Romeu Afonso de Souza Kiihl

Molecular mapping of soybean rust ( Phakopsora pachyrhizi ) resistance genes: discovery of a novel locus and alleles

Soybean production in South and North America has recently been threatened by the widespread dissemination of soybean rust (SBR) caused by the fungus Phakopsora pachyrhizi. Currently, chemical spray containing fungicides is the only effective method to control the disease. This strategy increases production costs and exposes the environment to higher levels of fungicides. As a first step towards the development of SBR resistant cultivars, we studied the genetic basis of SBR resistance in five F2 populations derived from crossing the Brazilian-adapted susceptible cultivar CD 208 to each of five different plant introductions (PI 200487, PI 200526, PI 230970, PI 459025, PI 471904) carrying SBR-resistant genes (Rpp). Molecular mapping of SBR-resistance genes was performed in three of these PIs (PI 459025, PI 200526, PI 471904), and also in two other PIs (PI 200456 and 224270). The strategy mapped two genes present in PI 230970 and PI 459025, the original sources of Rpp2 and Rpp4, to linkage groups (LG) J and G, respectively. A new SBR resistance locus, rpp5 was mapped in the LG-N. Together, the genetic and molecular analysis suggested multiple alleles or closely linked genes that govern SBR resistance in soybean.

Identification of a new major QTL associated with resistance to soybean cyst nematode (Heterodera glycines)

Abstract Resistance of soybean [Glycine max (L.) Merr.] to cyst nematode (SCN) (Heterodera glycines Ichinohe), one of the most destructive pathogens affecting soybean, involves a complex genetic system. The identification of QTLs associated with SCN resistance may contribute to the understanding of such system. The objective of this work was to identify and map QTLs for resistance to SCN Race 14 with the aid of molecular markers. BC3F2:3 and F2:3 populations, both derived from an original cross between resistant cv. Hartwig and the susceptible line BR-92–31983 were screened for resistance to SCN Race 14. Four microsatellite (Satt082, Sat_001, Satt574 and Satt301) and four RAPD markers (OPAA-11795, OPAE-08837, OPR-07548 and OPY-072030) were identified in the BC3F2:3 population using the bulked segregant analysis (BSA) technique. These markers were amplified in 183 F2:3 families and mapped to a locus that accounts for more than 40% of the resistance to SCN Race 14. Selection efficiency based on these markers was similar to that obtained with the conventional method. In the case of the microsalellite markers, which identify homozygous resistant genotypes, the efficiency was even higher. This new QTL has been mapped to the soybean linkage group D2 and, in conjunction with other QTLs already identified for SCN resistance, will certainly contribute to our understanding of the genetic basis of resistance of this important disease in soybean.

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.

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.

Análise multivariada dos componentes da resistência à ferrugem-asiática em genótipos de soja

The objective of this study was to detail the infection cycles of Phakopsora pachyrhizi Syd. & P. Syd. in soybean genotypes, in order to establish a group of the most promising genotypes for use as sources of resistance to Asian soybean rust. The infection cycle components were quantifi ed in 48 genotypes. The assessments consisted of: type of lesion, intensity of sporulation, severity, number of lesions and uredinias, and productivity of urediniospores. The cluster analysis formed four groups: A - developed the highest amount of disease; B - developed the lowest amount of disease; C - low initial resistance; and D - high initial resistance. All the genotypes of groups B, C and D had RB (redish-brown) lesions and varied for initial resistance, delayed resistance, intensity of sporulation, stability of the qualitative response, productivity of urediniospores, and number of days to reach 50% of the maximum severity. Qualitative responses and disease severity evaluations refl ect the combined effects of resistance on all the infection components and show practical importance in genotypes differentiation, regarding disease resistance. The genotypes of groups B, C and D presented qualitative and quantitative resistance, in different degrees, and they are promising genotypes as sources of resistance to Asian soybean rust.

Inheritance of resistance to Soybean mosaic virus in FT-10 soybean

The occurrence of a new isolate from the G5 strain of Soybean mosaic virus (SMV), which broke the resistance of soybean cultivar FT-10, was first reported in Brazil in 1995. Cultivar Davis is an ancestor of ‘FT-10’ and the likely source of resistance to the virus. Diallel crosses among resistant cultivars Epps (PI 96983), Ogden and FT-10, and susceptible cultivar Hill were made to investigate the inheritance of SMV resistance in FT-10. The experiments for genetic studies were performed undergreen house conditions. Plants of the F2 population and F3 families from each cross and the parents were inoculated with SMV G1 and G5 strains. Plants were classified as: symptom less (R), susceptible with typical symptoms of mosaic (S), and systemic necrosis (N). Plants showing necrosis or no symptoms were classified as resistant. Each F3 family was classified as resistant (homozygous),susceptible (homozygous), or segregating (heterozygous). The results of both F2 and F3 were analyzed by Chi-square tests. The results suggested that FT-10 carries an allele at the Rsv1 locus for resistance to SMV. However, the allele is different from those in Epps and Ogden. The symbol Rsv1d is a tentatively named for the newly detected allele in FT-10. This allele probably originated from Davis cultivar.

Marcadores RAPD para detecção de resistência à ferrugem-asiática-da-soja

The objectives of this work were to confirm the PI 459025 inheritance of resistance (Rpp4) to Asian soybean rust pathogen and to detect RAPD markers linked to this resistance gene in soybean populations. Through the cross of the distint parental lines PI 459025 x Coodetec 208, a population was obtained, whose F2 and F2:3 generations had their populations artificially infected and evaluated for the reaction to Phakopsora pachyrhizi, by lesion type classification (RB - resistant and TAN - susceptible). Using the phenotypic results, the bulked segregant analysis was performed and two DNA bulks were obtained from homozygous resistant and homozygous susceptible plants, respectively. Out of the 600 random RAPD primers analyzed, three were identified as polymorphic fragments related to resistance, between contrasting bulks and parents. Through chi-square test, confirmations were obtained for the monogenic inheritance, with complete dominance segregation for resistance to the pathogen, and the 3:1 segregation of band presence for the markers. The three markers are linked to the resistance locus, in repulsion phase, at 5.1, 6.3 and 14.7 cM from it, in the linkage group G, which was confirmed by using the microsatellite marker Satt288. These makers are promising in assisted selection for Asian soybean rust resistance.

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.

BRS Celeste: nova cultivar de soja para o sistema de produção de grãos no cerrado

Maintenance or improvement of technology to soybean cultivation is necessary to reach economical productivity in the Brazilian Savannah, where it has shown to be superior to that obtained in the South of Brazil. New cultivars are among the contributions of research to high crop performance and yield stability. The soybean cv. BRS Celeste is an alternative to suit growers demand. It belongs to the same maturity group of cv. BR/EMGOPA 314 (Garca Branca), although it has higher yielding and shows resistance to the main diseases, especially stem canker (Diaporthe phaseolorum f. sp. meridionalis).

Chemical control and responses of susceptible and resistant soybean cultivars to the progress of soybean rust

This work compared development of soybean rust (SR) on the susceptible cultivar BRS 133 and on the resistant line CB06-953/963 (Rpp4 gene) following different fungicide treatments applied in different developmental stages. The assessed variables were percent plant defoliation, coefficient of damage (CD) and economic threshold level (ETL), the latter two calculated from disease severity ratings and yield. Experiments were conducted in the field during the 2006-2007 growing season with one sowing date (Experiment I) and in 2007-2008 with two sowing dates (Experiments II and III). The experimental design was a randomized complete block with ten treatments and four replications. Overall, the Rpp4 gene in the resistant line was effective in reducing development of SR in all three experiments. The values of CD and ETL were higher for the resistant line than for the susceptible cultivar. The resistant line needed 13.3 days longer than the susceptible cultivar to reach the ETL in Experiment II. Fungicide applications were more effective in protecting yield and minimizing defoliation in the susceptible cultivar than in the resistant line. Under high inoculum pressure (Experiment III), three and four fungicide sprays applied during the season resulted in significantly higher yields (P<0.05) in both soybean genotypes compared with the untreated controls. Late season fungicide applications reduced rust severity and increased the yield of the resistant cultivar.