Carlos Alberto Arrabal Arias

Molecular mapping of two loci that confer resistance to Asian rust in soybean.

Asian soybean rust (ASR) is caused by the fungal pathogen Phakopsora pachyrhizi Sydow & Sydow. It was first identified in Brazil in 2001 and quickly infected soybean areas in several countries in South America. Primary efforts to combat this disease must involve the development of resistant cultivars. Four distinct genes that confer resistance against ASR have been reported: Rpp1, Rpp2, Rpp3, and Rpp4. However, no cultivar carrying any of those resistance loci has been released. The main objective of this study was to genetically map Rpp2 and Rpp4 resistance genes. Two F2:3 populations, derived from the crosses between the resistant lines PI 230970 (Rpp2), PI 459025 (Rpp4) and the susceptible cultivar BRS 184, were used in this study. The mapping populations and parental lines were inoculated with a field isolate of P. pachyrhizi and evaluated for lesion type as resistant (RB lesions) or susceptible (TAN lesions). The mapping populations were screened with SSR markers, using the bulk segregant analysis (BSA) to expedite the identification of linked markers. Both resistance genes showed an expected segregation ratio for a dominant trait. This study allowed mapping Rpp2 and Rpp4 loci on the linkage groups J and G, respectively. The associated markers will be of great value on marker assisted selection for this trait.

Genotypic diversity among brazilian isolates of Macrophomina phaseolina revealed by RAPD

Macrophomina phaseolina has been considered one of the most prevalent soybean (Glycine max) pathogens in Brazil. No genetic resistance has been determined in soybean and very little is known about the genetic diversity of this pathogen in tropical and sub-tropical regions. Fifty-five isolates from soybean roots were collected in different regions and analyzed through RAPD for genetic diversity. The UPGMA cluster analysis for 74 loci scored permitted identification of three divergent groups with an average similarity of 99%, 92% and 88%, respectively. The three groups corresponded to 5.45%, 59.95% and 34.6%, respectively of all isolates used. A single plant had three different haplotypes, while 10.9% of the analyzed plants had two different haplotypes. In another study the genetic similarity was evaluated among isolates from different hosts [soybean, sorghum (Sorghum bicolor), sunflower (Helianthus annuus), cowpea (Vigna unguiculata), corn (Zea mays) and wheat (Triticum aestivum)] as well as two soil samples from native areas. Results showed that more divergent isolates originated from areas with a single crop. Isolates from areas with crop rotation were less divergent, showing high similarity values and consequently formed the largest group. Amplification of the ITS region using primers ITS1 and ITS4 produced only one DNA fragment of 620 bp. None of the isolates were differentiated through PCR-RFLP. Our results demonstrated genetic variability among Brazilian isolates of M. phaseolina and showed that one single root can harbor more than one haplotype. Moreover, cultivation with crop rotation tends to induce less specialization of the pathogen isolates. Knowledge of this variation may be useful in screening soybean genotypes for resistance to charcoal rot.

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.

Genetic similarity among soybean (Glycine max (L) Merrill) cultivars released in Brazil using AFLP markers

Genetic similarity among soybean genotypes was studied by applying the amplified fragment length polymorphism (AFLP) technique to 317 soybean cultivars released in Brazil from 1962 to 1998. Genetic similarity (GS) coefficients were estimated using the coefficient of Nei and Li (Nei and Li 1979), and the cultivars were clustered using the unweighted pair-group method with averages (UPGMA). The parentage coefficients of 100 cultivars released between 1984 and 1998 were calculated and correlated with the genetic similarity obtained by the markers. The genetic similarity coefficients varied from 0.17 to 0.97 (x = 0.61), with 56.8% of the coefficients being above 0.60 and only 9.7% equal to or less than 0.50. The similarity coefficients have remained constant during the last three decades. Dendrogram interpretation was hindered by the large number of cultivars used, but it was possible to detect groups of cultivars formed as expected from their genealogy. Another dendrogram, composed of 63 cultivars, allowed a better interpretation of the groups. Parentage coefficients among the 100 cultivars varied from zero to one (x = 0.21). However, no significant correlation (r = 0.12) was detected among the parentage coefficients and the AFLP genetic similarity. The results show the efficiency of AFLP markers in large scale studies of genetic similarity and are discussed in relation to soybean breeding in Brazil.

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.

Genetics of Nodulation and Nitrogen Fixation in Brazilian Soybean Cultivars

Abstract. The objective of this work was to study the genetics of the nodulation and biological nitrogen fixation (BNF) characteristics of Brazilian soybean cultivars. Four cultivars were identified with different capacities for BNF: J-200 and Bossier (high), Embrapa 20 (medium) and Embrapa 133 (low), and all possible crosses, including reciprocals, were carried out to obtain the F1, F2 and F3 generations. Three experiments were performed simultaneously, under greenhouse conditions, with the restricted set of generations P1, P2, F2 and F3, and plants were evaluated for nodulation (nodule number, NN, and nodule dry weight, NDW) and plant growth (shoot dry weight, SDW). No significant differences between reciprocal and direct effects were observed, therefore all data from F2, as well as from F3 plants were pooled. The frequency distributions for the tested variables in the F3 families were normal, with no evidences of discontinuities, consistent with polygenic inheritance. In the J-200 × Embrapa 133 and Bossier × Embrapa 133 crosses, the significance of the models for means and variances was less frequent, but was eventually observed for NN and NDW. In the other two experiments, there was a predominance of genetic additive (d) and/or genetic additive variance (D) effects for most of the tested variables, except for NDW in the cross of J-200 × Bossier. Genetic dominant effects (h) and/or genetic dominance variance (H) were detected for all variables in the cross Embrapa 20 × Embrapa 133 and for NDW/NN for Bossier × Embrapa 20. Additive × additive epistatic (i) and interaction genotype × microenvironment effects were less important in all experiments. The narrow-sense heritabilities (hn2) estimates ranged from 39% to 77%, with higher values for NN and NDW in Bossier × Embrapa 20 and for SDW in Embrapa 20 × Embrapa 133; these were high values when compared to other legumes. The prediction of the genetic potential to generate superior inbred lines for nodulation and BNF capacity indicated that selection could be more effective for crosses Bossier × Embrapa 20, and Embrapa 20 × Embrapa 133.

Main Stem and Tiller Contribution to Wheat Cultivars Yield Under Different Irrigation Regimes

No presente trabalho, determinou-se a contribuicao dos afilhos e perfilhos na produtividade total de dois cultivares de trigo (Triticum aestivum L.), Cocoraque e BH-1146, submetidos a dois regimes hidricos, um exposto as condicoes normais de campo e outro sobre regime de irrigacao, em Londrina, PR, Brasil. Utilizou-se o delineamento blocos completamente casualizados, com parcelas subdivididas, com oito repeticoes. As caracteristicas avaliadas foram produtividade total de graos, produtividade de graos dos afilhos e perfilhos, relacao da produtividade de graos dos perfilhos pela produtividade total de graos, componentes de produtividade e outros dezessete caracteres. Os resultados mostraram que o cultivar BH-1146 apresentou maior produtividade total de graos, em condicoes de deficit hidrico, em relacao ao cultivar Cocoraque. A produtividade dos afilhos respondeu positiva e significativamente a irrigacao, sendo esta a principal causa do aumento de produtividade dos dois cultivares testados. A produtividade de graos dos perfilhos pouco representou na produtividade total de graos.

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.