Studies on Pathogenesis of the Diseases Caused by Macrophomina phaseolina and Phomopsis longicolla on Soybean

Soybean (Glycine max), a legume, is an economically important crop in many parts of the world, including the USA, Brazil, Argentina, China, and India, currently the top five producing countries. Soybean is primarily used as feed, with incising markets for food and biodiesel. Similar to most crops, soybean yield and quality are affected by a diverse group of plant pathogens. In particular, several species of filamentous fungi have been the cause of severe yield losses in most growing regions world-wide. The soil born fungus Macrophomina phaseolina, causal agent of charcoal rot, has been found to be endemic to several soybean production areas. Charcoal rot has been historically associated with severe yield reduction, particularly when coupled with drought stress. However, little is known about how irrigation-regimes change affect the relationship between disease severity and yield. A different soil and seed born fungus Phomopsis longicolla, causes severe seed decay under conducive environmental conditions, warm and wet weather during soybean senescence. Although both fungi co-inhabit soybean roots and stems for extended periods of times, little is known about their interactions. Recently, P. longicolla has been shown to be amenable to genetic manipulation via Agrobacterium tumefaciens. However, no study has yet taken advantage of this amenability to dissect potential mechanisms associated to Phomopsis seed decay. This study was designed to understand how different irrigation regimes may impact severity of charcoal rot and its relationship to soybean yield. Additionally, the interplay between M. phaseolina and P. longicolla in soybean tap roots via the formation of zone lines was investigated. Lastly, taking advantage of available genetic transformation methodology, experiments were implemented to elucidate putative molecular mechanisms of Phomopsis seed decay pathogenesis. Results indicated that drought stress significantly increases charcoal rot severity and decreased yield. However, no consistent relationship was observed between these variables. Observations also showed that P. longicolla forms zone lines in soybean taproots thereby precluding M. phaseolina from colonizing these tissues. In this study, for the first time, forward and reverse genetic approaches and transcriptomics were employed on P. longicolla successfully. Multiple genes linked to decreased pathogenicity were identified in P. longicolla

Effect of infection site and glyphosate application on the foliar symptoms expression of soybean sudden death syndrome

Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is an important root disease that can cause root rot and express foliar symptoms leading to premature defoliation and yield reduction. Earlier reports suggested that the germination of F. virguliforme macroconidia and penetration of their germination tube may differ among the sites along the root system of soybean plants. Glyphosate [N-(phosphonomethyl) glycine] is a post-emergent broad spectrum non-selective herbicide that is largely used in soybean production systems. Previous study shows that infection does not always lead to disease in this host-pathogen interaction as the fungus can reach high level of infection of colonization and remain asymptomatic. Expression of foliar symptoms is critical to the occurrence of SDS. The objectives of this study were (1) to assess effects of different root inoculation sites on foliar symptom expression and the effect of mechanical injury of seedling tap roots on foliar symptoms expression of SDS and (2) to evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experimentsWe evaluated three different sites of infection: root tip, middle root portion and upper root. After inoculation, seedlings were transplanted to cones filled with sterile potting mixture. Rhizosphere temperature was controlled by using a water bath (20°C). Plants were evaluated three weeks after transplanting for incidence and severity of SDS. Root sites were not significant for incidence of SDS. Higher incidence was observed when root tips were wounded, probably because tissue wound increased xylem infections. A field survey was done to compare disease levels for plants grown in greenhouse to plants in the fields. Adjacent symptomatic and asymptomatic plants were collect from three fields naturally infested with F. virguliforme. Our results suggested that F. virguliforme can infect plants and remain asymptomatic at a high incidence level. To evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experiments were conducted using 4 glyphosate-tolerant soybean cultivars, P92Y51, P93Y13, P93Y13, and P93Y13, that were planted in soil inoculated with F. virguliforme and sprayed with 4 different application rates of glyphosate 0, 1.2, 1.6, and 2.4 L ha-1 of Roundup Ultra ®, plants were sprayed 2 weeks after planting. Incidence and severity of foliar symptoms were evaluated as well as plant height. Our results show that specific cultivars and rates of glyphosate can increase incidence and severity of SDS foliar symptoms

Interdisciplinary Team Addresses Cotton Leafroll Dwarf Virus in Alabama

A multi-state and interdisciplinary team was formed to address the Extension and research needs of CLRDV, an emerging cotton disease with high potential impact for U.S. cotton production. In 2017, CLRDV was identified in AL and Auburn University immediately formed an interdisciplinary working group composed of plant breeders, plant pathologists, entomologists, and agronomists. Since then, scientists from ten other states have joined the CLRDV group. Thus, allowing research to be coordinated efficiently and best deploy limited resources to attend the stakeholder’s needs. The CLRDV group produces and shares new and relevant information with the scientific community and cotton producers alike

Effect of infection site and glyphosate application on the foliar symptoms expression of soybean sudden death syndrome

Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is an important root disease that can cause root rot and express foliar symptoms leading to premature defoliation and yield reduction. Earlier reports suggested that the germination of F. virguliforme macroconidia and penetration of their germination tube may differ among the sites along the root system of soybean plants. Glyphosate [N-(phosphonomethyl) glycine] is a post-emergent broad spectrum non-selective herbicide that is largely used in soybean production systems. Previous study shows that infection does not always lead to disease in this host-pathogen interaction as the fungus can reach high level of infection of colonization and remain asymptomatic. Expression of foliar symptoms is critical to the occurrence of SDS. The objectives of this study were (1) to assess effects of different root inoculation sites on foliar symptom expression and the effect of mechanical injury of seedling tap roots on foliar symptoms expression of SDS and (2) to evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experimentsWe evaluated three different sites of infection: root tip, middle root portion and upper root. After inoculation, seedlings were transplanted to cones filled with sterile potting mixture. Rhizosphere temperature was controlled by using a water bath (20°C). Plants were evaluated three weeks after transplanting for incidence and severity of SDS. Root sites were not significant for incidence of SDS. Higher incidence was observed when root tips were wounded, probably because tissue wound increased xylem infections. A field survey was done to compare disease levels for plants grown in greenhouse to plants in the fields. Adjacent symptomatic and asymptomatic plants were collect from three fields naturally infested with F. virguliforme. Our results suggested that F. virguliforme can infect plants and remain asymptomatic at a high incidence level. To evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experiments were conducted using 4 glyphosate-tolerant soybean cultivars, P92Y51, P93Y13, P93Y13, and P93Y13, that were planted in soil inoculated with F. virguliforme and sprayed with 4 different application rates of glyphosate 0, 1.2, 1.6, and 2.4 L ha-1 of Roundup Ultra ®, plants were sprayed 2 weeks after planting. Incidence and severity of foliar symptoms were evaluated as well as plant height. Our results show that specific cultivars and rates of glyphosate can increase incidence and severity of SDS foliar symptoms.</p

Pontas de pulverização e horários de aplicação no controle químico de ferrugem asiática da soja

Spray nozzles were evaluated at two different spraying times (14h and 17h 30m), in Mato Grosso do Sul, Brazil regarding Asian soybean rust control (Phakopsora pachyrhizi Sidow). Four spray nozzles were evaluated: deflector plain tips, double deflector plain tips, extended range flat spray tips and double plain tips. A commercial formulation of epoxiconazole and pyraclostrobin (0,5 L ha-1) was sprayed in the plots. Soybean leaves were collected at the top, middle and lower canopy, for assessment of the number of lesions and uredinias. In addition, leaf area affected by P. pachyrhizi was estimated. Plots sprayed with double deflector plain tips had lower uredinia counts in the lower canopy compared to the other tips tested. Sprays done early in the afternoon with double deflector plain nozzles had lower uredinia counts compared to the other treatments. Smaller defoliation and greater a-thousand grain mass were detected in plots sprayed with fungicide using a double deflector plain tip compared to the deflector plain nozzle. Soybean yield was not affected by nozzles and time of fungicide spray.O trabalho foi desenvolvido em Dourados-MS, com o objetivo de estudar o efeito de pontas de pulverização e horários de aplicação de fungicida no controle químico da ferrugem asiática da soja (Phakopsora pachyrhizi Sidow). Avaliaram-se quatro pontas de pulverização: jato plano defletor, jato plano defletor duplo, já to plano de faixa ampliada, jato plano duplo. As aplicações ocorreram nos horários de 14h e 17h 30min com pulverizador costal à pressão constante. O fungicida utilizado foi uma formulação comercial de epoxiconazol e piraclostrobina (0,5 L ha-1). Foram coletados folíolos nos terços superior, médio e inferior para avaliação do número de lesões, urédias, e área foliar lesionada. Menor número de urédias no terço inferior foi observado em plantas que receberam aplicação de fungicida às 14h via ponta jato plano defletor duplo em relação às demais pontas. A aplicação de fungicida, independente do tipo de ponta, não resultou em alterações nos níveis de controle da ferrugem asiática nos terços superior e médio. Menor desfolha e maior massa de mil grãos foram detectadas quando a aplicação foi realizada com a ponta jato plano defletor duplo em relação à jato plano defletor. A produtividade não foi afetada pelo uso de diferentes pontas e horários de aplicação do fungicida

Resumos concluídos - Engenharia de Materiais

Resumos concluídos - Engenharia de Materiai