Cercospora leaf blight and purple seed stain are caused by Cercospora kikuchii and other Cercospora spp. The fungus can infect leaves and seeds on soybean, and the disease is controlled with fungicides. In Brazil, the intensive use of fungicides on soybean to control other diseases such as soybean rust has exerted resistance selection pressure on all fungal pathogens that attack in the crop. In this study, we evaluated the sensitivity of 56 Cercospora spp. soybean isolates collected during 9 crop seasons in 9 Brazilian states to quinone outside inhibitors (QoI) and methyl benzimidazole carbamate (MBC) fungicides using mycelial growth inhibition in amended media with a discriminatory dose of 10 μg/mL. We also analyzed single polymorphisms in the target genes cytb and β-tubulin using target genotyping by sequencing by Illumina short reads. Genome-local association was used to correlate the point mutations found in the coding sequence with in vitro assays results. For cytb gene, it was observed only the G143A mutation in 73% of the isolates. The mutation G143A was present in 97% of the isolates classified as resistant at least for two QoI fungicides. The mutation E198A was present in 71% of the isolates being significantly associated with the reduction control to MBC fungicides. Cross-resistance was observed into QoI (azoxystrobin, picoxystrobin, and pyraclostrobin) and MBC (carbendazim, and thiophanate-methyl) active ingredients fungicides. About 97% of Cercospora spp. isolates analyzed possessed the double mutations G143A and E198A and resulting in less sensitive to QoI and MBC fungicides, respectively. All isolates showed homozygous variation in the alternative allele in G143A and E198A mutations. Our results suggest that resistance of the Cercospora spp. from soybean to QoI and MBC fungicides has occurred since the 2008 cropping season in Brazil associated with G143A and E198A mutations.

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Ramularia leaf spot is a disease of major importance on cotton fields in Brazil due to its effects on yield and cotton fiber quality. Two Ramulariopsis (syn. Ramularia) species, R. gossypii and R. pseudoglycines, are reported as the causal agents of this disease, but it is unknown which species is the most prevalent in Brazilian cotton fields. The goal of this work was to determine the most frequent species occurring on field samples from a molecular monitoring program which sampled from all cotton growing regions in Brazil from 2017 to 2020 seasons. We also used molecular tools for genotyping a region of the Cytb gene for all sampled isolates. Sequencing of an ITS-rDNA region was used for Ramulariopsis species determination, and a DNA fragment from the Cytb gene was amplified, sequenced, and analyzed for all 165 isolates. The ITS-rDNA sequencing confirmed that all isolates belong to the Ramulariopsis, and most notably, all the SNPs observed in this region, are of the R. pseudoglycines species for all 165 isolates, thus all analyzed isolates were assigned to this species. The analysis of the Cytb gene fragment sequenced showed the presence of the G143A substitution, and absence of G137R substitution, in all 165 isolates.

BACKGROUND Fungicides of the succinate dehydrogenase inhibitors (SDHIs) group have been used in soybean to control Asian soybean rust (ASR) caused by Phakopsora pachyrhizi. Fungal populations with less sensitivity to SDHI fungicides have been reported since 2015. RESULTS In this study, fungal sensitivity to benzovindiflupyr (BZV) and fluxapyroxad (FXD) was assessed using a total of 770 P. pachyrhizi populations sampled over four soybean growing seasons. Cross‐resistance, intrinsic activity, and frequency of SDHC‐I86F mutation were also analyzed. The average effective concentration to inhibit 50% (EC50) and SDHC‐I86F frequency increased over the 2015/2016, 2016/2017, 2017/2018 and 2018/2019 soybean‐seasons. Fourteen P. pachyrhizi populations had the EC50 value above 10 mg L−1 for both carboxamides. No difference was found in intrinsic active to BZV and FXD fungicides for sensitive P. pachyrhizi populations. For P. pachyrhizi classified as less sensitive BZV showed the highest fungitoxicity effect. High frequency of the C‐I86F mutation was observed in samples collected in volunteer soybean plants. The maximum frequency of SDHC‐I86F mutation in the population was 50% and resulting in ASR populations with low sensitivity to SDHIs. A low correlation between bioassay and SDHC‐I86F mutation was observed possible due to the dikaryotic nature of rust fungi or other mutations in the other succinate dehydrogenase subunits. CONCLUSION The present work provides an overview of a large sampling size of P. pachyrhizi populations and their performance over the four crop seasons. The high frequency of SDHC‐I86F mutation and low sensitivity to SDHIs are widely distributed in the main soybean growing regions in Brazil and present in volunteer plants in the soybean‐free period. Further detailed studies are needed to identify novel point mutations affecting the effectiveness of SDHIs. © 2021 Society of Chemical Industry.

A estimativa visual da severidade de doenças em plantas nem sempre se correlaciona com o efeito desta sobre a atividade fotossintética do hospedeiro. O objetivo do trabalho foi avaliar a interferência dos fungos Corynespora cassiicola e Erysiphe diffusa, causadores da mancha-alvo e do oídio na cultura da soja, respectivamente, na eficiência fotossintética de folhas infectadas. A fotossíntese foi relacionada com a área foliar doente por meio da equação Px/ Po=(1-x)β. Os parâmetros β (± erro padrão) estimados foram 2,78 (± 0,28) (p<0,05) para as folhas infectadas com C. cassiicola e 0,72 (±0,09) (p<0,05) e 0,77 (±0,15) (p=0,15) com E. diffusa, na primeira e segunda repetições. O valor obtido para C. cassiicola (β>1) indica que houve redução da eficiência fotossintética no tecido lesionado e em parte do tecido verde remanescente, enquanto que os valores obtidos para E. diffusa (β≤1) indicam que a estimativa visual da severidade da doença é um bom indicador do efeito do fungo na taxa fotossintética do hospedeiro.

Target spot on soybean (Glycine max), caused by the fungus Corynespora cassiicola, was first reported in Brazil in 1976 (Almeida et al., 1976). The disease was considered of minor importance for many years. Recently, the severity of the disease has been increasing, and it has now been reported in all Brazilian soybean-growing regions. Management strategies include seed treatment, crop rotation, the use of tolerant/resistant cultivars, and chemical control (Godoy et al., 2016). The disease has a significant effect on yield,

Drench applications of systemic acquired resistance (SAR) inducing compounds acibenzolar-s-methyl (ASM) and thiamethoxam (THIA) may contribute for the control of citrus canker, caused by Xanthomonas citri subsp. citri. Here, we report the results of a 3-year field experiment on the effect of drench applications of two SAR-inducing compounds, applied alone or in combination with copper oxychloride (CuOX) foliar sprays, on citrus canker control, as well as tree growth and yield, of Natal sweet orange trees under Brazilian subtropical conditions. Leaf disease incidence, tree defoliation, and citrus leaf miner (Phyllocnistis citrella) attack were evaluated every 30 days for 16 months. Soil applications of ASM or THIA combined with foliar sprays of CuOX highly reduced citrus canker incidence on leaves. Effective control of the disease, comparable to regular foliar sprays of cupric bactericides, was obtained with two to four drench applications of SAR-inducing compounds. No differences among the treatments were observed in regard to tree height and canopy volume, and fruit yield of the young citrus trees. Soil applications of SAR-inducing compounds proved to be an important measure for the integrate management of citrus canker under the Brazilian subtropical conditions. Keywords Systemic acquired resistance. Xanthomonas citri subsp. citri. Citrus leaf miner. Copper in bacterial disease management. Neonicotinoid insecticide

RESUMO O fungo Corynespora cassiicola, agente causal da mancha-alvo na soja, apresenta baixa esporulação em meios de cultura artificiais, o que dificulta a produção de esporos em condições de laboratório. O objetivo deste estudo foi avaliar a esporulação e o crescimento micelial radial de 21 isolados de C. cassiicola, obtidos de folhas de soja coletadas nas principais regiões produtoras do Brasil e submetidos a diferentes regimes de iluminação e estresse. Os isolados foram submetidos a três regimes de iluminação: luz contínua, 12 h/12 h de luz-escuro e escuro contínuo e duas condições de estresse mecânico: raspagem superficial da colônia ou ausência de estresse. A produção de esporos dos isolados foi quantificada utilizando um hemacitômetro, enquanto o crescimento micelial radial foi realizado pela média de dois diâmetros perpendiculares da colônia. A esporulação e o crescimento micelial radial sob diferentes regimes de iluminação e estresse, apresentaram comportamentos específicos para cada isolado. Não foi observada correlação significativa entre o crescimento micelial e a produção de esporos.