Fungicides have not been effective in controlling the wheat blast disease in Brazil. An earlier analysis of 179 isolates of Pyricularia oryzae Triticum lineage (PoTl) sampled from wheat fields across six populations in central‐southern Brazil during 2012 discovered a high level of resistance to strobilurin fungicides. Here we analysed azole resistance in the same strains based on EC50 measurements for tebuconazole and epoxiconazole. All six Brazilian populations of PoTl exhibited high resistance to both azoles, with in vitro EC50 values that were at least 35 to 50 times higher than the recommended field doses. We sequenced the CYP51A and CYP51B genes to determine if they were likely to play a role in the observed azole resistance. Although we found five distinct haplotypes in PoTl carrying four nonsynonymous substitutions in CYP51A, none of these substitutions were correlated with elevated EC50. CYP51B was sequenced for nine PoTl isolates, three each representing low, medium, and high tebuconazole EC50. Both PoTl CYP51A and CYP51B could complement yeast CYP51 function. All PoTl CYP51A‐expressing yeast transformants were less sensitive to triazoles than the PoTl CYP51B ones. Transformants expressing PoTl CYP51A haplotype H1 carrying the R158K substitution were not more resistant than those expressing PoTl CYP51A haplotype H5, which is synonymous to haplotype H6, found in triazole‐sensitive P. oryzae Oryza isolates from rice blast. Therefore, the reduced triazole sensitivity of wheat blast isolates compared to rice blast isolates appears to be associated with a non‐target‐site related resistance mechanism acquired after higher exposure to triazoles.

Leaf blight, sheath blight, and web blight are major diseases caused by Rhizoctonia species on both Fabaceae and Poaceae plant hosts in the Brazilian Amazon agroecosystem. To determine the diversity of Rhizoctonia species associated with foliar diseases on fabaceous (cowpea and soybean) and poaceous (rice and signal grass [Urochloa brizantha]) hosts, a broad survey was conducted in Pará, Rondônia, Roraima, and Mato Grosso, in the Amazon, from 2012 to 2013. We extended our survey to Cerrado areas of Mato Grosso, and the lowlands of Paraíba Valley, in São Paulo, where these Rhizoctonia foliar diseases have not been reported so far. Our findings revealed that these diseases are caused by a diversity of Rhizoctonia solani AG‐1 complex. We detected that R. solani AG‐1 IA (sexual phase Thanatephorus cucumeris) was the predominant pathogen associated with signal grass leaf blight and collar rot diseases in the Amazon, especially in Rondônia and northern Mato Grosso. In addition, a subgroup of R. solani (AG‐1 IF), not previously reported in Brazil, was associated with leaf blight on cowpea and soybean, in Roraima. Another subgroup (AG‐1 ID) was also detected in Roraima. In Mato Grosso Cerrados we did not find any of the major Rhizoctonia foliar pathogens. Instead, R. oryzae (Waitea circinata) was the predominant species associated with a collar rot on U. brizantha. In the lowlands of São Paulo, R. oryzae‐sativae (Ceratobasidium oryzae‐sativae) was the predominant pathogen detected causing the rice sheath spot disease.

Wheat blast is one of the most important and devastating fungal diseases of wheat in South America, South‐east Asia, and now in southern Africa. The disease can reduce grain yield by up to 70% and is best controlled using integrated disease management strategies. The difficulty in disease management is compounded by the lack of durable host resistance and the ineffectiveness of fungicide sprays. New succinate dehydrogenase inhibitor (SDHI) fungicides were recently introduced for the management of wheat diseases. Brazilian field populations of the wheat blast pathogen Pyricularia oryzae Triticum lineage (PoTl) sampled from different geographical regions in 2012 and 2018 were shown to be resistant to both QoI (strobilurin) and DMI (azole) fungicides. The main objective of the current study was to determine the SDHI baseline sensitivity in these populations. Moderate levels of SDHI resistance were detected in five out of the six field populations sampled in 2012 and in most of the strains isolated in 2018. No association was found between target site mutations in the sdhB, sdhC, and sdhD genes and the levels of SDHI resistance, indicating that a pre‐existing resistance mechanism not associated with target site mutations is probably present in Brazilian wheat blast populations.

Populations of the soybean leaf blight pathogen (Rhizoctonia solani AG-1 IA) are highly genetically differentiated along a latitudinal gradient in the major soybean growing regions of Brazil. However, the evolutionary processes leading to regional adaptation are still unknown. The objective of this study was to evaluate the relative importance of neutral genetic variation and natural selection on the divergence and regional adaptation of populations of the soybean-infecting pathogen R. solani AG-1 IA. Therefore, we compared the phenotypic differentiation in quantitative traits (QST) and the neutral genetic differentiation (FST, based on microsatellites data) among three pairs of populations. As measures of phenotypic responses of the fungus (quantitative traits), we estimated the tolerance to temperature stress and the tolerance to a broad-spectrum fungicide (copper oxychloride) under optimal (25 °C) and high temperature conditions (33.5 °C). In general there was an increase in genetic variance with a positive effect on the heritability for tolerance to copper fungicide under temperature stress. The genetic differences among populations were the main determinants of thermal adaptation in R. solani AG-1 IA (h2 > 0.70). The analysis of neutral genetic structure (FST) indicated subdivision between the three pairs of populations. Although population pairwise comparisons between FST and QST values did not follow a single pattern, the majority of QST values did not differ significantly from FST, indicating that, for the quantitative characters studied, neutrality (or neutral evolution) had a major role in the regional adaptation of R. solani AG-1 IA populations.

Biological control is considered the only viable integrated disease management practice for controlling the widely distributed and destructive foliar blight and sudden death disease caused by the fungus Rhizoctonia solani AG-1 IA on signal grass (Urochloa brizantha) pastures. Since major signal grass varieties are highly susceptible and fungicide sprays are not labeled for grass pasture cropping systems, biological control is sought as an alternative for managing this fungal disease. In this study, 24 fluorescent Pseudomonas isolates obtained from naturally suppressive soils from the Amazon biome were bio-prospected for their role as biocontrol agents against R. solani AG-1 IA. Based on in vitro antagonism, three isolates (Amana, Poti, and Yara) were selected for further in vivo assays. Multilocus phylogenetic analysis indicated that Amana and Yara were grouped into the Pseudomonas putida group while Poti was grouped into the Pseudomonas asplenii group, and could well constitute a new Pseudomonas species. For in vivo biocontrol assays, the biocontrol agents were applied either via seed-treatment or via foliar spray. All three isolates produced siderophores and solubilized phosphate, while Amana and Poti showed protease and chitinase in vitro activity. Foliar application of P. putida Amana from Amazonian suppressive soils resulted in a significant reduction of the foliar blight disease severity on signal grass. We discuss further steps for the development and labeling of Pseudomonas-based biofungicides for managing the foliar blight disease on signal grass pastures in Brazil.

Espécies do gênero Rhizoctonia estão associadas ao complexo de manchas da bainha do arroz, sendo que R. oryzae-sativae, em particular, causa a mancha agregada da bainha. Neste estudo objetivou-se determinar o potencial adaptativo de duas populações de Rhizoctonia oryzae-sativae à cultura do milho, uma das culturas comerciais amplamente cultivadas no estado de São Paulo e que pode ser utilizada em rotação com o arroz irrigado. Não há relatos da doença em milho no Brasil. Foram inoculados, em plantas de milho, isolados de duas populações de R. oryzae-sativae e determinou-se componentes de evolucionabilidade ou do potencial adaptativo de uma população (i.e., medidas de resposta à seleção) como os coeficientes de variância genotípica (I ABSTRACTRhizoctonia species are associated with rice sheath-blight complex, and R. oryzae-sativae, in particular, causes aggregate sheath spot. This study aimed to determine the adaptive potential of two populations of R. oryzae-sativae to maize, one of the cash crops widely grown in São Paulo State and that could be used in rotation with irrigated rice. There is no report of the disease on maize in Brazil. Isolates of two populations of R. oryzae-sativae were inoculated in maize plants and components of evolvability or adaptive potential of a population (i.e., estimates of response to selection) were determined, such as genotypic variance coefficients (I O complexo de doenças das manchas e queimas da bainha do arroz está associado a fungos do gênero Rhizoctonia, sendo o fungo R. oryzae-sativae o agente causal da mancha agregada da bainha e o fungo R. solani AG-1 IA o patógeno da queima da bainha (1). Esse complexo de doenças vem se tornando importante nas regiões de cultivo de arroz, como na Califórnia e sudeste da Austrália, pois as perdas de rendimentos ocasionadas pela doença demonstraram uma potencial ameaça para as indústrias de processamento de arroz (17). No Brasil, os fungos R. oryzae-sativae e R. solani AG-1 IA foram relatados pela primeira vez como agentes causais das doenças da bainha em lavouras de arroz no interior do estado de São Paulo em 1967 e, em seguida, no Rio Grande do Sul em 1970 (1; 19). Além de fitopatógenos bastante destrutivos, fungos do gênero Rhizoctonia são organismos necrotróficos habitantes do solo, podendo sobreviver nas áreas de cultivo de arroz em restos de cultura e na forma de estruturas de resistência do tipo escleródios (30).Informação sobre a ocorrência e distribuição e importância relativa das espécies de Rhizoctonia que estão associadas ao complexo de manchas e queimas da bainha em arroz são de extrema relevância para o manejo da doença, que depende basicamente, da adoção de resistência varietal e do controle químico (19). Inerente a este fato, em estudos realizados na região do Vale do Paraíba, SP, detectou-se a prevalência de R. oryzae-sativae associado ao complexo de manchas da bainha do arroz, em 2013 (20).Desde o século XIX a região do Vale do Paraíba apresenta importância econômica na exploração agrícola, destacando-se na produção de a...

RESUMO Esta pesquisa propõe a utilização de um método baseado em leitor automatizado de microplacas para detectar resistência a fungicidas triazóis (IDM) e estrobirulinas (IQe) em populações do fungo hemibiotrófico fitopatogênico Pyricularia graminis-tritici (Pygt) do trigo. A disponibilidade de método acurado, mais rápido e eficiente para a detecção da redução da sensibilidade a fungicidas contribuiria para facilitar a tomada de decisão sobre o manejo químico da brusone do trigo no país. Há informação sobre redução da sensibilidade de triazóis no controle da brusone do trigo e evidências da ocorrência generalizada de redução da sensibilidade à estrobilurinas em populações do patógeno no Brasil. O método de microplaca foi acurado em discriminar a variação fenotípica na sensibilidade entre isolados do patógeno aos fungicidas IDM tebuconazol e epoxiconazol e ao fungicida IQe azoxistrobina. Economicamente, ambos os métodos representam alto custo, portanto, é necessário comparar a eficiência desses métodos. O método de microplacas foi mais eficiente no uso de recursos, com custo operacional total 33% inferior ao do método de placas de Petri. Em conjunto, os fatores acurácia, rapidez e eficiência no uso de recursos indicaram que o método de microplaca pode ser utilizado no monitoramento da resistência a fungicidas em populações do fungo da brusone do trigo no agroecossistema brasileiro.

RESUMO Muitos fitopatógenos de ampla distribuição geográfica como os fungos fitopatogênicos do gênero Rhizoctonia, estão sujeitos a extremas flutuações de temperatura em seus habitats. Para sobreviver a tais flutuações térmicas, esses organismos desenvolveram a habilidade de regular seus valores fenotípicos para adaptações térmicas bem como a outras variações ambientais específicas. O objetivo do presente estudo foi determinar o efeito do estresse térmico na evolucionabilidade para crescimento micelial de duas populações hospedeiro-distintas de Rhizocctonia solani AG-1 IA infectando arroz (OS6) ou Urochloa (BBT1) e compará-las a uma população de R. oryzae-sativae de arroz (OS5), espécie adaptada a temperaturas mais elevadas. As populações foram submetidas a duas temperaturas de crescimento: 25°C e 35°C (temperatura ótima e de estresse para R. solani AG-1 IA). Baseando-se em medidas do crescimento micelial, estimaram-se os coeficientes de variância genotípica (IG), variância ambiental (IE) e herdabilidade no sentido amplo (h2) como medidas de evolucionabilidade. Enquanto a população OS5 de R. oryzae-sativae foi pouco influenciada pelo estresse térmico, a 35oC detectou-se redução de h2 nas populações BBT1 e OS6 de R. solani AG-1 IA. Entretanto, os valores relativamente altos de h2 a 35oC (0,63 ± 0,07) indicaram que tanto a população BBT1 quanto a OS6 de R. solani AG-1 IA têm potencial de adaptação ao estresse térmico.