Microorganismos potencialmente fitopatógenos en aguas de riego proveniente de la cuenca media del rio Bogotá / Potentially phytopathogenic microorganisms irrigation water from the media Bogota river basin

Resumen Objetivo. Identificar microorganismos fitopatógenos presentes en las aguas utilizadas para riego en la cuenca media del rio Bogotá. Métodos. Las muestras fueron tomadas en doce fincas de la cuenca media y analizadas con la técnica de filtración por membrana. Las bacterias se identificaron por bioquímica y los hongos por claves dicotomas. Resultados. El agua de riego analizada contenía bacterias como: E.coli, P. vulgaris, A. urinae, E. cloacae, B.cereus, S. marcescens, B. brevis, y en cuanto a los hongos se encontraron: Aspergillus fumigatus, Aspergillus flavus., Mucor sp., Rhizopus sp., Penicillium sp. y Fusarium sp. La presencia de estos potenciales fitopatógenos en el agua indican un alto riesgo de contaminación y dispersión de éstos en los cultivos.

Abstract Objective. Identify phytopathogenic microorganisms present in the water used for irrigation in the middle basin of the river Bogota. Methods. Samples were taken at 12 farms of the middle basin and analyzed by the membrane filtration technique. The bacteria were identified by biochemical and fungi by dichotomies keys. Results. The irrigation water contained bacteria analyzed as E. coli, P. vulgaris, A. urinae, E. cloacae, B. cereus, S. marcescens, B. brevis, and as for the mushrooms found: A. fumigatus, A. flavus, Mucor sp., Rhizopus sp., Penicillium sp. and Fusarium sp. The presence of these potential pathogens in water indicate a high risk of contamination and dispersion thereof in crops.

Isolation and expression of two polyketide synthase genes from Trichoderma harzianum 88 during mycoparasitism

Abstract Metabolites of mycoparasitic fungal species such as Trichoderma harzianum 88 have important biological roles. In this study, two new ketoacyl synthase (KS) fragments were isolated from cultured Trichoderma harzianum 88 mycelia using degenerate primers and analysed using a phylogenetic tree. The gene fragments were determined to be present as single copies in Trichoderma harzianum 88 through southern blot analysis using digoxigenin-labelled KS gene fragments as probes. The complete sequence analysis in formation of pksT-1 (5669 bp) and pksT-2 (7901 bp) suggests that pksT-1 exhibited features of a non-reducing type I fungal PKS, whereas pksT-2 exhibited features of a highly reducing type I fungal PKS. Reverse transcription polymerase chain reaction indicated that the isolated genes are differentially regulated in Trichoderma harzianum 88 during challenge with three fungal plant pathogens, which suggests that they participate in the response of Trichoderma harzianum 88 to fungal plant pathogens. Furthermore, disruption of the pksT-2 encoding ketosynthase–acyltransferase domains through Agrobacterium -mediated gene transformation indicated that pksT-2 is a key factor for conidial pigmentation in Trichoderma harzianum 88.

Soft computing model on genetic diversity and pathotype differentiation of pathogens: A novel approach

Background Identifying and validating biomarkers' scores of polymorphic bands are important for studies related to the molecular diversity of pathogens. Although these validations provide more relevant results, the experiments are very complex and time-consuming. Besides rapid identification of plant pathogens causing disease, assessing genetic diversity and pathotype formation using automated soft computing methods are advantageous in terms of following genetic variation of pathogens on plants. In the present study, artificial neural network (ANN) as a soft computing method was applied to classify plant pathogen types and fungicide susceptibilities using the presence/absence of certain sequence markers as predictive features. Results A plant pathogen, causing downy mildew disease on cucurbits was considered as a model microorganism. Significant accuracy was achieved with particle swarm optimization (PSO) trained ANNs. Conclusions This pioneer study for estimation of pathogen properties using molecular markers demonstrates that neural networks achieve good performance for the proposed application.

Antimicrobial Activity of Bacteria Associated with Seaweeds against Plant Pathogens on Par with Bacteria Found in Seawater and Sediments.

Aim: We report antimicrobial activities of bacteria associated with 10 native and one invasive species of seaweeds on par with bacteria found in the seawater and sediment. Bacteria exhibiting antimicrobial activity were phylogenetically analysed using 16S rRNA gene. Place and Duration of Study: Samples of seaweeds, seawater and sediments collected at 6 localities of south east coast of India between December 2009 and January 2010 during monsoon season. Methodology: Culturable bacteria in seaweeds (epibiotics and endobiotics), seawater and sediments were isolated through serial dilutions using 1.5% ZoBell marine agar (HiMedia, India). Bacterial isolates producing antibiotics were identified by screening against commercial antibiotics and they were subjected to morphological, Gram’s staining and biochemical studies. Chemical property and stability of antimicrobial substances obtained from the promising bacteria active against plant pathogens were studied. Phylogenetic analysis of antibiotics-producing marine bacteria was made using 16S rRNA gene sequencing technique. Results: A number of673 isolates obtained through the isolation process were found to be the member of 27 bacterial genera, with species of Bacillus recording a maximum of 40.2%. Generally species of bacterial isolates in the association (seaweeds: epibiotics, 39.54% and endobiotics, 40.74%, seawater 8.61% and sediments 11.11%) produced antibiotics and active against plant pathogens (Xanthomonas axonopodis pv. citri, X. oryzaepv. oryzae and Ustilaginoidea virens) were associated with seaweeds (epibiotics 33.46% and endobiotics 43.11%) and sediments (23.43%). Extracellular components of active bacteria are proteins and retaining bioactivity at pH 7.0, up to 40°C and antifungal property up to 60°C. Extracts obtained from the active bacteria are nonpolar lipophilic substances exhibited only antifungal activity. Conclusion: Bacterial population were considerably higher in seaweeds as compared to seawater and sediments, and at the same time higher bacterial population was recorded in Gulf samples than the open coast samples. Most of the bacterial isolates associated with seaweeds were found to produce antibiotics.

Role of Different Additives on Survival of Serratia plymuthica HRO-C48 on Oilseed Rape Seeds and Control of Phoma lingam

For optimum inhibition of plant pathogens, biocontrol agents must be maintained at higher density and survive for a long time in the plant system. Biopriming of seeds with bacteria in the presence of different additives provide a promising technique that might improve the efficacy of biocontrol agents and their application. The aim of this work was to test different additives and stickers on the activity of Serratia plymuthica in oilseed rape in controlling Phoma lingam. Seeds were soaked in bacterial suspensions (log10 11 CFU ml-1) containing one of the following Stickers and additives in a ratio of 1:1:1 (w:v:v): Sodium alginate, Dextran T 40, Polyvinyl alcohol, Methylcellulose, Gum Arabic, Raffinose, Tween 20, and Paraffin oil. Seeds were stored either at room temperature or at 4°C. Number of bacteria inside the seeds was monitored over a period of 12 months. The effect of additives and stickers on bacterial efficacy in controlling Phoma lingam was evaluated in pot experiments. Number of bacterial cells inside the seeds was significantly higher in the seeds coated with GA+MgSO4, RF+MC and PA (log10 7.5 ± 0.2, log10 7.5 ± 0.2 and log10 7.4 ± 0.4, respectively). Interestingly, bacterial concentration in seeds stored at 4°C was higher than that in seeds stored at 20°C. Moreover, after storage for 8 months, Serratia plymuthica was able to control the black leg disease. Our results showed that some additives and stickers prolonged the shelf life of bacteria inside the seeds and improved the efficacy of bacteria in controlling the disease.

In vitro sensitivity of antagonistic Trichoderma atroviride to herbicides

Trichoderma atroviride was tested in vitro for its sensitivity to different herbicides. The dosages tested were recommended dosage (RD), half dosage (½RD), and double dosage (2RD). Germination, colony-forming units (CFU), radial growth, and spore production were evaluated. Carfentrazone-ethyl and sulfentrazone inhibited the germination at RD and 2RD. A reduction in the CFU was observed for glufosinate-ammonium, atrazine, carfentrazone-ethyl, diuron + paraquat dichloride, imazapyr, oxyfluorfen, and sulfentrazone at each of the tested dosages. Radial growth was influenced by ametryn, atrazine, carfentrazone-ethyl, oxyfluorfen, and sulfentrazone herbicides, with an 80% reduction of the colonial area. Spore production was affected by carfentrazone-ethyl, oxyfluorfen, and sulfentrazone with colonial area reductions of over 70%. It was concluded that 2,4 D, clomazone, and imazapyr herbicides showed the least toxicity to T. atroviride and should be used in the crops where the fungus has been applied for phytopathogen control.

Efecto del control biológico por antagonistas sobre fitopatógenos en vegetales de consumo humano / Biological control effect by antagonist on plant pathogens in vegetables for human consumption

Tomando en consideración el efecto adverso que provocan los pesticidas al medio ambiente y la salud y la posibilidad de al menos minimizar su uso, se investigó el efecto del control biológico de tres antagonistas microbianos (Trichoderma viride, Pseudomonas aeruginosa y Bacillus subtilis), sobre fitopatógenos causantes de enfermedades en vegetales como: tomate, cebolla y pimentón. Los ensayos se realizaron en semillas de estos tres rubros infectadas experimentalmente con tres fitopatógenos (Phytophthora spp, Fusarium monilliforme y Rhyzoctonia solani). Inicialmente, el efecto de los antagonistas sobre los fitopatógenos se determinó en medios de cultivo Sabouraud sólido (agar) y líquido (caldo). Posteriormente, 35 semillas de cada una de las especies vegetales seleccionadas se sometieron a diferentes tratamientos: I-Grupo control, sin ninguna adición; II-Grupo tratado con los antagonistas y III-Grupo infectado con los fitopatógenos. Todos los grupos se sembraron en tierra abonada, a cielo abierto y a temperatura ambiente y regados dos veces diariamente con agua. Adicionalmente, al grupo III se le agregó diariamente un inóculo de 0,1 mL de antagonista (10(4) UFC/mL). El desarrollo de las plantas se monitoreo por dos semanas determinándose el número de semillas germinadas, la longitud de las plántulas y el follaje. Los resultados se analizaron a través de Statistix 8.0, pruebas Tukey y Kruskal-wallis. Los antagonistas inhibieron la proliferación de los fitopatógenos en medio Sabouraud. Los experimentos con semillas demostraron una mayor estimulación de la germinación y tamaño de las plántulas en el grupo tratado con fitopatógenos y antagonistas respecto al grupo control (p<0,1).

Taking in account the negative actions of pesticides exert on natural environment and health and due to the possibility to minimize/eliminate its use, the effect of microbial antagonist (Trichoderma viride, Pseudomonas aeruginosa and Bacillus subtilis), were evaluated on tomato, onion and pimento seeds experimentally infected with three known phytopatogens (Phytophthora spp, Fusarium monilliforme and Rhyzoctonia solani). Initially, the antagonist effect on the phytopatogens were studied on Sabouraud solid (agar) and liquid (broth) media. Further 35 seeds of each vegetable were treated according to the following experimented protocol group I (control): no addition and water, group II (treated): antagonist and water, group III (infected): antagonist, water and phytopathogens. All groups were grown on soil, under sun light, at room temperature and water was added twice a day. Group III was daily infected with 0,1 mL of the antagonist suspensions (10(4) UFC/mL). The plant development was followed for 2 weeks, determining number of germinated seeds (germination index), plantule length and foliage. The results obtained was analyzed with Statistix 8.0, Tukey and Kruskal-Wallis. The antagonist inhibited the proliferation of the phytopathogens in Sabouraud media. The seed treated and infected showed a higher index of germination and plantule respect to the control and treated groups (p<0,1).

Volatiles produced by interacting microorganisms potentially useful for the control of plant pathogens / Voláteis produzidos pela interação entre microorganismos potencialmente úteis no controle de fitopatógenos

The results of studies about interactions between microorganisms involving at least one plant pathogen are of interest to the areas of ethiology and control in Plant Pathology. Various aspects of these interactions have been studied over the years but the toxicity of volatile organic compounds (VOCs) has been emphasized only recently, developing techniques and procedures, and producing additional knowledge to those already obtained with water-soluble substances. This new facet of these interactions based on VOCs is discussed in this review involving mainly fungi, bacteria and nematodes pathogenic to plants. Also discussed is the role of VOCs produced by microorganisms, especially fungi and bacteria, in soil fungistasis and the effect of VOCs on fungal agents used in the control of plant parasitic nematodes. The evidence of VOCs broadens the research studies about these interactions. However, the scarcity of the research results in this area show up gaps which need to be filled and some research proposals are discussed. The present and future accumulated VOC knowledge will perhaps be beneficial to farmers, especially aspects related to increasing soil suppressiveness to plant disease and to the finding of analog molecules of VOCs highly effective against plant pathogens.

Os resultados dos estudos sobre interações entre microorganismos quando envolve, no mínimo, um patógeno de plantas são de interesse às áreas de etiologia e controle de fitodoenças. Vários aspectos dessas interações têm sido, por muitos anos, estudados, porém, a toxicidade de compostos orgânicos voláteis (COV) tem sido enfatizada apenas recentemente, desenvolvendo-se técnicas e rotinas, além de produzir conhecimentos adicionais àqueles já obtidos por meio de pesquisas com substâncias solúveis em água. Essa nova faceta dessas interações, envolvendo COVs, é discutida nesta revisão, enfatizando, principalmente, o antagonismo a fungos, bactérias e nematóides patogênicos de plantas. Também é discutido o papel dos COVs produzidos por microorganismos especialmente, fungos e bactérias envolvidos na fungistase do solo, bem como o efeito dos COVs nos agentes fúngicos usados no controle de fitonematóides. A evidência comprovada dos COVs nessas interações amplia esse campo de pesquisa. Entretanto, a escassez de pesquisas nessa área afloram lacunas no conhecimento científico que precisam ser preenchidas e, desta forma, algumas propostas de pesquisas são discutidas. O conhecimento científico presentemente acumulado nessa área de pesquisa, juntamente com aquele a ser produzido, serão, talvez, úteis aos produtores rurais, especialmente nos aspectos envolvendo a constatação de supressividade de solo a fitodoenças e aos testes com moléculas análogas dos COVs altamente tóxicos a patógenos de plantas.