Antifungalna aktivnost hitosana prema Alternaria alternata i Colletotrichum gloeosporoides

Chitosan and its derivatives have been reported as a promising alternative for control of postharvest fungal pathogens. The objective of this study was to evaluate in vitro and in situ antifungal activity of chitosan against Alternaria alternata and Colletotrichum gloeosporioides isolated from decayed apple fruits. The fungi were tested in vitro using PDA medium with three concentrations of chitosan (1, 2 and 3 mg/ml). Fungal growth of the test pathogens was significantly affected by all chitosan doses (P lt 0.05) after 7 days of incubation at 25°C. Water solution of 3 mg/ml of chitosan inhibited completely the conidial germination of A. alternata and C. gloeosporioides after 18 h incubation at 25°C. The results obtained from biocontrol assay indicate that the inhibition of postharvest decay of A. alternata and C. gloeosporioides was significantly influenced by chitosan concentrations. Disease incidence in chitosan-treated fruit after 7 days incubation at 25°C was significantly lower than in the positive control for both fungi tested (P lt 0.05). A. alternata and C. gloeosporioides used in this study were progressively inhibited in vitro and in situ with increasing concentrations of chitosan from 1 to 3 mg/ml.Istraživanja pokazuju da su hitosan i njegovi derivati dobra alternativa u kontroli skladišnih fitopatogenih gljiva. Cilj ovog rada bio je da ispita antifungalnu aktivnost hitosana prema Alternaria alternata i Colletotrichum gloeosporoides, izolovanih sa inficiranih plodova jabuke, u in vitro i in situ uslovima. Rast gljiva je testiran in vitro koristeći PDA podlogu sa različitim koncentracijama hitosana (1, 2 i 3 mg/ml). Porast oba patogena je bio značajno smanjen (P lt 0.05) u svim koncentracijama hitosana nakon 7 dana inkubacije na 25°C. Vodeni rastvor hitosana koncentracije 3 mg/ml je u potpunosti inhibirao klijanje konidija A. alternata i C. gloeosporoides nakon inkubacije od 18 sati na temperaturi od 25°C. Rezultati ogleda in situ ukazuju da inhibicija propadanja plodova inficiranih sa A. alternata i C. gloeosporoides zavisi od koncentracije rastvora hitosana. Pojava bolesti na plodovima jabuka tretiranih rastvorom hitosana nakon 7 dana inkubacije na 25°C bila je značajno smanjena za obe vrste gljiva (P lt 0.05) u odnosu na pozitivnu kontrolu. Rast A. alternata i C. gloeosporoides je bio progresivno inhibiran in vitro i in situ sa povećanjem koncentracije rastvora hitosana, od 1 do 3 mg/ml

Polyphasic identification of decay agents of lemon fruits in Serbia

Lemon fruits are an important source of vitamin C, potassium, folate, carotenoids, polyphenols, coumarins and terpenes. These lemon compounds have antioxidant and anti-inflammatory properties which have beneficial effects on human health. This re- search aimed to elucidate the etiology of blue and green molds detected on lemon fruits in Serbia. Using integrative identification approach, the obtained isolates were characterized from morphological, physiological, molecular, phylogenetic and pathological aspects. Col- ony growth and morphology were examined on Czapek yeast autolysate agar (CYA), Malt extract agar (MEA) and Creatine sucrose agar (CREA), and on CYA at two additional incu- bation temperatures (5 and 37 °C). For molecular identification, ITS and partial β-tubulin (BenA) genes were sequenced. Phylogenetic relationships were investigated using maximumlikelihood method. A pathogenicity test was carried out and the possible difference in pathogenicity among isolates was assessed with analysis of variance (ANOVA) and subsequent Tukey’s test. Four species were identified: Penicillium expansum, Penicillium digitatum, Penicillium polonicum and Talaromyces rugulosus. All four species proved to be pathogenic on lemon fruits, producing symptoms similar to those observed on naturally infected fruits. The results of this study are the first records of the beforementioned Penicillium/ Talaromyces species as postharvest pathogens on lemon fruits in Serbia and the first world report of T. rugulosus as phytopathogenic on the same host

In vitro efekat kalcijumovih soli na gljivične skladišne patogene

In the recent years, several studies have shown that calcium salts may have potential as environmentally compatible, nontoxic fungicides for controlling postharvest fungal patho­gens. Therefore, the objective of this study was to evaluate and compare the effects of calcium chloride and calcium hydroxide on in vitro mycelial growth, spore germination and germ tube growth of Colletotrichum acutatum, C. gloeosporioides, Alternaria alternata, and Penicillium expansum. The obtained results showed that the fungal isolates grew sim­ilarly or stimulated in the presence of 1 and 1.5% calcium salts compared to the control. After seven days of incubation, reduction of mycelial growth was observed only on PDA supplemented with 2% calcium salts. Calcium chloride and calcium hydroxide at 1.5% and 2.0% concentrations significantly decreased spore germination and germ tube growth of all fungal isolates. The results of this study show that the tested calcium salts can be used as a alternative treatment against postharvest fungal pathogens C. acutatum, C. gloeosporioides, A. alternata and P. expansum.Tokom poslednjih nekoliko godina, više studija je pokazalo da u kontroli gljivičnih skladišnih patogena soli kalcijuma mogu imati potencijal kao ekološki kompatibilni, netoksični fungicidi. Stoga je cilj ovog istraživanja bio da se u in vitro uslovima procene i uporede efekti kalcijum hlorida i kalcijum hidroksida na porast micelije, klijavost konidija i rast klicine cevi gljiva C. acutatum, C. gloeosporioides, A. alternata, i P. expansum. Dobijeni rezultati su pokazali da je u prisustvu 1 i 1,5% kalcijumovih soli porast izolata gljiva u tretmanima sličan ili povećan u odnosu na kontrolu. Nakon 7 dana inkubacije, redukcija porasta micelije je utvđena samo na PDA podlozi sa 2% soli kalcijuma. Kalcijum hlorid i kalcijum hidroksid u koncentracijama od 1,5 i 2,0% značajno smanjuju klijavost konidija i rast klicinih cevi svih ispitivanih izolata gljiva. Rezultati ove studije pokazuju da se testirane soli kalcijuma mogu primeniti kao alternativni tretman u kontroli gljivičnih skladišnih patogena, C. acutatum, C. gloeosporioides, A. alternata i P. expansum

Numerical modelling of concrete-filled steel tubular short columns under axial compression

The paper presents three-dimensional numerical models of short concrete-filled steel tubular circular columns that can successfully describe the column behaviour under axial compression. Several of the most commonly used material models for the steel part and a concrete portion of the column are evaluated in the models. In addition, the paper presents a new proposal for the extension of the Eurocode 2 stress-strain relation to make it suitable for describing the complex behaviour of concrete inside the steel tube. This model overcomes the current limitations of the Eurocode 2 design guide, referring to the limitation for the concrete curve in compression to 3.5‰ strain. The ultimate axial column strength obtained by the proposed model is compared to the ultimate column capacity calculated by a simplified method provided in Eurocode 4. All presented numerical models are validated on a set of experiments from the literature and demonstrate good agreement. The comments about the accuracy of each model are provided, along with the identified limitations

Postharvest decay of mandarin fruit in Serbia caused by Penicillium expansum

Mandarin fruits are one of the most popular among the Citrus genus. They are consumed because of their nutritional and health benefits, as well as pleasant taste and smell. This paper describes the identification and characterization of Penicillium expansum, isolated from molded mandarin fruits. The obtained isolates were cultivated on five media [Czapek Yeast Autolysate agar (CYA), MEA (Malt extract agar), Creatine sucrose agar (CREA), Yeast extract sucrose agar (YES), and Oatmeal agar (OA)] and at five different incubation temperatures (5, 15, 25, 30, and 37 °C). Isolates were sequenced for two molecular loci: internal transcribed spacer and beta-tubulin. Based on the results from morphological, physiological, molecular, and phylogenetic analyses, the recovered isolates were identified as P. expansum. The isolated species was confirmed as pathogenic to mandarin fruits in a pathogenicity test. To the best of our knowledge, this is the first report of P. expansum as a postharvest pathogen of mandarin fruit in Serbia

The Stiffness Matrix of the Fixed-End Composite Frame Element

The displacement method of frame analysis involves determination of the element stiffness matrix. In the paper, the stiffness matrix of the fixed-end composite frame element (type “k”) is derived. In general, the composite section consists of concrete part, steel section, reinforcing and prestressing steel. Concrete is considered as an aging, linear viscoelastic material. The relaxation of the prestressing steel is taken into account. The derived expressions can be used with any creep function and, also, for elements with variable cross-sections. The derivation of the element stiffness matrix follows two different approaches. The first approach is based on the integral stress-strain relation for concrete. The linear integral operators are used. In the second approach, the element flexibility matrix and the resisting force vector are determined through the numerical integration of the cross- section deformations. The class of cross-sections which accounts for viscous effects of a composite section is developed. The results of the two approaches are compared in the numerical example

Effects of Creep and Shrinkage on Deflections of Continuous Composite Beams

Creep and shrinkage of concrete affect the behavior of steel-concrete composite beams and should be taken into account in the analysis of these structures. A number of methods which have different level of accuracy are available for the time analysis of composite structures. Eurocode 4, the contemporary European code for design of steel- concrete composite structures, recommends simple methods for calculation of creep and shrinkage effects. In this paper, the deflections of continuous composite beams calculated with method proposed by Eurocode 4 and the more accurate Age Adjusted Effective Modulus Method (AAEM) are compared. Cracking of concrete is also considered. Through a set of numerical examples, accuracy of methods proposed by Eurocode 4 is discusse

Accuracy Evaluation of Creep and Shrinkage Calculation Methods According to EC4

In the paper, the creep and shrinkage calculation methods for composite steel-concrete beams are presented. The approximate methods AAEM, EM and methods according to Eurocode 4, as well as, the exact method based on the integral relation between stress and strain for concrete are used. For doubly-clamped composite beam, stresses at characteristic points of the cross-section for permanent loading and shrinkage effects are determined. Using the creep limit functions for concrete, the upper and lower limits for stresses are determined. According to these limits, the accuracy of the methods for creep and shrinkage calculation given in EC4 is evaluated

Fiber konačni element u nelinearnoj analizi kvadratnih spregnutih CFT stubova

The paper presents nonlinear analysis of square CFT columns using distributed plasticity fiber elements. Behaviour of CFT columns is nonlinear and it is necessary to include different nonlinear effects into the numerical model in order to simulate their behaviour properly. Model proposed in this work considers: nonlinear behaviour of concrete and steel using nonlinear stress-strain models, confinement effect and geometrical nonlinearities. Tests exposed to static loading with different slenderness, different D/t ratio (where D is the total dimension of a cross section and t is the thickness of steel tube) and different loading conditions are analyzed. Stress-strain models that best approximate the behaviour of CFT columns are determined from a detailed parametric study. The proposed numerical model is validated by comparing numerical with experimental results available in the literature.U radu je prikazana nelinearna analiza kvadratnih CFT stubova, pomoću fiber konačnog elemenata raspodeljene plastičnosti. CFT stubove karakteriše nelinearno ponašanje, što je potrebno imati u vidu u numeričkom modelu. Model predložen u ovom radu uzima u obzir sledeće nelinearne uticaje: nelinearno ponašanje betona i čelika primenom odgovarajućih konstitutivnih relacija, efekat utezanja betona i geometrijske nelinearnosti. Analizirani su uzorci izloženi delovanju statičkog opterećenja koji imaju različitu vitkost, odnos D/t (odnos ukupne dimenzije čeličnog profila [D] i debljine čeličnog profila [t]), kao i uzorci izloženi različitim tipovima naprezanja. Na osnovu parametarske analize, određeni su modeli materijala za čelik i beton, kao i njihovi parametri koji najbolje aproksimiraju ponašanje CFT stubova. Tačnost modela proverena je zatim i upoređivanjem sa eksperimentalnim podacima dostupnim u literaturi

Resistance of Composite Column to Compression and Bending

Design of the composite steel-concrete columns subjected to compression and bending, according to Eurocode 4, is shown in the paper. The effects of imperfections in the axial compression are taken into account indirectly by using the relevant European buckling curves. When a composite column is subjected to combined axial compression and bending, the analysis includes an increase in bending moment due to second order effects. The verification of the column resistance to compression and bending is based on the use of interaction curve. For the cross sections of fully encased columns with the I steel sections, very practical sets of continuous interaction curves are given. The curves are constructed for different composite column dimensions, steel sections and concrete classes