Saprophytic fungi on tomato phylloplane: Effect of fungicides and leaf position on abundance, composition and diversity

Fungal isolations were made from leaves of tomato plants cultivated in greenhouses in an area close to La Plata, Argentina. Three different schemes of fungicide application were evaluated: high frequency preventive sprayings (Commercial Greenhouse I), low frequency preventive applications (Commercial Greenhouse II) and no fungicide spraying (Control Greenhouse). Leaves were sampled immediately after second fruit formation from three levels of the foliage: low, medium and high. Plating dilution was used to isolate fungal species. Total c.f.u. number and species composition and diversity were assessed by the plating dilution technique. Fungal populations were most abundant on leaves from lower parts of the foliage in the Control Greenhouse. Diversity varied according to fungicide application frequency and leaf position in the canopy. Higher values were recorded for lower leaves in the Control Greenhouse compared with upper leaves from Commercial Greenhouse II. Likewise position in the canopy influenced the frequency of some species. The implications for natural biological control are discussed.Centro de Investigaciones de Fitopatologí

Clonostachys chloroleuca: A novel pathogen causing cassava root rot disease in Misiones Province, Argentina

Cassava (Manihot esculenta) is a crucial food source facing a threat from Cassava Root Rot Disease (CRRD), often caused by fungi like Fusarium, Lasiodiplodia, Phytophthora, among others. In this study, roots from cassava plants displaying CRRD symptoms were collected in Argentina. The isolated fungus, identified as Clonostachys chloroleuca through morphological and molecular methods, was confirmed as the cause of CRRD. In vitro severity tests revealed a high severity value of 22%. The fungus exhibited vigorous growth on root surfaces, causing deep dark coloration and dry pulp consistency. In vivo assays on cassava plants supported the manifestation of typical CRRD symptoms. This study marks the first report of C. chloroleuca causing CRRD, emphasizing its potential threat to cassava production. Further research is essential to understand its pathogenic mechanisms and validate findings in real-world conditions.Fil: Madrassi, Lucas Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; Argentina. Universidad Nacional de Misiones. Facultad de Cs.exactas Químicas y Naturales. Departamento de Bioquímica Clinica; ArgentinaFil: Gonzalez, R. D.. Universidad Nacional de Misiones. Facultad de Cs.exactas Químicas y Naturales. Departamento de Bioquímica Clinica; ArgentinaFil: Mónaco, C. I.. Universidad Nacional de Misiones. Facultad de Cs.exactas Químicas y Naturales. Departamento de Bioquímica Clinica; ArgentinaFil: Zapata, Pedro Dario. Universidad Nacional de Misiones. Facultad de Cs.exactas Químicas y Naturales. Departamento de Bioquímica Clinica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Alvarenga, Adriana Elizabet. Universidad Nacional de Misiones. Facultad de Cs.exactas Químicas y Naturales. Departamento de Bioquímica Clinica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; Argentin

Saprophytic fungi on tomato phylloplane: Effect of fungicides and leaf position on abundance, composition and diversity

Fungal isolations were made from leaves of tomato plants cultivated in greenhouses in an area close to La Plata, Argentina. Three different schemes of fungicide application were evaluated: high frequency preventive sprayings (Commercial Greenhouse I), low frequency preventive applications (Commercial Greenhouse II) and no fungicide spraying (Control Greenhouse). Leaves were sampled immediately after second fruit formation from three levels of the foliage: low, medium and high. Plating dilution was used to isolate fungal species. Total c.f.u. number and species composition and diversity were assessed by the plating dilution technique. Fungal populations were most abundant on leaves from lower parts of the foliage in the Control Greenhouse. Diversity varied according to fungicide application frequency and leaf position in the canopy. Higher values were recorded for lower leaves in the Control Greenhouse compared with upper leaves from Commercial Greenhouse II. Likewise position in the canopy influenced the frequency of some species. The implications for natural biological control are discussed.Centro de Investigaciones de Fitopatologí

Aislamientos nativos de Trichoderma harzianum inducen resistencia a Zymoseptoria tritici en plantas de trigo

Trichoderma harzianum inducting resistance to Zymoseptoria tritici. Septoria tritici blotch is endemic in the wheat growing cultivated areas of Argentina, which impacts in the crop yield. One management strategy is to use biocontrol agents. The objective of this work was to determine the effectiveness of Trichoderma spp. isolated from soils of different growing regions, as antagonist and characterize the T. harzianum effect throughout the proteolytic activity of the serine protease in the wheat plant. To determine the antagonistic capacities of Trichoderma spp. against Zimoseptoria tritici, wheat plants were grown from seeds coated with each of the ninety isolated Trichoderma. Antagonism was assessed 21 days after inoculation by the capacity of each Trichoderma spp. isolate to restrict the progress of the disease. To measure the increasing proteolytic activity, ten isolated T. harzianum characterized by their inhibitory effect over the pathogen, were chosen. Four isolates of the antagonist (strain 2 and 8, from Los Hornos and 129 and 141 from Manfredi localities) simultaneously decreased the pycnidial coverage percentage with a noted increasing of the serine-protease activity in the susceptible wheat cultivar. This behavior is associated to a biochemical mechanism of defense with an early systemic effect.La Septoriosis del trigo es endémica en las regiones productoras de Argentina, impactando en su rendimiento. Una alternativa de manejo, es el uso de agentes de biocontrol. Se propuso: determinar la efectividad de los aislamientos de Trichoderma obtenidos a partir de suelos de diferentes localidades de la región triguera argentina, sobre el control de la enfermedad y caracterizar la actividad de la serín proteasa (con capacidad antifúngica) del fluido intercelular de trigo generada por los mejores aislamientos. Para determinar la capacidad biocontroladora de los 90 aislamientos de Trichoderma, se sembraron semillas recubiertas con cada uno de los antagonistas y posteriormente las plántulas se inocularon con Zymoseptoria tritici. Se evaluó la capacidad de cada aislamiento del biocontrolador para restringir el progreso de la septoriosis 21 días después de la inoculación. A las plantas tratadas con las 10 mejores cepas de T. harzianum, se les midió el incremento de la actividad proteolítica. Cuatro de los aislamientos (2 y 8, de Los Hornos y 129 y 141 de Manfredi) disminuyeron el porcentaje de cobertura picnidial y se destacaron por el aumento de la actividad proteolítica en un cultivar susceptible. Éste comportamiento se asocia a un mecanismo bioquímico de defensa con un efecto sistémico temprano.Fil: Stocco, Marina Celeste. Universidad Nacional de la Plata. Facultad de Ciencias Agrarias y Forestales. Departamento de Ciencias Biológicas. Centro En Investigación de Fitopatología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mansilla, Andrea Yamila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Biológicas; ArgentinaFil: Mónaco, Cecilia I.. Universidad Nacional de la Plata. Facultad de Ciencias Agrarias y Forestales. Departamento de Ciencias Biológicas. Centro En Investigación de Fitopatología; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Segarra, Carmen Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Biológicas; ArgentinaFil: Lampugnani, Gladys. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Abramoff, Cecilia. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Marchetti, Maria Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Biológicas; ArgentinaFil: Kripelz, Natalia. Universidad Nacional de la Plata. Facultad de Ciencias Agrarias y Forestales. Departamento de Ciencias Biológicas. Centro En Investigación de Fitopatología; ArgentinaFil: Cordo, Cristina C.. Universidad Nacional de la Plata. Facultad de Ciencias Agrarias y Forestales. Departamento de Ciencias Biológicas. Centro En Investigación de Fitopatología; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Consolo, Verónica Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones En Biodiversidad y Biotecnología; Argentin

T-Cell Immune Responses Against Env from CRF12_BF and Subtype B HIV-1 Show High Clade-Specificity that Can Be Overridden by Multiclade Immunizations

BACKGROUND: The extreme genetic diversity of the human immunodeficiency virus type 1 (HIV-1) poses a daunting challenge to the generation of an effective AIDS vaccine. In Argentina, the epidemic is characterized by the high prevalence of infections caused by subtype B and BF variants. The aim of this study was to characterize in mice the immunogenic and antigenic properties of the Env protein from CRF12_BF in comparison with clade B, employing prime-boost schemes with the combination of recombinant DNA and vaccinia virus (VV) vectors. METHODOLOGY/PRINCIPAL FINDINGS: As determined by ELISPOT from splenocytes of animals immunized with either EnvBF or EnvB antigens, the majority of the cellular responses to Env were found to be clade-specific. A detailed peptide mapping of the responses reveal that when there is cross-reactivity, there are no amino acid changes in the peptide sequence or were minimal and located at the peptide ends. In those cases, analysis of T cell polifunctionality and affinity indicated no differences with respect to the cellular responses found against the original homologous sequence. Significantly, application of a mixed immunization combining both clades (B and BF) induced a broader cellular response, in which the majority of the peptides targeted after the single clade vaccinations generated a positive response. In this group we could also find significant cellular and humoral responses against the whole gp120 protein from subtype B. CONCLUSIONS/SIGNIFICANCE: This work has characterized for the first time the immunogenic peptides of certain EnvBF regions, involved in T cell responses. It provides evidence that to improve immune responses to HIV there is a need to combine Env antigens from different clades, highlighting the convenience of the inclusion of BF antigens in future vaccines for geographic regions where these HIV variants circulate

Efecto de la adición de enmiendas orgánicas al suelo sobre la capacidad patogénica de Rhizoctonia Solani: II. Microflora asociada y antagonismo in vitro de los aislados más frecuentes

Se estudia en este trabajo el efecto del agregado de enmiendas al suelo sobre su micoflora y el posible papel de la misma sobre la supresión de la enfermedad provocada por Rhizoctonia solani sobre poroto chaucha. Fueron aplicadas tres diferentes enmiendas (alfalfa enfardada, harina de pescado y compost de champiñón), a dos diferentes dosis. La alfalfa enfardada determinó el máximo incremento en la abundancia de la micoflora. Si bien no pudieron hallarse correlaciones significativas entre los parámetros microbiológicos y los de reducción de la enfermedad los resultados sugieren que el fenómeno de la supresividad puede responder a la estimulación general de la micoflora más que al antagonismo de alguna cepa en particula

Selección de aislamientos de trichoderma spp. Para el control del cáncer bacteriano (Clavibacter michiganensis subsp. Michiganensis) del tomate (Lycopersicum esculentum mill.)

En la presente investigación se evaluaron aislamientos de Trichoderma spp.,obtenidos de plantaciones de tomate de la zona hortícola de La Plata (BuenosAires, Argentina), para controlar el desarrollo in vitro de Clavibacter michiganensissubsp. michiganensis agente causal del cáncer bacteriano del tomate.Utilizando un medio selectivo para Trichoderma spp. se obtuvieron nueve aislamientosde Trichoderma spp. a partir de muestras de suelo usando la técnica dedilución seriada. A través de una prueba in vitro se evaluó su capacidad parasuprimir e inhibir el crecimiento del patógeno, encontrándose que todos ellossuprimían el crecimiento de la bacteria en medio de cultivo entre 14 y 16%, ysólo uno de ellos (aislamiento A4) inhibió aproximadamente en un 15,76% eldesarrollo de la bacteria. Los aislamientos de T. harzianum obtenidos a partir desuelo de plantaciones de tomate de la Plata tienen potencial para actuar frente ainfecciones causadas por C. m. subsp. michiganensis en el cultivo de tomate anivel de invernáculo

Impact of different cropping conditions and tillage practices on the soil fungal abundance of a Phaeozem luvico

Fungal diversity seems to be a good indicator of ecosystem disturbance and functioning. The purpose of this work was to quantify the fungal population as a sensitive indicator of the changes caused by stubble placement in two tillage systems: reduced tillage (RT) and conventional tillage (CT) with and without cropping. To this end, we determined the effect of soil disturbances such as N fertilization, tillage practice, and cropped area on the soil fungal communities of a Phaeozem luvico of the El Salado river basin (Argentina). Soil samples (at 0-10 cm depth) were collected from a field cultivated with wheat at post-harvest, before sowing and at tillering. The relative abundance of individuals of the fungal population was studied on Nash Snyder and Oxgall agar media after different treatments and assessed as colony forming units (CFU/gof soil). The diversity of the fungal population was studied by Shannon´s index (H). The tillage system showed a marked effect only at post-harvest and the number of propagules was highest under RT for both culture media. The largest values of H were found only at post-harvest when Oxgall agar was used. A significant decrease in the values of H was observed when CT and high fertilization was applied in the wheat cropped area. The relative abundance of individuals of the fungal population was different in soils under the different tillage practices

Respuesta de Stylosanthes guianensis Ciat 184 a la fertilización con una baja dosis de fósforo

El objetivo fue evaluar la respuesta sobre el rendimiento de MS de Stylosanthes guianensis a una baja dosis de fósforo. El diseño experimental fue bloques completos al azar, con cuatro repeticiones. Los tratamientos fueron PO y P 11kg ha, usando superfosfato triple, aplicado al voleo e incorporado en el momento de la siembra. El suelo pertenece a la Serie Ensenada Grande, clasificado como psamaquent típico. Las semillas se escarificaron, se inocularon y se sembró a una densidad de 3 kg ha. Se evaluó vigor de plantas, porcentaje de cobertura, rendimiento mensual y porcentaje de materia seca (MS). Se determinó rendimiento acumulado, contenido de P, K y proteína cruda. Los datos se analizaron con varianza y las diferencias entre medias con Tukey (p< 0,05). Los valores de cobertura fueron superiores en las parcelas fertilizadas (74% vs. 45%). El porcentaje de MS fue menor en las plantas fertilizadas (21,8% vs. 24,6%). El fósforo incrementó en un 100% la producción acumulada, siendo las diferencias estadísticamente significativas (p< 0,05). Los contenidos de P fueron diferentes entre los tratamientos. En un suelo arenoso con muy baja disponibilidad de P, una dosis baja de P permitió incrementar el rendimiento de MS y el contenido de P en planta en esta especi

Trichoderma spp. as elicitors of wheat plant defense responses against Septoria tritici

Leaf blotch of wheat is a widespread and highly active disease that affects wheat production. In addition to the use of chemicals and proper cultivation methods, microbial antagonists are used to control plant pathogens. Trichoderma spp. stimulate a systemic induced response in plants. Therefore, the efficacy of Trichoderma spp. against wheat leaf blotch was evaluated under greenhouse conditions. The susceptible plants were sprayed with Septoria tritici conidiospores. In order to select an efficient method of pretreatment with Trichoderma spp., leaf spraying and seed coating with 14 isolates were tested in 2003 and 2004. The extent of leaf necrosis area and pycnidial coverage was estimated. Antagonism was assessed by the capacity of each Trichoderma spp. isolate to restrict the progress of leaf blotch, 21 days after inoculation. Of the two methods, seed coating was more efficacious against leaf blotch than leaf spraying. Amongst the 14 isolates tested, the isolate prepared from T. harzianum (Th5) produced the highest level of protection. None of the treatments caused changes in plant stem diameter or dry weight. Trichoderma spp. did not get into leaves while S. tritici was present, even in asymptomatic leaf extracts. In addition, the leaf apoplast antifungal proteolytic activity was measured in plants 7, 15, and 22 days after sowing. This antifungal action decreased in plants only inoculated with S. tritici, but increased in those grown from seeds coated with the T. harzianum (Th5) isolate. This increase conferred resistance to the susceptible wheat cultivar. The endogenous germin-like protease inhibitor coordinated the proteolytic action. These results suggest that T. harzianum stimulates a biochemical systemic induced response against leaf blotch