Occurrence of different species of fusarium from wheat in relation to disease levels predicted by a weather-based model in Argentina pampas region.

Fusarium head blight (FHB) is an important disease throughout many of the world wheat-growing areas that have humid to semi-humid climate. The infection happens mainly during the anthesis of the wheat, when there have been favorable conditions of moisture and temperature. The direct relation of the infection to environmental factors makes possible the formulation of mathematical models that predict the disease. The causal agent of the FHB of the spike of wheat is attributed principally to Fusarium graminearum. High economic losses due yield decrease have been recorded in Argentina. In the present work, 67 isolates of Fusarium spp. were obtained from samples of wheat grains from Pampas region from 15 locations distributed in Buenos Aires, Entre Ríos, Santa Fe and Córboba provinces during 2006 and 2007 wheat-growing seasons. The identification of species from monosporic isolates was carried out by morphological characterization and use of species-specific PCR-based assays. Both identification criteria were necessary and complementary for the species determination, since in some cases the molecular identification was not specific. Scanty presence of F. graminearum was observed in 2006 wheat-growing season coinciding with the lack of favorable meteorological conditions for producing FHB infection events. High presence of F. graminearum isolates was observed in 2007 wheat-growing season, in accordance with moderate incidence of the disease according to spatial distribution of FHB incidence values. The aim of this report was to identify the causal agent of the FHB disease by different taxonomic criteria and to relate its occurrence with disease incidence values predicted by a weather-based model in Argentina.

Pyrene degradation by yeasts and filamentous fungi.

The saprotrophic soil fungi Fusarium solani (Mart.) Sacc., Cylindrocarpon didymum (Hartig) Wollenw, Penicillium variabile Sopp. and the yeasts Rhodotorula glutinis (Fresenius) Harrison and Rhodotorula minuta (Saito) Harrison were cultured in mineral medium with pyrene. The remaining pyrene concentrations were periodically determined during 20 incubation days, using HPLC. To assess the metabolism of pyrene degradation we added 0.1 microCi of [4,5,9,10] 14C-pyrene to each fungi culture and measured the radioactivity in the volatile organic substances, extractable, aqueous phase, biomass and 14CO2 fractions. The assays demonstrated that F. solani and R. glutinis metabolized pyrene as a sole source of carbon. Differences in their activities at the beginning of the cultures disappeared by the end of the experiment, when 32 and 37% of the original pyrene concentration was detected, for the soil fungi and yeasts, respectively. Among the filamentous fungi, F. solani was highly active and oxidized pyrene; moreover, small but significant degradation rates were observed in C. didymum and P. variahile cultures. An increase in the 14CO2 evolution was observed at the 17th day with cosubstrate. R. glutinis and R. minuta cultures showed similar ability to biotransform pyrene, and that 35% of the initial concentration was consumed at the end of the assay. The same results were obtained in the experiments with or without glucose as cosubstrate.

Extracellular ABTS-oxidizing activity of autochthonous fungal strains from Argentina in solid medium.

The screening for extracellular oxidases and peroxidases from autochthonous filamentous fungi isolated from different substrates is an important step towards the detection of extracellular fungal oxidative systems. Thirty-one autochthonous fungal strains from Argentina, belonging to different ecophysiological and taxonomic groups, were plate-screened for their ability to produce extracellular oxidoreductases. Modified Kirk solid medium containing the chromogen 2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) was used to determine the presence of this extracellular activity. The fungi tested were grouped according to the colour intensity of the modified Kirk medium in: a) species without extracellular ABTS-oxidizing activity; b) species with low extracellular ABTS-oxidizing activity; c) species with moderate extracellular ABTS-oxidizing activity; d) species with high extracellular ABTS-oxidizing activity. The assay revealed extracellular ABTS-oxidizing activity in 90% of the strains tested. All species of Basidiomycetes used exhibited ABTS-oxidizing activity, except Laeticorticium roseum. Aspergillus terreus and Epicoccum purpurascens (Deuteromycetes) did not show extracellular oxidative activity on ABTS. Agrocybe aegerita, Amauroderma boleticeum, Cladosporium cladosporioides, Coriolopsis rigida, Grammothele subargentea, Graphium putredinis, Hexagona hydnoides, Hexagona papyraceae, Loweporus lividus, Peniophora albobadia, Phellinus everhartii, Phellinus gilvus; Phellinus linteus; Pleurotus laciniatocrenatus, Pycnoporus sanguineus, Rigidoporus ulmarius, Steccherinum rawakense, Talaromyces helicus, Trametes elegans, Trametes pavonia, Trametes villosa and Trichaptum sector are reported here for the first time as species capable of producing ABTS-oxidizing extracellular oxidorreductases.

Biodegradation of aliphatic and aromatic hydrocarbons by natural soil microflora and pure cultures of imperfect and lignolitic fungi.

The biodegradation of aliphatic and aromatic hydrocarbons by natural soil microflora and seven fungi species, including imperfect strains and higher level lignolitic species, is compared in a 90-day laboratory experiment using a natural, not-fertilized soil contaminated with 10% crude oil. The natural microbial soil assemblage isolated from an urban forest area was unable to significantly degrade crude oil, whereas pure fungi cultures effectively reduced the residues by 26-35% in 90 days. Normal alkanes were almost completely degraded in the first 15 days, whereas aromatic compounds (phenanthrene and methylphenanthrenes) exhibited slower kinetics. Aspergillus terreus and Fusarium solani, isolated from oil-polluted areas, produced the more efficient attack of aliphatic and aromatic hydrocarbons, respectively. Overall, imperfect fungi isolated from polluted soils showed a somewhat higher efficiency, but the performance of unadapted, indigenous, lignolitic fungi was comparable, and all three species, Pleurotus ostreatus, Trametes villosus and Coriolopsis rigida, effectively degraded aliphatic and aromatic components. The simultaneous, multivariate analysis of 22 parameters allowed the elucidation of a clear reactivity trend of the oil components during biodegradation: lower molecular weight n-alkanes > phenanthrene > 3-2-methylphenanthrenes > intermediate chain length n-alkanes > longer chain length n-alkanes > isoprenoids approximately 9-1-methylphenanthrenes. Irrespective of the individual degrading capacities, all fungi species tested seem to follow this decomposition sequence.

Micobiota de la rizosfera y rizoplano de suelos contaminados con hidrocarburos / Mycobiota from rhizosphere and rhizoplane in hidrocarbon polluted soils

Se estudió la micobiota saprótrofa de suelo rizosférico y de rizoplano, de plantas que crecen en áreas contaminadas con hidrocarburos y en áreas control. Se aislaron e identificaron 52 especies fúngicas, de las cuales 39 pertenecen a los deuteromycetes, 3 a los ascomycetes, 8 a los zygomycetes (orden mucorales) y 2 son micelios estériles. Mediante el uso de métodos de ordenación, utilizándose el análisis de componentes principales, pudo diferenciarse las muestras obtenidas de áreas contaminadas de las no contaminadas. A pesar que las especies son las mismas en ambas áreas, sus frecuencias relativas permiten una discriminación de los muestreos

Uso de líquenes como indicadores biológicos de contaminación atmosférica; aplicación al Gran La Plata

Se contempla el uso de líquenes como indicadores biológicos de contaminación atmosférica en el área del Gran La Plata. Se han relevado ya las especies arboreas existentes en plazas y espacios abiertos y calles de la ciudad de La Plata y se han elegido cinco hospedantes (forofitos): tipa, paraíso, fresno, sófora y arce. Sobre ellos se han identificado 23 géneros de líquenes y, dentro de ellos 24 especies. Se proyecta aplicar una técnica de muestreo normalizada (perímetro y edad de los individuos hospedantes, altura desde el suelo, orientación) a tres áreas de características ecológicas naturalmente comparables pero potencialmente expuestas a diferentes grados de contaminación. Se aplicará, en principio, la metodología de Hoffman, para el establecimiento del "índice de pureza atmosférica", sobre la base de vigor, vitalidad y sociabilidad (grado de cobertura) de los líquenes, así como de índice ecológico (número promedio de otras epifitas asociadas a cada liquen sobre los mismos forofitos)

Uso de líquenes como indicadores biológicos de contaminación atmosférica; aplicación al Gran La Plata

Se contempla el uso de líquenes como indicadores biológicos de contaminación atmosférica en el área del Gran La Plata. Se han relevado ya las especies arboreas existentes en plazas y espacios abiertos y calles de la ciudad de La Plata y se han elegido cinco hospedantes (forofitos): tipa, paraíso, fresno, sófora y arce. Sobre ellos se han identificado 23 géneros de líquenes y, dentro de ellos 24 especies. Se proyecta aplicar una técnica de muestreo normalizada (perímetro y edad de los individuos hospedantes, altura desde el suelo, orientación) a tres áreas de características ecológicas naturalmente comparables pero potencialmente expuestas a diferentes grados de contaminación. Se aplicará, en principio, la metodología de Hoffman, para el establecimiento del "índice de pureza atmosférica", sobre la base de vigor, vitalidad y sociabilidad (grado de cobertura) de los líquenes, así como de índice ecológico (número promedio de otras epifitas asociadas a cada liquen sobre los mismos forofitos)