Aceptando la existencia de un terreno inexistente en un problema matemático: el uso prevalente de argumentos pragmáticos por docentes de primaria

El presente estudio aborda los diferentes tipos de argumentaciones dados por 69 profesores de primaria para justificar la existencia (o inexistencia) de un terreno cuyo dibujo se encontraba en un problema propuesto en el libro de matemáticas de quinto grado de primaria en México. La tarea de los maestros no era resolver el problema sino argumentar acerca de la existencia real del terreno cuyas características numéricas son imposibles. La gran mayoría de los docentes aceptaron la posible existencia de dicho terreno, proporcionando diferentes tipos de argumentos. En este artículo se reportan los resultados de la categorización de estos argumentos. Todos los argumentos son de naturaleza pragmática, es decir, los docentes no formularon ningún argumento con sustento matemático. Aunque no debían resolver el problema diseñado para los alumnos, 44 profesores lo resolvieron. La característica más notable de sus respuestas es la ausencia de argumentos sobre las condiciones en que dichas respuestas son aceptables

Lyophilization as a method for pathogens long term preservation

Lyophilization (freeze-drying) is one of the most suitable methods used for a long term preservation of pathogens. The aim of this paper was the application of lyophilization for storage of three significant plant pathogens: Fusarium graminearum, Helminthosporium gramineum, and Pseudomonas syringae pv. gylicinea, respectively. The plant material was collected continuously (during a four year period 2002-2006), depending on a plant development stage, from different localities in Vojvodina. Pathogens were isolated from diseased parts with characteristic symptoms, and placed on nutritive media specific for a certain pathogen, using standard phytopathological methods. Lyophilization was carried out in marked and coded ampoules by freezing and drying of pathogen suspension and nutritive medium. Revitalization of lyophilized isolates was done after four days. High percentage of revitalization was characteristic for all studied isolates, and it ranged from 85-92%, confirming that lyophilized pathogens would be capable of keeping viability for a long time in the collection. Besides above mentioned pathogens, there were 200 isolates in the collection, originating mostly from field and vegetable crops. Each isolate that was put into the Collection, was followed by all the necessary data such as: name of the pathogen, number of isolates, locality, host plant year of isolation, name of the researcher and other relevant data

Impact of climatic conditions on outbreaks of bacterial spot on tomato and pepper caused by Xanthomonas vesicatoria and Xanthomonas euvesicatoria

Seed-borne bacterial pathogens of tomato and pepper are of major concern worldwide. Xanthomonas vesicatoria (Xv) and Xanthomonas euvesicatoria (Xe), the causal agents of bacterial leaf spot, and Clavibacter michiganensis subsp. michiganensis (Cmm), the causal agent of tomato bacterial canker, are worldwide distributed, but the occurrence of the latter is usually erratic. In order to evaluate the risk of seed transmission and the relationship between seed contamination and disease outbreak, an extensive field trial has been put in place in 2013 for each pathosystem. Three artificially contamination levels were considered, composed of 100 seedlings each. Disease outbreaks were weekly monitored during the growing season until harvesting and disease was quantified by means of AUDPC. Seeds were produced from each plot and analysed in order to assess their contamination level. Preliminary results of our studies showed that disease quantity caused by Xv, Cmm or Xe was directly correlated to the percentage of initial infection, according to AUDPC values obtained. Contamination rate of seed produced in diseased fields was not always correlated with disease quantity observed. A microbial consortium, a bacterial antagonist and a plant polyphenol were assayed to assess their potential efficacy in seed disinfection: naturally contaminated tomato and pepper seeds were treated and sown. Pepper and tomato seedlings were inspected and analysed for the presence of bacterial spot. Preliminary results obtained show that none of the above mentioned treatments was able to eradicate the pathogen from seeds

Diverzitet populacije Xanthomonas spp. patogena paprike u Srbiji

During 2008, 2009 and 2010 samples of diseased pepper leaves with bacterial spot symptoms were collected from different localities in Republic of Serbia. Total of 116 strains of bacteria were obtained by isolation from infected leaves. Studies of pathogenic, biochemical and physiological traits showed that tested strains belong to species Xanthomonas euvesicatoria. Two serological tests (DAS - ELISA and agglutination test) confirmed antigenic identity of tested bacterial isolates and serological similarity to bacteria X. c. pv. vesicatoria. Differentiation of Xantomonas spp. causal agent of bacterial spot of pepper was performed using two molecular methods. The first method was based on restriction analysis – RFLP (Restriction Fragment Length Polymorphism) of the hrp gene fragment (HrpB region) after digestion of obtained products by restriction enzymes (CfoI, TaqI and HaeIII). Comparison of restriction profiles of studied strains to control strains confirmed the similarity with the X. euvesicatoria. The other molecular method is polymerase chain reaction of specific primers which allow amplification of different size products sprecific for: X. euvesicatoria – 173 bp; X. vesicatoria – 138 bp; X. perforans – 197 bp and X. gardneri – 154 bp. As a result, DNA fragments of 173 bp which belong to species X. euvesicatoria were detected at all studied strains, including test strain Xe KFB (189). Threshold of detection was confirmed to be 0.4x103 CFU/ml. The effects of copper-sulphate (CuSO4), antibiotics streptomycin and kasugamycin on the development of bacterial cells were studied. The sensitivity of strains to bactericides was studied in vitro by culturing bacteria on sucrose pepton agar (SPA) plates, amended with filter-sterilized aqueous solution of streptomycin and kasugamycin (50, 100, 200 ppm) or copper-sulphate (100, 200 ppm). Streptomycin resistant strains were not detected, but 6 strains were resistant to kasugamycin (50 ppm) and 19 strains to copper-sulphate (200 ppm), indicating bacterial resistance development...Tokom 2008, 2009 i 2010. godine prikupljeni su uzorci obolelog lišća paprike sa simptomima bakteriozne pegavosti iz različitih lokaliteta Republike Srbije. Izolacijom iz zaraženih listova dobijeno je 116 sojeva bakterija. Proučavanja patogenih, biohemijsko-fizioloških odlika ukazuju da proučavani sojevi pripadaju vrsti Xanthomonas euvesicatoria. Primenom dva serološka testa (DAS - ELISA i test aglutinacije) potvrđena je antigena uniformnost proučavanih sojeva, kao i serološka sličnost sa bakterijom X. c. pv. vesicatoria. Diferencijacija Xanthomonas spp. prouzrokovača bakteriozne pegavosti paprike izvršena je primenom dve molekularne metode. Prvi metod zasnivao se na restrikcionoj analizi - RFLP (Restriction Fragment Lenght Polymorphism) fragmenta hrp gena (HrpB regiona) nakon digestije (sečenja) dobijenih proizvoda restrikcionim enzimima (CfoI, TaqI i HaeIII). Poređenjem restrikcionih profila proučavanih sojeva sa kontrolnim sojevima, potvrđena je sličnost sa vrstom X. euvesicatoria. Drugi molekularni metod je lančana reakcija polimeraze primenom specifičnih prajmera koji amplifikuju proizvode različite veličine specifične za: X. euvesicatoria – 173 bp; X. vesicatoria – 138 bp; X. perforans – 197 bp i X. gardneri – 154 bp. Kod svih proučavanih sojeva, uključujući i kontrolni soj X. euvesicatoria KFB (189) detektovani su fragmenti DNK veličine 173 bp, koji odgovaraju vrsti X. euvesicatoria. Utvrđeno je da je prag detekcije ove metode 0,4 x 103 CFU/ml. Proučeno je dejstvo bakar-sulfata (CuSO4), antibiotika streptomicina i kasugamicina, pri različitim koncentracijama, na razvoj bakterijskih ćelija u in vitro uslovima. U podlogu su dodati filterom sterilisani rastvori bakar-sulfata do konačne koncentracije od 100 i 200 ppm tj. aktivne komponente navedenih antibiotika do konačne koncentracije od 50, 100 i 200 ppm. Sojevi rezistentni na streptomicin nisu detektovani ovim istraživanjima. Rezistentnost prema 50 ppm kasugamicina utvrđena je kod 6 sojeva, a 19 sojeva je bilo rezistentno na 200 ppm bakar-sulfata. Dobijeni rezultati ukazuju na opasnost od razvoja rezistentnosti bakterija prema ovim jedinjenjima..

Planing for quality – organization and responsibillity for purchasing

Very few organizations are totally self – contained to the extent that their products andservices are all generated at one location, from basic materials. The total cost ofbought-in material and/or services usually forms a large proportion of the final sellingprice of an organizations products or services.Consequently,purchasing is anexstremely important, specialized function which should never be underestimated. Themake or buy decision refers to the problem encountered by an organization whendeciding whether a product or service should be purchased from outside sources orgenerated interlay. Often make or buy decisions and the suppliers are based on price,but this is a dangerous criterion with which to evaluate these strategic decisions.Purchasing is an important feature of just-in time (JIT) methods of inventory control.The development of long-term relationships with a faw suppliers, rather than short-termones with many, leads to the concert of coproduces in networks of trust providingdependable quality and delivery of goods and services. Each organization in the chainof supply is encouraged to extend JIT methods to its suppliers

Životna sposobnost i vigor semena različitih inbred linija kukuruza tretiranih neonikotinoidima

The aim of this study was to examine the effects of different neonicotinoid seed treatments on viability and vigour of maize (Zea mays L.) inbred lines. The trial included three maize inbred lines (207 x 312/5 DNS, 7-1 NS, and 312/5 DNS) treated with recommended doses of three commercial formulations of systemic insecticides (Poncho 600-FS, Gaucho 600-FS, and Cruiser 350-FS). Generally, formulation Gaucho 600-FS can be considered the most harmful regarding the impact on the reduction of germination in all tested maize inbred lines. A significant reduction of germination in maize inbred line 7-1 NS was observed after seed treatment with Cruiser 350-FS, using the standard germination test and cold test. A significant increase in seedlings root and shoot growth of maize inbred line 312/5 DNS treated with Poncho 600-FS and Cruiser 350-FS was noted using the cold test.Cilj ovog istraživanja je bio da se ispita uticaj različitih tretmana semena neonikotinoidima na životnu sposobnost i vigor semena inbred (Zea mays L.) linija kukuruza. Eksperimentalni objekti su bile tri različite inbred linije kukuruza (207 x 312/5 DNS, 7-1 NS i 312/5 DNS) tretirane sa tri komercijalne formulacije (Poncho 600-FS, Gaucho 600-FS i Cruiser 350-FS) u preporučenim dozama. Generalno se Gaucho 600-FS može smatrati štetnim pošto utiče na smanjenje klijavosti semena kod svih ispitivanih inbred linija. Značajno smanjenje klijavosti semena inbred linije 7-1 NS primećeno je nakon tretmana sa Cruiser 350-FS kod standarnog testa klijavosti i hladnog testa. Značajan porast korena i nadzemnog dela izdanaka inbred linije 312/5 DNS tretirane formulacijama Poncho 600-FS i Cruiser 350-FS je uočen primenom hladnog testa

Diversity of Xanthomonas spp. population - pepper pathogens in Serbia

Tokom 2008, 2009 i 2010. godine prikupljeni su uzorci obolelog lišća paprike sa simptomima bakteriozne pegavosti iz različitih lokaliteta Republike Srbije. Izolacijom iz zaraženih listova dobijeno je 116 sojeva bakterija. Proučavanja patogenih, biohemijsko-fizioloških odlika ukazuju da proučavani sojevi pripadaju vrsti Xanthomonas euvesicatoria. Primenom dva serološka testa (DAS - ELISA i test aglutinacije) potvrđena je antigena uniformnost proučavanih sojeva, kao i serološka sličnost sa bakterijom X. c. pv. vesicatoria. Diferencijacija Xanthomonas spp. prouzrokovača bakteriozne pegavosti paprike izvršena je primenom dve molekularne metode. Prvi metod zasnivao se na restrikcionoj analizi - RFLP (Restriction Fragment Lenght Polymorphism) fragmenta hrp gena (HrpB regiona) nakon digestije (sečenja) dobijenih proizvoda restrikcionim enzimima (CfoI, TaqI i HaeIII). Poređenjem restrikcionih profila proučavanih sojeva sa kontrolnim sojevima, potvrđena je sličnost sa vrstom X. euvesicatoria. Drugi molekularni metod je lančana reakcija polimeraze primenom specifičnih prajmera koji amplifikuju proizvode različite veličine specifične za: X. euvesicatoria – 173 bp; X. vesicatoria – 138 bp; X. perforans – 197 bp i X. gardneri – 154 bp. Kod svih proučavanih sojeva, uključujući i kontrolni soj X. euvesicatoria KFB (189) detektovani su fragmenti DNK veličine 173 bp, koji odgovaraju vrsti X. euvesicatoria. Utvrđeno je da je prag detekcije ove metode 0,4 x 103 CFU/ml. Proučeno je dejstvo bakar-sulfata (CuSO4), antibiotika streptomicina i kasugamicina, pri različitim koncentracijama, na razvoj bakterijskih ćelija u in vitro uslovima. U podlogu su dodati filterom sterilisani rastvori bakar-sulfata do konačne koncentracije od 100 i 200 ppm tj. aktivne komponente navedenih antibiotika do konačne koncentracije od 50, 100 i 200 ppm. Sojevi rezistentni na streptomicin nisu detektovani ovim istraživanjima. Rezistentnost prema 50 ppm kasugamicina utvrđena je kod 6 sojeva, a 19 sojeva je bilo rezistentno na 200 ppm bakar-sulfata. Dobijeni rezultati ukazuju na opasnost od razvoja rezistentnosti bakterija prema ovim jedinjenjima...During 2008, 2009 and 2010 samples of diseased pepper leaves with bacterial spot symptoms were collected from different localities in Republic of Serbia. Total of 116 strains of bacteria were obtained by isolation from infected leaves. Studies of pathogenic, biochemical and physiological traits showed that tested strains belong to species Xanthomonas euvesicatoria. Two serological tests (DAS - ELISA and agglutination test) confirmed antigenic identity of tested bacterial isolates and serological similarity to bacteria X. c. pv. vesicatoria. Differentiation of Xantomonas spp. causal agent of bacterial spot of pepper was performed using two molecular methods. The first method was based on restriction analysis – RFLP (Restriction Fragment Length Polymorphism) of the hrp gene fragment (HrpB region) after digestion of obtained products by restriction enzymes (CfoI, TaqI and HaeIII). Comparison of restriction profiles of studied strains to control strains confirmed the similarity with the X. euvesicatoria. The other molecular method is polymerase chain reaction of specific primers which allow amplification of different size products sprecific for: X. euvesicatoria – 173 bp; X. vesicatoria – 138 bp; X. perforans – 197 bp and X. gardneri – 154 bp. As a result, DNA fragments of 173 bp which belong to species X. euvesicatoria were detected at all studied strains, including test strain Xe KFB (189). Threshold of detection was confirmed to be 0.4x103 CFU/ml. The effects of copper-sulphate (CuSO4), antibiotics streptomycin and kasugamycin on the development of bacterial cells were studied. The sensitivity of strains to bactericides was studied in vitro by culturing bacteria on sucrose pepton agar (SPA) plates, amended with filter-sterilized aqueous solution of streptomycin and kasugamycin (50, 100, 200 ppm) or copper-sulphate (100, 200 ppm). Streptomycin resistant strains were not detected, but 6 strains were resistant to kasugamycin (50 ppm) and 19 strains to copper-sulphate (200 ppm), indicating bacterial resistance development..

Hlor-dioksid kao dezinficijens za kontrolu Ralstonia solanacearum u vodi, skladištu i opremi

Brown rot or bacterial wilt caused by bacterium Ralstonia solanacearum is the main limiting factor in potato production. Quarantine measures are necessary to avoid spread of disease to disease-free areas. R. solanacearum has been shown to contaminate watercourses from which crop irrigation is then prohibited causing further potential losses in yield and quality. The bacteria also spread via surfaces that diseased seed potatoes come into contact with. This study showed bactericidal activity of chlorine dioxide (CIO2) on R. solanacearum for disinfection of water, surface and equipment. The results showed that CIO2 solution at concentration of 2 ppm at 30 minutes of exposure time had bactericidal effect for disinfection of water. For surface and equipment disinfection, concentration of 50 ppm showed total efficacy at 30 min and 5 sec exposure time, respectively. Results suggest that use of CIO2 as a disinfectant has a potential for control of brown rot pathogen in water, storage and equipment.Mrka trulež ili bakteriozna uvelost krompira prozrokovana bakterijom Ralstonia solanacearum ograničavajući je faktor uspešne proizvodnje krompira. Sprovođenje karantinskih mera zaštite je neophodno kako bi se izbeglo širenje bakterije u regione u kojima bolest nije prisutna. S obzirom da R. solanacearum može kontaminirati vodene tokove i izvore koji služe za navodnjavanje useva, zabrana korišćenja dovodi do dodatnih potencijalnih gubitaka u prinosu i kvalitetu krompira. Bakterija takođe kontaminira površine sa kojima zaraženi semenski krompir dolazi u dodir. U ovom radu prikazana je baktericidna aktivnost hlor-dioksida (CIO2) na bakteriju R. solanacearum u cilju dezinfekcije vode, površine i opreme. Dobijeni rezultati pokazuju da CIO2 ispoljava baktericidni efekat za dezinfekciju vode u koncentraciji od 2 ppm nakon 30 minuta ekspozicije, za dezinfekciju površine u koncentraciji 50 ppm nakon 30 minuta ekspozicije i za dezinfekciju opreme u koncentraciji 50 ppm nakon 5 sekundi ekspozicije. Rezultati dobijeni u ovom radu ukazuju da CIO2 poseduje potencijal kao dezinficijens za kontrolu prouzrokovača mrke truleži krompira u vodi, skladištu i opremi

Ionic liquids as potentially new antifungal agents against Alternaria species

The fungal genus Alternaria Nees 1816 includes the most prevalent pathogenic species that can cause crop diseases such as blight, black spot, and dark leaf spot. In accordance with the aim of developing modern sustainable approaches in agriculture for the replacement of synthetic and toxic substances with environmentally friendly alternatives, the objective of this study was to examine thein vitro antifungal activities of 18 newly synthesized ionic liquids (ILs) against three Alternaria strains: A. padwickii, A. dauci and A. linicola. The antifungal activities of the ILs were estimated via a microdilution method to establish minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values. The results confirmed that 17 of the 18 ILs showed strain specificity, including good antifungal activity toward Alternaria strains, with MIC and MFC values in the range of 0.04 to 0.43 mol dm(-3). The strongest antifungal effects toward all analyzed Alternaria strains were displayed by the compounds with long alkyl chains: [omim][Cl] (MIC/MFC: 0.042 mol dm(-3)), [dmim][Cl] (MIC/MFC: 0.043 mol dm(-3)), [ddmim][Cl] (MIC/MFC: 0.053 mol dm(-3)), [ddTSC][Br] (MIC/MFC: 0.053 mol dm(-3)), and [Allyl-mim][Cl] (MIC/MFC: 0.054 mol dm(-3)). The introduction of oxygen as a hydroxyl group resulted in less-pronounced toxicity towards Alternaria compared to the introduction of an ether group, while the contribution of the hydroxyl group was shown to be a more determining factor than the prolongation of the side-chain, resulting in overall fungicidal activity decrease. Our results indicate the possibility that the most effective ILs ([Allyl-mim][Cl], [omim][Cl], [dmim][Cl], [ddmim][Cl], [bTSC][Br], [hTSC][Br], [oTSC][Br], [dTSC][Br], and [ddTSC][Br]) could be applied to the control of plant diseases caused by Alternaria species, based on their potential as an environmentally friendly crop protection approach. Since salts based on TSC cations are significantly cheaper to synthesize, stable under mild conditions, and environmentally friendly after degradation, thiosemicarbazidium-based ILs can be a suitable replacement for commercially available imidazolium ILs