Maria Isabel Balbi-Peña

Differential occurrence of the oxidative burst and the activity of defence-related enzymes in compatible and incompatible tomato-Oidium neolycopersici interactions

The generation and accumulation of hydrogen peroxide (H2O2) and superoxide anion (O2.-), as well as guaiacol peroxidase, catalase, polyphenol oxidase, β-1,3-glucanase and chitinase activity, were studied in leaves of resistant and susceptible tomato genotypes inoculated with Oidium neolycopersici. Plants of the resistant genotype CNPH 1287 (Solanum habrochaites sin. Lycopersicon hirsutum) and susceptible genotype Santa Cruz Kada (S. lycopersicum sin. Lycopersicon esculentum), with the seven-nine and five-seven leaves completely developed, respectively, were inoculated in the second, third and fourth true leaves. Leaves were collected at the time of inoculation and at 4, 8, 12, 24, 48, 72, 96 and 120 h post inoculation (hpi). The production and accumulation of H2O2 and O2.- were evaluated in situ using diaminobenzidine and nitroblue tetrazolium, respectively. Starting at 24–48 hpi, high accumulation of H2O2 and O2.- was detected, and epidermal cells demonstrated a hypersensitive response, especially in the inoculated leaves of the resistant plant (S. habrochaites). An increase in guaiacol peroxidase, catalase, polyphenol oxidase, β-1,3-glucanase and chitinase activity was mainly detected by 24 hpi in the resistant plant. An association between the production of reactive oxygen species and the activity of enzymes related to reactive oxygen species metabolism (guaiacol peroxidase, catalase), hydrolytic enzymes (β-1,3-glucanase and chitinase) and phenol metabolism enzymes (polyphenol oxidase), as well as hypersensitive response, was evident during the defence responses of the resistant plants when inoculated with O. neolycopersici.

The Effect of Phenazine-1-Carboxylic Acid on Mycelial Growth of Botrytis cinerea Produced by Pseudomonas aeruginosa LV Strain

One of the most important postharvest plant pathogens that affect strawberries, grapes and tomatoes is Botrytis cinerea, known as gray mold. The fungus remains in latent form until spore germination conditions are good, making infection control difficult, causing great losses in the whole production chain. This study aimed to purify and identify phenazine-1-carboxylic acid (PCA) produced by the Pseudomonas aeruginosa LV strain and to determine its antifungal activity against B. cinerea. The compounds produced were extracted with dichloromethane and passed through a chromatographic process. The purity level of PCA was determined by reversed-phase high-performance liquid chromatography semi-preparative. The structure of PCA was confirmed by nuclear magnetic resonance and electrospray ionization mass spectrometry. Antifungal activity was determined by the dry paper disk and minimum inhibitory concentration (MIC) methods and identified by scanning electron microscopy and confocal microscopy. The results showed that PCA inhibited mycelial growth, where MIC was 25 μg mL-1. Microscopic analysis revealed a reduction in exopolysaccharide (EPS) formation, showing distorted and damaged hyphae of B. cinerea. The results suggested that PCA has a high potential in the control of B. cinerea and inhibition of EPS (important virulence factor). This natural compound is a potential alternative to postharvest control of gray mold disease.

Biocontrol of Sclerotinia sclerotiorum and white mold of soybean using saprobic fungi from semi-arid areas of Northeastern Brazil

The incidence and the levels of yield loss caused by the white mold of soybean (caused by the fungus Sclerotinia sclerotiorum) have increased in areas of higher altitude at Cerrado and Southern Brazil, causing yield losses of up to 60%. The aim of this study was to select saprobic fungi with the potential to control the white mold of soybean. First, in vitroantagonism screening was carried out to test eight saprobic fungi against S. sclerotiorum. Assessment of S. sclerotiorum mycelial growth was done at four and seven days after its placement on the culture medium. The isolate showing greatest antagonistic effect in all tests/assessments was Myrothecium sp. An in vivo experiment was conducted in a greenhouse and growth chamber, where plants previously treated with eight saprobic fungi were artificially inoculated with S. sclerotiorum. The fungal culture medium (potato-dextrose) and the commercial resistance inducer acibenzolar-S-methyl were used as controls. In the in vivotests, severity of the white mold was assessed at 8, 14 and 21 days after inoculation. The highest reduction percentage in the lesion length was observed for the treatment with Myrothecium sp. (70%), which has the greater potential to be used as biocontrol agent of soybean under the conditions of this experiment.

Seleção de cultivares de soja para resistência à podridão negra da raiz (Macrophomina phaseolina)

A seleção a campo de materiais resistentes à podridão negra da raiz, além de ter alto custo, apresenta alta variabilidade, uma vez que muitos fatores externos podem afetar o comportamento das plantas e, inclusive, do fungo, de local para local e de ano para ano. Seleção de variedades com resistência à podridão causada por Macrophomina phaseolina em casa de vegetação apresenta maior uniformidade e estabilidade dos resultados, uma vez que as condições são controladas. No entanto, é recomendado que os resultados obtidos em ambiente protegido, para serem adotados como protocolo de screening, apresentem boa correlação com resultados obtidos em campo. Assim, este trabalho teve por objetivo comparar a eficiência de métodos de screening em casa de vegetação e verificar suas correlações com o comportamento de variedades de soja em ensaio de campo. Os métodos de screening avaliados foram disco de micélio sobre haste cortada; punção da haste com palito colonizado; solo infestado por inóculo produzido em arroz (1g, 5g e 10g por kg de solo); e rega com suspensão de microescleródios (3 x 10 e 6 x 10 UFC/mL) sobre raízes de plântulas. O ensaio de campo foi montado em área com histórico de ocorrência da doença, e o solo foi infestado com sementes de sorgo colonizadas por M. phaseolina, no sulco de semeadura. Plantas inoculadas na haste, em casa de vegetação, foram submetidas a duas condições de umidade: câmara úmida por três dias Ishikawa, M.S.; Ribeiro, N.R.; Oliveira, E.C.; Almeida, A.A.; Balbi-Peña, M.I. Seleção de cultivares de soja para resistência à podridão negra da raiz (Macrophomina phaseolina). Summa Phytopathologica, v.43, n.4, p.38-44, 2018.

Control del moho azul en poscosecha de manzana con productos naturales

espanolEl uso de los extractos vegetales con actividad antimicrobiana para controlar enfermedades en pre o poscosecha es una alternativa promisoria frente al uso de fungicidas sinteticos. El objetivo de este estudio fue evaluar el efecto de extractos vegetales y aceites esenciales en manzanas infectadas naturalmente con Penicillium spp., agente causal del moho azul. Se sumergieron manzanas en extractos de citricos y de neem (Azadirachta indica) en concentraciones de 0,5 y 1,0% (v/v) y se almacenaron a 25 °C y 90% de humedad relativa. Despues de 21 dias se midio incidencia y severidad de la enfermedad. Tambien se evaluo el efecto de los aceites esenciales de Thymus vulgaris, Origanum vulgaris, Mentha piperita y Melaleuca alternifolia por fumigacion. La fruta se almaceno a 25±2 °C y 90±5% de humedad relativa durante 21 dias. Frutos tratados con agua destilada esteril constituyeron el tratamiento control. Los frutos sin tratar presentaron los valores mas altos de incidencia (100%) y severidad (99,98%) de moho azul, asi como el menor porcentaje de control (4,56%). Todos los tratamientos mostraron efecto antifungico de Penicillium spp, sin embargo, los extractos citricos y de A. indica en la concentracion de 1,0% proporcionaron los mayores niveles de control de la enfermedad (99,57% y 98,33%, respectivamente). Los frutos tratados con aceites esenciales mostraron menor incidencia, menor severidad y mayor control de la enfermedad. Se ha demostrado que el extracto y aceites esenciales estudiados tienen actividad antifungica y potencial para uso en poscosecha como una alternativa al control quimico. EnglishPlant extracts for the control of plant disease are emerging as promising alternatives to the use of synthetic fungicides. The objective of this work was to study the effect of plant extracts and essential oils on naturally infected apple fruits with Penicillium spp. causal agent of blue mold. Apple fruits were immersed in citric and Azadirachta indica extracts at concentrations of 0.5 and 1.0% (v/v), stored at room temperature (25 °C and 90% RH) and analyzed at 21 days after the application of the treatments. Evaluated also the effect of fumigation of apple fruits with essential oils of Thymus vulgaris, Origanum vulgaris, Mentha piperita and Melaleuca alternifolia. Treated fruits were stored at 25±2 °C and 90±5% relative humidity for 20 days. Treated fruit with distilled water constituted the group controls. The higher values of incidence (100%), severity (99.98%) and the lowest percentage of disease control (4.56%) were observed in apple fruits treated with distilled water (group control). All treatments exhibited inhibitory effect on Penicillium spp. in apple fruits, however, A. indica and citric extracts, at concentrations of 1.0%, had a disease control of98.33% and 99.57%, respectively. There were no significant differences between the oils applied; except between these and the control. However, the treatments with essential oils were that exhibited the least incidence, severity and control of the disease. The results showed that essential oils showed good results, above 98.1% of control of blue mold disease in postharvest. It was demonstrated that extracts the different concentration and essential oils have antifungal activities and that they have a potential use as an alternative control in relation to chemical methods.