistance to Asian soybean rust caused by Phakopsora pachyrhizi (Uredinales, Phakopsoraceae)

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 May 2001. Primary efforts to combat the disease involve the development of resistant cultivars, and four dominant major genes (Rpp1, Rpp2, Rpp3 and Rpp4) controlling resistance to ASR have been reported in the literature. To develop new long-lasting soybean ASR resistance genes, we used field experiments to assess ASR leaf lesion type in 11 soybean genotypes (BR01-18437, BRS 184, BRS 231, BRS 232, BRSGO Chapadoes, DM 339, Embrapa 48, PI 200487, PI 230970, PI 459025-A and PI 200526) and the 55 F2 generations derived from their biparental diallel crosses. The results indicated that PI 200487 and PI 200526 carry different dominant resistance major genes which are both different from Rpp2 through Rpp4. Furthermore, resistance to ASR in BR01-18437 is controlled by a single recessive major gene, also different from Rpp1 through Rpp4 and different from the genes in PI 200487 and PI 200526.

New genes conferring resistance to Asian soybean rust: allelic testing for the Rpp2 and Rpp4 loci

The objective of this study was to conduct allelic tests including crosses between a group of rust resistant genotypes from Embrapas soybean germplasm collection and PI 230970 and PI 459025, which carry the Rpp2 and Rpp4 genes, respectively. Asian Soybean rust (ASR) caused by the fungus Phakopsora pachyrhizi has resulted in significant yield losses and concern among Brazilian farmers. Until recently, there were four resistance genes (Rpp1 through Rpp4) described in the literature, but only Rpp2 and Rpp4 are still effective in Brazil. Twenty-six sources of resistance to P. pachyrhizi were crossed with PI 230970 and PI 459025 (Rpp2 and Rpp4 gene sources, respectively) and plants of their F2 generations were infected with a suspension containing 2.5x104 spores per milliliter and assessed in a greenhouse after 20 days, for the presence of resistant (RB) or susceptible (TAN) lesions. Chi-square tests were applied to investigate the hypotheses of independent or allelic resistance gene segregations. ASR resistant genes derived from PI 197182, PI 230971 and PI 417125 did not segregate in crosses with PI 230970, which indicates that these genotypes have a single resistance gene in the Rpp2 locus. Crosses with the other 23 genotypes resulted in segregating populations, suggesting that their resistance genes do not belong to Rpp2 or Rpp4 loci.

Interação genótipo x ambiente no desempenho produtivo da soja no Paraná

Os objetivos deste trabalho foram conhecer o grau de representatividade dos locais no Estado do Parana, onde sao conduzidos os ensaios de avaliacao final de produtividade de linhagens de soja no periodo 1990/2000 e realizar estudo de adaptabilidade e estabilidade das linhagens no ano agricola 1999/2000. As linhagens testadas pertencem aos grupos de maturacao precoce, semiprecoce e medio. Verificaram-se padroes de similaridade de resposta das linhagens dos tres grupos de maturacao, em alguns locais, em todos ou na maioria dos anos testados. Esses padroes dependeram do grupo de maturacao. Contudo, as avaliacoes em Londrina/Cambe, Campo Mourao, Guarapuava/Mariopolis e Sertaneja foram sempre indicadas. O local Ponta Grossa - 1 foi util na discriminacao de linhagens do grupo precoce, e Ponta Grossa - 2, dos grupos semiprecoce e medio. O estudo de adaptabilidade e estabilidade revelou que as linhagens precoces BR95-7613, BRS 137, OC95-3006 e CD96-518 tiveram bom desempenho produtivo, adaptabilidade geral e previsibilidade. A linhagem semiprecoce BR96-25619 mostrou a maior produtividade, tanto em ambientes favoraveis como nos desfavoraveis, e pode ser indicada como tendo adaptabilidade geral. Outras linhagens semiprecoces de bom desempenho, como BR96-18710 e BRS 154, sao indicadas para ambientes favoraveis e geral (ambientes favoraveis e desfavoraveis), respectivamente. As linhagens OC95-3194, BR96-12086 e BR96-16185, do grupo de maturacao medio, destacam-se nos ambientes favoraveis e desfavoraveis.

Interação genótipo-ambiente de soja convencional e transgênica resistente a glifosato, no Estado do Paraná

Os objetivos deste trabalho foram: comparar a produtividade e a adaptacao de genotipos de soja convencional e de soja transgenica resistente ao herbicida glifosato, de diferentes grupos de maturacao, desenvolvidos pelo programa de melhoramento da Embrapa Soja para o Estado do Parana; estudar a importância relativa dos efeitos de local, ano, cultivar e suas respectivas interacoes; e verificar a possibilidade de se estratificar o Estado em regioes mais homogeneas, para reduzir o numero de locais nos ensaios de competicao de linhagens. Foram utilizados dados de produtividade de graos de ensaios regionais, no Estado do Parana, entre 2001 e 2005. O delineamento experimental utilizado foi o de blocos ao acaso. A possibilidade de se realizar a estratificacao do Estado em regioes mais homogeneas e de descarte de locais foi verificada pela significância da interacao genotipo x ambiente entre locais. Nao houve diferenca significativa de produtividade entre a soja convencional e a transgenica, independentemente do grupo de maturacao. O efeito de local foi mais importante que o efeito de ano, na composicao dos ambientes. A estratificacao do Estado do Parana em regioes nao trouxe vantagens, nos anos analisados, para os testes de linhagens; apenas os locais da regiao Sul mostraram algum grau de similaridade entre si.

Genetic analysis of seed morphological traits and its correlations with Grain yield in common bean

This work investigated the genetic control of seed morphological traits and its correlations with grain yield in common bean. Three crossings among bean cultivars with different growth habit and seed characteristics were analyzed. F1 progenies gave origin to F2, RC1P1F1 and RC1P2F1 generations. Random samples of seeds from F2 generations and parents, F1 and backcrossings were sown during the season 2003/2004. Plant grain yield and seed morphological traits were determined by a sample of 150 plants from F2 generations and 20 plants from parents, F1 and backcrosssings. Genetic effects involved in each crossing were obtained from estimates of genetic components means and genetic and environmental components of phenotypical variance. Results showed that the seed morphological traits were controlled by a complex of genes, with additive effects predominance although dominance effects were present. High and negative correlations among seed length and thickness with grain yield suggested greater grain yield in bean plants with smaller seeds.

Interferência da interação genótipos x ambientes no controle genético da resistência à ferrugem asiática da soja

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 F1 generation was obtained in a greenhouse from crosses between five 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 F2 and F3 populations) in 2006/2007 and 2007/2008, in an experimental field 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 significant, did not alter the genetic parameters general combining ability (GCA) and specific 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.

Genetic control of soybean (Glycine max) yield in the absence and presence of the Asian rust fungus (Phakopsora pachyrhizi)

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 F2 and F3 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.

Genetic control in soybean of resistance to soybean cyst nematode race 4

Race 4+ refers to a population of soybean cyst nematode (SCN), Heterodera glycines, identified for the first time in Brazil, which differs from the classic race 4 for its ability to infect the cv. Hartwig, but not its ancestor PI 437654. Studies were carried out at Embrapa Soybean in Londrina, PR State, Brazil. Resistant genotypes E97-2502-9-3-1 and E97-2502-9-3-5 (types PI 437654) were crossed to the susceptible parent E96-776 (type ‘Hartwig’) to obtain 20 F1 plants, 120 F2 plants and 120 F2:3 families. The greenhouse trials involved those generations plus 20 plants of each parental genotype. Seedlings of each generation and of the race-differential cultivars were transplanted to clay pots and inoculated with 4000 eggs. After 28 days, the root system of each plant was washed and the females collected and counted. The inoculations resulted in high numbers of females in the susceptible genotypes in both crosses, confirming the presence of race 4+. The genetic analysis revealed no reciprocal cross effects, but some transgressive segregation with partial dominance toward resistance, and heritability estimates of medium to high magnitude. Resistant control in cross E96-776 × E97-2502-9-3-1 involved expression of additive, dominant and additive × additive epistatic effects, which suggests the presence of at least two genes. A single-gene hypothesis sufficed to explain the observed segregation in the E96-776 × E97-2502-9-3-5 cross with a simple additive-dominant model showing good fit to the data. The i-locus (expressing black seedcoat color) was associated with resistance.