C. V. Godoy

Epidemics of Soybean Rust (Phakopsora pachyrhizi) in Brazil and Paraguay from 2001 to 2003

In 5 March 2001, a severe rust outbreak was recorded at Pitapó, Paraguay, and the causal organism was determined to be Phakopsora pachyrhizi using polymerase chain reaction (PCR) and DNA sequence analysis. In May, rust surveys showed spread throughout most of Paraguay and into western and northern Parana, Brazil. In the 2001-02 season, rust was widespread in Paraguay, but losses were reduced due to severe drought; however, in Brazil it spread to more than 60% of the soybean acreage, causing field losses estimated at 0.1 million metric tons (MMT). In 2003, the disease was observed in more than 90% of the fields in Brazil, and the projected losses in Mato Grosso and Bahia alone are 2.2 MMT (US

Distinct Biphasic mRNA Changes in Response to Asian Soybean Rust Infection

487.3 million). Approximately 80% of the soybean acreage in Brazil was sprayed twice with fungicides at the cost of US

Predicting severity of Asian soybean rust epidemics with empirical rainfall models

544 million. Differences in efficacy have been observed among the commercial strobilurin and triazol fungicides.

Efeitos Protetor, Curativo e Erradicante de Fungicidas no Controle da Ferrugem da Soja Causada por Phakopsora pachyrhizi, em Casa de Vegetação

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is now established in all major soybean-producing countries. Currently, there is little information about the molecular basis of ASR-soybean interactions, which will be needed to assist future efforts to develop effective resistance. Toward this end, abundance changes of soybean mRNAs were measured over a 7-day ASR infection time course in mock-inoculated and infected leaves of a soybean accession (PI230970) carrying the Rpp2 resistance gene and a susceptible genotype (Embrapa-48). The expression profiles of differentially expressed genes (ASR-infected compared with the mock-inoculated control) revealed a biphasic response to ASR in each genotype. Within the first 12 h after inoculation (hai), which corresponds to fungal germination and penetration of the epidermal cells, differential gene expression changes were evident in both genotypes. mRNA expression of these genes mostly returned to levels found in mock-inoculated plants by 24 hai. In the susceptible genotype, gene expression remained unaffected by rust infection until 96 hai, a time period when rapid fungal growth began. In contrast, gene expression in the resistant genotype diverged from the mock-inoculated control earlier, at 72 h, demonstrating that Rpp2-mediated defenses were initiated prior to this time. These data suggest that ASR initially induces a nonspecific response that is transient or is suppressed when early steps in colonization are completed in both soybean genotypes. The race-specific resistance phenotype of Rpp2 is manifested in massive gene expression changes after the initial response prior to the onset of rapid fungal growth that occurs in the susceptible genotype.

A new chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) affects Soybean Asian rust (Phakopsora pachyrhizi) spore germination

ABSTRACT Although Asian soybean rust occurs in a broad range of environmental conditions, the most explosive and severe epidemics have been reported in seasons with warm temperature and abundant moisture. Associations between weather and epidemics have been reported previously, but attempts to identify the major factors and model these relationships with field data have been limited to specific locations. Using data from 2002-03 to 2004-05 from 34 field experiments at 21 locations in Brazil that represented all major soybean production areas, we attempted to identify weather variables using a 1-month time window following disease detection to develop simple models to predict final disease severity. Four linear models were identified, and these models explained 85 to 93% of variation in disease severity. Temperature variables had lower correlation with disease severity compared with rainfall, and had minimal predictive value for final disease severity. A curvilinear relationship was observed between 1 month of accumulated rainfall and final disease severity, and a quadratic response model using this variable had the lowest prediction error. Linear response models using only rainfall or number of rainy days in the 1-month period tended to overestimate disease for severity <30%. The study highlights the importance of rainfall in influencing soybean rust epidemics in Brazil, as well as its potential use to provide quantitative risk assessments and seasonal forecasts for soybean rust, especially for regions where temperature is not a limiting factor for disease development.

Escala diagramática para avaliação da severidade da mancha alvo da soja

Protective, curative and eradicative effects of fungicides to control soybean rust caused by Phakopsora pachyrhizi, in greenhouse Protective, curative and eradicative effects of systemic fungicides (azoxystrobin 50 g a.i./ha + nimbus 0,5%, carbendazin 250 g a.i./ha, tebuconazole 100 g a.i./ha, difenoconazole 50 g a.i./ha e epoxiconazole 25 g a.i./ha + pyraclostrobin 66,5 g a.i./ha) were evaluated in soybean (Glycine max) plants inoculated with a urediniosporal suspension of Phakopsora pachyrhizi, in greenhouse. To evaluate the protective effect plants were treated with fungicides and inoculated four, eight and 14 days after the treatment. To evaluate the curative and eradicative effects, the plants were inoculated with a urediniosporal suspension of P. pachyrhizi and treated with fungicides after two, four and eight days. Disease severity was assessed 16 days after each inoculation. With the exception of the fungicide carbendazin, all of the fungicides inhibited over 90% of urediniosporal germination until eight days after the treatment. Plants inoculated 16 days after the treatment with carbendazin presented severity statistically similar to unsprayed plants, while plants treated with fungicides of ergosterol biosynthesis inhibitors and strobilurin groups showed over 60% germination control. None of the tested fungicides provided an eradicative effect when applied before symptoms developed. However, all treatments reduced disease severity and urediniosporal viability. With the exception of carbendazin, all fungicides inhibited over 60% of urediniosporal germination until eight days after inoculation, in the incubation period of the disease.

Eficiência do controle da ferrugem asiática da soja em função do momento de aplicação sob condições de epidemia em Londrina, PR

BackgroundAsian rust (Phakopsora pachyrhizi) is a common disease in Brazilian soybean fields and it is difficult to control. To identify a biochemical candidate with potential to combat this disease, a new chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) (CaclXIP) leaves was cloned into the pGAPZα-B vector for expression in Pichia pastoris.ResultsA cDNA encoding a chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) (CaclXIP), was isolated from leaves. The amino acid sequence predicts a (β/α)8 topology common to Class III Chitinases (glycoside hydrolase family 18 proteins; GH18), and shares similarity with other GH18 members, although it lacks the glutamic acid residue essential for catalysis, which is replaced by glutamine. CaclXIP was expressed as a recombinant protein in Pichia pastoris. Enzymatic assay showed that purified recombinant CaclXIP had only residual chitinolytic activity. However, it inhibited xylanases from Acrophialophora nainiana by approx. 60% when present at 12:1 (w/w) enzyme:inhibitor ratio. Additionally, CaclXIP at 1.5 μg/μL inhibited the germination of spores of Phakopsora pachyrhizi by 45%.ConclusionsOur data suggests that CaclXIP belongs to a class of naturally inactive chitinases that have evolved to act in plant cell defence as xylanase inhibitors. Its role on inhibiting germination of fungal spores makes it an eligible candidate gene for the control of Asian rust.

Avaliação da tolerância de cultivares de soja à ferrugem asiática no oeste da Bahia

A mancha alvo da soja, causada pelo fungo Corynespora cassiicola, e encontrada em praticamente todas as regioes de cultivo de soja do Brasil e pode causar perdas economicas. Esse trabalho teve como objetivo elaborar e validar uma escala diagramatica para avaliacao da severidade da mancha alvo da soja. Para tal, foram coletados foliolos de soja com sintomas da doenca, onde se mediu a severidade, determinando-se os limites minimos e maximos, e os niveis intermediarios da escala de acordo com a lei do estimulo visual de Weber-Fechner. A escala elaborada apresentou sete niveis de severidade: 1, 2, 5, 9, 19, 33 e 52%. A validacao foi realizada por oito avaliadores, sem experiencia em quantificar essa doenca, que estimaram a severidade de 40 foliolos com diferentes niveis de severidade da mancha alvo, sem e com o auxilio da escala. A utilizacao da escala diagramatica resultou em melhor acuracia e precisao das estimativas realizadas, sendo uma ferramenta de facil e rapida utilizacao, que pode ser adotada para auxiliar na avaliacao da severidade da mancha alvo da soja.

Models and applications for risk assessment and prediction of Asian soybean rust epidemics

Com o objetivo de estudar a eficiencia do controle da ferrugem asiatica da soja em funcao do momento de aplicacao foram conduzidos ensaios em Londrina, PR, Brasil, durante as safras 2005/06 e 2006/07. A mistura de 60 g azoxistrobina ha-1 + 24 g ciproconazol ha-1 foi aplicada em diferentes estadios fenologicos, iniciando em R2 ate R5.5, em aplicacoes unicas e sequenciais. A severidade foi estimada periodicamente para o calculo da area abaixo da curva de progresso da doenca (AACPD) e a produtividade avaliada no final do ciclo. Nas duas safras, os sintomas iniciais foram observados no final do estadio vegetativo. Na safra 2005/06, o tratamento com aplicacoes sequenciais, em R2 e R5.1, foi o mais eficiente na reducao da severidade e da AACPD e apresentou a maior produtividade. Na safra 2006/07, os tratamentos com aplicacoes sequenciais, em R2 e R5.1, e a aplicacao unica em R3 apresentaram as menores severidades, menores AACPD e maiores produtividades. Correlacoes negativas foram encontradas entre as variaveis severidade em R6 e AACPD e a produtividade (-0,83 e -0,84 em 2005/06 e -0,87 e -0,89 em 2006/07). As aplicacoes realizadas com niveis elevados de severidade, ao redor de 50%, apresentaram produtividade igual a testemunha nao tratada.

Ferrugem-asiática da soja no Brasil: passado, presente e futuro

Tolerance assessment of soybean cultivars to Asian rust caused by Phakopsora pachyrhizi in western Bahia The use of tolerance as a form of control for soybean rust can be a viable alternative, since qualitative resistance has been shown to be unstable in function of fungal variability. This trial was carried out at in western Bahia in 2003/04, with the objective of assessing the tolerance of the main soybean (Glycine max) cultivars used in the area. Four early maturity cultivars [MG/BR 46 (Conquista), Emgopa 315, BRS Corisco and M-SOY 8411] and four cultivars of late maturity (BRS Barreiras, M-SOY 9350, FT 106 and BRS Sambaiba) were assessed. Tolerance was quantified by determining the difference of yield in subplots treated and untreated with fungicide. The cultivars MG/BR 46 (Conquista) and M-SOY 8411 did not present significant yield differences; however, this could not be attributed to tolerance in function of the low severity observed in this trial. This difference could be attributed to escape, since when the rust obtained higher values of severity, the two cultivars were already in the final stages of development. Although the maximum severity observed in this trial has been low (30.5% for BRS Barreiras), except MG/BR 46 (Conquista) and MSOY 8411, the others cultivars assessed presented significant differences among the subplots treated and untreated with fungicide. This shows an absence of tolerance in the main cultivars commercially planted in western Bahia. It was observed that early maturity cultivars had inferior yield reductions than late maturity cultivars. Additional keywords: resistance, control, Glycine max.