Eficacia de fungicidas para el control de manchas foliares en soja en el distrito de Minga Guazú, Paraguay

Las enfermedades son una de las mayores limitantes fitosanitarias en el cultivo de soja [Glycine max (L.) Merr.], entre ellas las enfermedades de final de ciclo (EFC) son las protagonistas en ausencia de la roya asiática de la soja (Phakopsora pachyrhizi). Este trabajo presenta los resultados de evaluaciones a campo de la eficacia de diferentes fungicidas en el control de las EFC en el cultivo de soja. El ensayo se realizó en Minga Guazú, Alto Paraná, Paraguay. Se utilizó la variedad NA 5909 RR. Los ingredientes activos evaluados fueron Bixafen + Protioconazole + Trifloxistrobin (T2), Picoxystrobin + Protioconazole (T3), Picoxystrobin + Cyproconazole (T4), Fluxapyroxad + Epoxiconazole + Pyraclostrobin (T5), (Benzovindiflupyr + Azoxistrobina) + Difenoconazole + Ciproconazole (T6), Mancozeb (T7) y Carbendazim (T8). Las aspersiones se realizaron según la ocurrencia de los estadios fenológicos R1, R3 y R5. Las principales variables evaluadas fueron la severidad, eficacia de control (EC) y rendimiento en kg ha1 . La menor severidad se observó con el T5, mientras que T8 no fue efectivo para reducir la severidad; los tratamientos T5, T6 y T2 fueron los más eficaces para controlar las EFC, diferenciándose significativamente de los demás tratamientos. Los tratamientos T2, T3, T4, T5, T6 y T7 obtuvieron los mejores rendimientos y fueron estadísticamente similares. El T8 mostró el menor rendimiento y peso de mil semillas. En conclusión, la mayoría de los fungicidas presentaron un buen control sobre las EFC, así también sobre el rendimiento de la soja.

Physics-informed deep learning characterizes morphodynamics of Asian soybean rust disease

Medicines and agricultural biocides are often discovered using large phenotypic screens across hundreds of compounds, where visible effects of whole organisms are compared to gauge efficacy and possible modes of action. However, such analysis is often limited to human-defined and static features. Here, we introduce a novel framework that can characterize shape changes (morphodynamics) for cell-drug interactions directly from images, and use it to interpret perturbed development of Phakopsora pachyrhizi, the Asian soybean rust crop pathogen. We describe population development over a 2D space of shapes (morphospace) using two models with condition-dependent parameters: a top-down Fokker-Planck model of diffusive development over Waddington-type landscapes, and a bottom-up model of tip growth. We discover a variety of landscapes, describing phenotype transitions during growth, and identify possible perturbations in the tip growth machinery that cause this variation. This demonstrates a widely-applicable integration of unsupervised learning and biophysical modeling.

Fungi Resistance to Multissite Fungicides

Multisite fungicides have been used for many years in fruit and vegetable crops worldwide. Cases of the fungi resistance development to these fungicides have been rare. From the 2002 season onwards, with the outbreak of Asian soybean rust in Brazil, caused by Phakopsora pachyrhizi, site-specific fungicides became the main weapon for its control. From 2002 to 2011, penetrant mobile site-specific fungicides were used and until today in double (DMI + QoI) or triple (DMI + QoI + SDHI) co-formulatoons in an area of more than 30 million hectares and with three sprays per area. This resulted, as expected, in the fungus sensitivity reduction, today with cross and multiple resistance to those site-specific fungicides. From the 2011 season in an attempt to recover control that for some chemicals and mixtures reached < 30%, research was started with site-specific + multi-site mixtures, taking as example Phytophthora infestans resistance development to metalaxyl in Europe showinig long-lasting solution found by the addition of multisite mancozeb. It is expected that the effective life of site-specific + multi-site mixtures may be as long in controlling soybean rust as it has been for potato, tomato and grape downy mildews. This review presents the concepts involved in the sensitivity reduction to fungicides. Some fungal species and fungicides involved are listed. Considering the P. pachyrhizi sporulation potential, the great soybean area sprayed and the number of sprays per area mainly with site-specific co-formulations and the reduced area sprayed with multisites, we discuss the need for annual monitoring of P. pachyrhizi sensitivity to the these chemicals.

Covering Soybean Leaves With Cellulose Nanofiber Changes Leaf Surface Hydrophobicity and Confers Resistance Against Phakopsora pachyrhizi

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi, an obligate biotrophic fungal pathogen, is the most devastating soybean production disease worldwide. Currently, timely fungicide application is the only means to control ASR in the field. We investigated cellulose nanofiber (CNF) application on ASR disease management. CNF-treated leaves showed reduced lesion number after P. pachyrhizi inoculation compared to control leaves, indicating that covering soybean leaves with CNF confers P. pachyrhizi resistance. We also demonstrated that formation of P. pachyrhizi appressoria, and also gene expression related to these formations, such as chitin synthases (CHSs), were significantly suppressed in CNF-treated soybean leaves compared to control leaves. Moreover, contact angle measurement revealed that CNF converts soybean leaf surface properties from hydrophobic to hydrophilic. These results suggest that CNF can change soybean leaf surface hydrophobicity, conferring resistance against P. pachyrhizi, based on the reduced expression of CHSs, as well as reduced formation of pre-infection structures. This is the first study to investigate CNF application to control field disease.

Virulence diversity of Phakopsora pachyrhizi in Mexico

Asian soybean rust (ASR), caused by the pathogen Phakopsora pachyrhizi, is the main disease of soybean in Mexico and worldwide, threatening its production. Knowledge about the virulence of Mexican rust populations (MRPs) is crucial in order to develop or introduce soybean cultivars with resistance to this disease. This study investigated the geographic variation on the virulence of 19 MRPs collected in two states of Mexico: Tamaulipas and Chiapas, using a set of 12 differential soybean varieties. The inoculation of MRPs showed that there was no large difference in virulence to differentials carrying Rpp4 or Rpp5 between MRPs from the two states. However, a contrasting phenotype was observed on Rpp1, Rpp1-b, Rpp2, and Rpp3. In the comparative analysis of virulence profiles with 157 and 20 P. pachyrhizi samples from South America and Asia, respectively, the MRPs from Chiapas form an isolated cluster, including the Tamaulipas state. The MRPs from Tamaulipas clustered with South American samples because of common characteristics, such as virulence to Rpp1 and avirulence to Rpp1-b. However, opposite reactions on Rpp1 and Rpp1-b that have been reported in major USA pathogen were also observed in Chiapas samples. A common trend between Chiapas and major USA pathogen was also observed in Rpp3. As the main conclusion of the present study, the 1,000 km distance between these two states in Mexico makes a big difference in the virulence of ASR.

USO DO BACILLUS SUBTILIS COMO AGENTE DE BIOCONTROLE DE FITOPATÓGENOS DA CULTURA DE SOJA

Atualmente a soja é uma das culturas de maior importância econômica para o Brasil e o mundo, sendo uma das principais fontes de renda nas exportações brasileiras. Um dos grandes desafios enfrentados pela sojicultura é o controle de patógenos causadores de doenças, dentre as quais a ferrugem, causada pelo fungo Phakopsora pachyrhizi, merece destaque devido a sua severidade, fácil dispersão e potencial de dano, podendo gerar perdas de até 90% na cultura. O controle de doenças como a ferrugem é feito, principalmente, através do uso de fungicidas, produtos de alta toxicidade que vem causando problemas ambientais e à saúde humana ao longo dos anos. Nesse cenário, o controle biológico apresenta microrganismos não patogênicos capazes de inibir o desenvolvimento de patógenos como uma alternativa inteligente de manejo de doenças, dentre os quais o B. subtilis é um dos gêneros mais estudados. A rizobactéria se ressai por atuar inibindo uma vasta gama de fitopatógenos através de interações de antagonismo ou indução de resistência sistêmica em plantas. Nesse contexto, o presente trabalho teve como objetivo avaliar o B. subtilis como agente de biocontrole de fitopatógenos da cultura da soja. Para o experimento foi adotando um delineamento de blocos ao acaso, com quatro repetições. Seis tratamentos foram estudados: T1, testemunha (sem aplicação), T2, B. subtilis em V3; T3, padrão fungicida; T4, B. subtilis em V3 + padrão fungicida; T5, B. subtilis em todas as aplicações e T6, B. subtilis + padrão fungicida em todas as aplicações, nos quais foram realizadas cinco aplicações: no estádio vegetativo da soja (V3), no estádio reprodutivo (R1) e três aplicações finais com intervalo de 15 dias. Avaliou-se no experimento: severidade de doença, desfolha e produtividade. Os resultados mostraram que o B. subtilis se apresenta como uma alternativa promissora no controle da ferrugem quando utilizado como parte de um programa de manejo integrado de doenças, contribuindo com a redução do uso de fitossanitários, sem que haja perdas na produtividade, uma vez que os tratamentos T4 e T6 registraram as menores médias de severidade e desfolha, juntamente com uma produtividade similar ao tratamento T3.

An Overview of the Epidemiology of Phakopsora pachyrhizi in the State of Mato Grosso, Brazil

This review seeks to expand the knowledge about the epidemiology of Asian sybean rust in the state of Mato Grosso and contribute to ensuring the economic sustainability of soybean crop. It is discussed the Phakopsora pachyrhizi potential of dispersal from Asia to South America and finally to Mato Grosso state. The origin of the Asian soybean rust inoculum within Mato Grosso is addressed by the survival in volunteer and soybean weed plants (Pitelli, 2015) in other crops such as cotton. Data on the adverse environmental effect on the soybean plants survival are shown mainly the water deficit from June to August. Reports on the effect air temperature and mainly solar radiation on the mortality of airborne spores during their anemophilous spread on sunny days are also discussed. This increase of knowledge aims to make the soybean-free period more efficient by the knowledge on the soybean plants survival and on the fungus viability in the month of August. Due to the proximity of soybean farms, during the soybean-free period, in other states (Tocantins, Goiás, Rondônia, etc.) and in other neighbor countries we discuss the likelihood that inoculum in the state may also originate in out-of-state crops during the Mato Grosso soybean-free period.

Directional Selection of Phakopsora pachyrhizi Towards Site-Specific Fungicides in Mato Grosso State

This review focus on the sensitivity reduction of Phakopsora pachyrhizi to site specific fungicides in the Brazilian state of Mato Grosso.The soybean grown area in this state in the 2018/19 growing season was 9,756,668 hectares. The main crop disease is Asian soybean rust that depending on disease severity may cause 80% yield reduction. The rust chemical control started in the 2002/003 season with site-specific fungicides applied solo and with 3.6 sprayings/ha/season. For these reasons, the fungus had sensitivity reduction to the fungicides DMIs, QoIs and SDHIs resulting in a short effective life. Anti-resistance strategies were not adopted to prevent or delay the development of soybean rust resistant population to site-specific fungicides. Reduced sensitivity to the target site has been observed for all site-specific fungicides involving cross and multiple resistance resulting in ineffective control. So far, eight mutations in Phakopsora pachyrhizi have been identified conferring reduced sensitivity to DMIs, QoIs and SDHIs but so far specific mutations are not considered in chemical control. The directional selection has occurred and has been aggravated season-after-season by the continuous use of site-specific fungicides in a large area, for 18 season and with more than three sprayings/area/season. The presence of soybean weed in one million hectares of cotton crop infected by rust aggravates the directional selection. Anti-resistance strategies should include sowing at the beginning of the recommended season, avoid the December season and replacing it by February, use of scientific criteria to time the first application and the use of multisite fungicides in all applications and in the entire area cultivated with soybean.