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Dark energy is an elusive concept, which has been introduced two decades ago in order to make the acceleration of the universe a comprehensible phenomenon. However, the nature of this energy is far from being understood, both from a fundamental as well as an observational way. In this work, we study cosmological consequences of the existence of particles (which we called "ewkons" in a previous work) which are quasi distinguishable, obey unorthodox statistics, and have an equation of state similar to many existent dark energy candidates (including negative relation between pressure and energy density). We find an effective scalar field description of this ewkon fluid, and obtain cosmological solutions for the dark energy-dominated epoch. This can be considered as a one-parameter class of dark energy models. [ABSTRACT FROM AUTHOR]

Wheat grain discoloration, a worldwide disease that lowers grain quality and decreases grain yield, does not have a single etiology. It has been proposed that it is a consequence of an abiotic mechanism, a response to environmental conditions or enzymatic activity. It has also been suggest that it is a biotic mechanism, a fungal infection principally by Alternaria spp. and Bipolaris sorokiniana. The present work was carried out to analyze the possible etiology of this disease in nine durum wheat genotypes from two localities of southern Buenos Aires province (Argentina) on two sowing dates. Incidence (percentage of grain discoloration) was recorded and mycobiota associated with this pathology was registered following ISTA rules. Peroxidase activity in an extract obtained from grains belonging to genotypes of the locality that showed the highest incidence was measured. The incidence among genotypes, localities and sowing dates varied, although the genotypes with the higher and lower values of incidence were the same for all the variables tested. The fungus Alternaria spp. was isolated the most frequently followed by Fusarium spp., while Bipolaris sorokiniana was found the least frequently. Peroxidase activity showed that all the treatments had similar levels of enzymatic activity, but there was no clear differentiation between controls either between genotypes with the lowest or the highest incidence values. This suggests that peroxidase activity did not have a clear relationship with grain discoloration. In this research, it is presumed that fungal infection is the main cause of this disease. [ABSTRACT FROM AUTHOR]

Many species of Trichoderma produce secondary metabolites such as volatile organic compounds (VOCs) that reduce plant diseases and promote their growth. In this work we evaluated the antagonistic effects of VOCs released by eight strains of two Trichoderma species against Pyrenophora teres Drechsler, the causal agent of barley net blotch. Antagonism was estimated based on the percentage of mycelial growth inhibition according to the confronted cultures method. VOCs extraction and identification were performed by gas chromatography and mass spectrometry, through different methodologies for VOCs emitted by antagonists and pathogens alone or when confronted. VOCs produced by all Trichoderma strains inhibited mycelial growth of the pathogen in a range of 3 to 32%, showing weak and unpigmented mycelia with vacuolization. In addition, P. teres stimulated the release of VOCs by both Trichoderma species. The major groups of VOCs detected were sesquiterpenes, followed by diterpenes, terpenoids and eight-carbon compounds. This is the first report about characterization of volatiles emitted by Trichoderma in the presence of P. teres. [ABSTRACT FROM AUTHOR]

In the present study the aspects of discolouration that could influence both the production and consumption of amaranth were analyzed with the objectives to identify the presence of Alternaria alternata on seeds, to analyze possible changes in the anatomy of seed tissues and to detect the presence of fungal secondary metabolites. Component plating, histopathological and mycological analyses on discoloured seeds allowed i) location of propagules of A. alternata in all seminal components; ii) observation of hypertrophies in perisperm and embryo and iii) determination of several fungal secondary metabolites, mainly high concentrations of tenuazonic acid. To our knowledge, the information presented in this paper, related to physiological, histopathological changes and fungal secondary metabolites on discoloured seeds of (Amaranthus mantegazzianus syn. A. caudatus subsp. mantegazzianus (Pass) Hanelt affected by A. alternata, is the first worldwide record. [ABSTRACT FROM AUTHOR]

Abstract: Fusarium head blight (FHB) is a destructive disease of the world''s wheat-growing areas. In Argentina, the area under reduced tillage has increased due to soil erosion that threatened productivity. The effect of conventional and no tillage systems on FHB combined with other agronomic practices such as nitrogen fertilization, and the influence of the environmental conditions was analysed under natural infection on different cultivars. Wheat trials were conducted in three consecutive years; maize was the previous crop in the first and wheat the previous crop in the subsequent two years of the study. The experimental design was a split plot, with tillage treatments (conventional tillage and no-till) as the main plots. Fertilizer treatments were applied as a range of urea concentrations. Fusarium head blight was observed in all three experimental years. Differences of disease expression among trials were associated with the environmental factors prevailing during the experiments. In the first year, with moderate weather conditions, the only interactions for FHB incidence were between no-till and urea split doses. Seedling emergence, seed health, thousand kernel weight and deoxynivalenol (DON) concentration did not differ suggesting that the fertilizers and genotypes did not affect disease susceptibility. Climatic conditions prevailing in the second year were more conducive to disease development and severe FHB infection was observed. Tillage and fertilization treatments did not affect the variables analysed. Only cultivars showed significant differences and DON values were high. In the third year, unfavourable conditions for disease development resulted in low disease levels and no effect or interaction among variables was observed. The results obtained would suggest that favourable weather conditions are likely to be more important than tillage practice and fertilizer treatments. Since soil conservation practices have been widely adopted in most areas of Argentina, an integrated used of all the available strategies should be considered to decrease FHB damage. [Copyright &y& Elsevier]

Bioassays were conducted under greenhouse conditions to test the efficacy of selected bacterial and fungal antagonists applied to wheat seeds for protection against seedling blight caused by Bipolaris sorokiniana. Initially, 120 wheat rhizobacteria from soils collected at five wheat fields in Argentina were screened by two different paired culture methods. Seven isolates of Trichoderma spp. that previously showed biocontrol activity against necrotrophic pathogens of wheat were also evaluated. The in vitro tests, based on the ability of the antagonists to inhibit mycelial growth of the pathogen, were used to select the most effective isolates for further testing in a plant bioassay conducted on wheat seedlings. Disease severity, disease incidence and dry weight were estimated in the greenhouse 3 weeks after sowing. Out of 120 bacteria, 33 showed moderate to strong inhibition to the mycelial growth of B. sorokiniana on potato dextrose agar in Petri dishes. Thereafter, dual cultures in flasks containing nutrient broth showed that four strains of Bacillus cereus and one isolate of Stenotrophomonas maltophilia exhibited the greatest inhibition (> 77%) to the fungal biomass. All Trichoderma spp. inhibited the mycelial growth of the pathogen by between 51 and 71%. Seed microbiolization failed to supress seedling blight under greenhouse conditions. Nevertheless, Trichoderma isolate Th2 as well as guazatine, significantly (p = 0.05) increased plant dry weight compared with untreated pathogen-infested seeds. Suitability of in vitro methods to evaluate potential efficacy of antagonists as biocontrol agents is discussed. [ABSTRACT FROM AUTHOR]

Pyrenophora tritici-repentis (Died) Drechs. (anamorph=Drechslera tritici-repentis (Died) Shoem. is one of the most important and widespread necrotrophic pathogen of wheat in Argentina. Breeding, chemical treatments and appropriate cultural practices are the main ways for disease control. The possibility of biological control is added as a complementary strategy within the integrated management of the disease. Trichoderma spp. have been used as biocontrol agents to protect plants against soil-borne and foliar diseases in several crops. The objective of the present work was to evaluate the potential of Trichoderma harzianum (isolate Th15, Th11, Th2, Th81, Th7, Th13, Th8, Th5), Trichoderma aureoviride (isolate Ta1, Ta100) and Trichoderma koningii (isolate Tk11, Tk6) as biocontrol agents of D. tritici-repentis under in vitro and greenhouse conditions. Dual cultures in Petri dishes containing potato dextrose agar showed that the isolates of Trichoderma spp. tested inhibited significantly the mycelial growth of D. tritici-repentis between 50% and 74%. Microscopic examination of cultures of Trichoderma spp. and D. tritici-repentis in close proximity showed plasmolysis of conidia and hyphae of the pathogen. The results of the greenhouse tests in 2000 and 2001 indicated that seven strains of Trichoderma spp. (Th5, Th11, Th13, Tk6, Tk1, Th2 and Th81) significantly reduced the disease severity on wheat plants compared with untreated plants. In general, there was a significant decrease in Trichoderma spp. population on the wheat phylloplane with time. Additional greenhouse studies using other isolates and under a wide range of temperature conditions are needed to fully assess the potential and limitations of Trichoderma spp. as biocontrol agents of D. tritici-repentis. [Copyright &y& Elsevier]

The incidence, severity and progress of tan spot (Pyrenophora tritici-repentis) of wheat under different inoculum types were analysed during 2000 and 2001 in two different environments of Buenos Aires Province. Severity, incidence and area under the disease progress curve (AUDPC) were higher in 2001 than in 2000. Inoculum as spore pulverization treatments of Drechslera tritici-repentis occasioned higher disease severity than the application of oat grains colonized with the pathogen at low or high inoculum concentration. Severities increased with the growth stage of wheat plants. In both environments severity was higher when the evaluation was performed at 14 days compared to 7 days after inoculation. The combined analysis for incidence and severity showed significant differences between all main factors and the interactions except the quadruple for incidence and environment×evaluation date and environment×growth stage×evaluation date for severity. For the AUDPC all main factors and interactions were significant except environment×evaluation date. Due to the significant interactions with the environment both years were analysed separately. For the separate analysis, incidence, severity and AUDPC increased with the growth stage and evaluation date in both years. The severity and AUDPC increased for the spore pulverization treatment with respect to oat grain application. For incidence there were differences between both treatments only in 2000 environment. Furthermore, the highest rate of spore pulverization caused a higher severity and AUDPC than the lowest rate. However, there were no differences for incidence between doses. [Copyright &y& Elsevier]

During the conduction of health tests of barley seeds belonging to crops in Argentina, we observed colonies with the appearance of species in the genus Bipolaris. The organism was subsequently keyed to the specie Bipolaris zeicola based on morphological characteristics. This preliminary identification was confirmed by molecular characterization through an amplification of the internal transcriber spacer and glyceraldehyde-3-phosphate dehydrogenase. The fungal isolate was inoculated onto barley and maize seedlings and produced foliar symptoms in both cereals, producing typical symptoms on maize. The present identification constitutes the first report of Bipolaris zeicola on barley worldwide and the first citation of the presence of this pathogen on any host in Argentina. • Bipolaris zeicola is a pathogen common in maize and sorghum. • Bipolaris zeicola was reported for the first time on barley. • Bipolaris zeicola was reported for the first time on any hosts in Argentina. • Identity of the pathogen was confirmed through morphological and molecular analyses. [ABSTRACT FROM AUTHOR]