Soybean rust (SBR), caused by Phakopsora pachyrhizi Sydow, is one of the most economically important and destructive diseases of soybean [Glycine max (L.) Merr.] and the discovery of novel SBR resistance genes is needed because of virulence diversity in the pathogen. The objectives of this research were to map SBR resistance in plant introduction (PI) 561356 and to identify single nucleotide polymorphism (SNP) haplotypes within the region on soybean chromosome 18 where the SBR resistance gene Rpp1 maps. One-hundred F 2:3 lines derived from a cross between PI 561356 and the susceptible experimental line LD02-4485 were genotyped with genetic markers and phenotyped for resistance to P. pachyrhizi isolate ZM01-1. The segregation ratio of reddish brown versus tan lesion type in the population supported that resistance was controlled by a single dominant gene. The gene was mapped to a 1-cM region on soybean chromosome 18 corresponding to the same interval as Rpp1. A haplotype analysis of diverse germplasm across a 213-kb interval that included Rpp1 revealed 21 distinct haplotypes of which 4 were present among 5 SBR resistance sources that have a resistance gene in the Rpp1 region. Four major North American soybean ancestors belong to the same SNP haplotype as PI 561356 and seven belong to the same haplotype as PI 594538A, the Rpp1-b source. There were no North American soybean ancestors belonging to the SNP haplotypes found in PI 200492, the source of Rpp1, or PI 587886 and PI 587880A, additional sources with SBR resistance mapping to the Rpp1 region.

Resumo -O objetivo deste trabalho foi quantificar os efeitos da interação genótipo x ambiente (GxE) sobre a produtividade de grãos em progênies de soja pré-selecionadas para resistência à ferrugem asiática (Phakopsora pachyrhizi). Doze ensaios de avaliação de progênies (linhagens F 6 e F 7 ) foram conduzidos em diferentes ambientes (combinação de locais, anos e tratamentos fungicidas para controle de doenças de final de ciclo, incluindo ou não a ferrugem). A análise "additive main effects and multiplicative interaction" (AMMI) capturou, como padrão da interação GxE, 57% da variação associada aos resíduos de não aditividade, dos quais 44% foram retidos no primeiro componente principal de interação e o restante, no segundo. O primeiro componente associou-se a diferenças entre os anos de avaliação, o que denota imprevisibilidade na predição. O segundo componente, no entanto, associou-se ao manejo diferenciado do cultivo, no que se refere ao controle ou não das doenças. Entre os genótipos de ampla adaptabilidade produtiva, as linhagens USP 02-16.045 e USP 10-10 apresentaram desempenho destacado.Termos para indexação: Glycine max, Phakopsora pachyrhizi, biplot, interação genótipo x ambiente. AMMI analysis of grain yield in soybean lines selected for resistance to Asian rustAbstract -The objective of this work was to quantify the effects of genotype x environment (GxE) interaction on grain yield in soybean progenies pre-selected for resistance to Asian soybean rust (Phakopsora pachyrhizi). Twelve trials evaluating progenies (lines F 6 and F 7 ) were carried out in different environments (combination of locations, years, and fungicide treatments to control late season diseases, including or not rust). Additive main effects and multiplicative interaction (AMMI) analysis captured, as GxE interaction pattern, 57% of the variance associated with the residues of non-additivity, of which 44% were retained in the first principal component of interaction, and the remainder in the second. The first component was associated with the differences between the years of evaluation, which denotes unpredictability. The second component, however, was associated with different crop managements, related to the control or not of the diseases. Among genotypes with wide yield adaptability, the USP 02-16.045 and USP 10-10 lineages stood out.

Resumo -O objetivo deste trabalho foi detalhar os ciclos de infecção da Phakopsora pachyrhizi Syd. & P. Syd. em genótipos de soja, para o estabelecimento de grupos de genótipos mais promissores para o uso como fontes de resistência à ferrugem. Os componentes do ciclo de infecção foram quantifi cados em 48 genótipos. Foram avaliados: tipo de lesão, intensidade de esporulação, severidade, número de lesões e de urédias e produtividade de urediniósporos. Pela análise de agrupamentos, formaram-se quatro grupos: A -desenvolveu a maior quantidade de doença; B -desenvolveu a menor quantidade de doença; C -baixa resistência inicial e D -alta resistência inicial. Os genótipos dos grupos B, C e D apresentaram lesões RB ("redish-brown") e variaram quanto à resistência inicial, resistência tardia, intensidade de esporulação, estabilidade da resposta qualitativa, produtividade de urediniósporos e número de dias para atingir 50% da severidade máxima. Entre as variáveis analisadas, as que apresentaram importância prática foram as avaliações das respostas qualitativas e as de severidade. Esta última refl ete os efeitos combinados de resistência sobre todos os componentes da infecção e apresentam importância prática na diferenciação de genótipos, quanto à resistência à doença. Os genótipos dos grupos B, C e D manifestaram resistência qualitativa e quantitativa, em diferentes graus, e promissores para serem utilizados como fontes de genes de resistência à ferrugem-asiática-da-soja.Termos para indexação: Glycine max, Phakopsora pachyrhizi, epidemiologia, número de lesões, número de urédias, resistência horizontal e vertical, resistência quantitativa e qualitativa. Multivariate analysis of resistance components to Asian rust in soybean genotypesAbstract -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 res...

Soybean rust (SBR; caused by Phakopsora pachyrhizi Sydow) is a threat to soybean [Glycine max (L.) Merr.] production worldwide. Although SBR has not caused widespread damage in North America, the crop is still threatened by the disease because most cultivars in production are susceptible. We backcrossed the SBR‐resistance genes Rpp1, Rpp1‐b, Rpp?(Hyuuga), and Rpp5 into the maturity group (MG) II experimental line LD01‐7323 and the MG IV cultivar LD00‐3309 to develop Midwest‐adapted soybean germplasm with SBR resistance. The backcross lines were tested for SBR resistance in greenhouse tests and for agronomic traits in multilocation field tests. The four MG II soybean germplasm lines LD10‐30052 (Reg. No. GP‐383, PI 668384), LD10‐14321 (Reg. No. GP‐ 384, PI 668385), LD10‐14284 (Reg. No. GP‐ 385, PI 668386), and LD09‐16057 (Reg. No. GP‐ 386, PI 668387) and the four MG IV germplasm lines LD10‐14205 (Reg. No. GP‐ 389, PI 668390), LD10‐13091 (Reg. No. GP‐ 387, PI 668388), LD10‐14274 (Reg. No. GP‐ 388, PI 668389), and 08RST5‐10 (Reg. No. GP‐ 390, PI 668391) developed through these efforts were released by the Illinois Agricultural Experiment Station in April 2012. The lines carry SBR resistance genes and are indistinguishable from the recurrent parents for morphological traits and, with only a few exceptions, are not significantly different than their recurrent parents for agronomic traits including seed yield. These lines should be useful to soybean breeders who wish to develop rust‐resistant cultivars.

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