Strategies for administration of biosurfactants-producing pseudomonads in closed hydroponic systems

Zoospore-producing oomycetes are major plant pathogens of particular concern in hydroponic systems. Compared with pesticides, biocontrol using antagonistic microorganisms is a sustainable approach to control oomycetes. Previous research has demonstrated that biosurfactants and biosurfactant-producing microorganisms are potentially useful components of a sustainable biocontrol strategy. In this study three ways of supplying a biosurfactant-producing strain to a recirculating hydroponic cultivation system infected with a zoospore-producing plant pathogen were evaluated. The strain P. koreensis 2.74 was added as washed cells, in its spent KB broth or in a minimal medium adapted from the nutrient solution, and compared with control treatments. A significant reduction in disease with up to 50% was achieved when a high concentration of washed cells was added weekly to the plant cultivation system. The disease suppression obtained through addition of washed cells equalled the effect achieved when the purified biosurfactant was used. Phytotoxicity was observed when the spent broth was included in the treatment

Jordtrötthet

Jordtrötthet är ett samlingsbegrepp för den försämrade tillväxten som uppstårvid återplantering av en rabatt, ett fält e.d. med samma eller ett närbesläktat växtslag. Den har ödesdigra ekonomiska konsekvenser för fruktodlingar och plantskolor. Problematikenharfrämst rapporterats och undersökts för växter tillhörande familjen rosväxter, Rosaceae, men det finns även indikationer på att andra växtslag kan drabbas, t.ex. pioner. Forskning för att lösa denna gåta har pågått i olika delar av världen i mer än 200 år utan att man egentligen har kommit till klarhet. Under det senaste decenniet har forskningen kring jordtrötthet enbart upprätthållits vid några enstaka forskningsstationer. Nya metoder och framsteg inom utvecklingen av biologiska bekämpningsmedel har gett upphov till nya vyerinomjordtrötthetsforskningen

Utilisation of Carbon Sources by Pythium, Phytophthora and Fusarium Species as Determined by Biolog® Microplate Assay

This study examined the metabolic activity of pure cultures of five root pathogens commonly found in closed hydroponic cultivation systems (Phytophthora cryptogea (PC), Phytophthora capsici (PCP), Pythium aphanidermatum (PA), Fusarium oxysporum f.sp. radicis-lycopersici (FORL) and Fusarium solani (FS)) using sole carbon source utilisation in order to develop effective biocontrol strategies against these pathogens. Aliquots of 150 µL of the mycelial suspension were inoculated in each well of GN2 microtitre plates. On the basis of average well colour development and number of positive wells, the pathogens were divided into two groups, (i) PA and FORL and (ii) PC, PCP and FS. Group (i) was characterised by a short lag-phase, a rapid exponential phase involving almost all carbon sources offered and a long stationary phase, while group (ii) had a more extended lag-phase and a slower utilisation rate of the carbon sources offered. The three isolates in group (ii) differed significantly during their exponential phase. The lowest utilisation rate of carbon sources and number of sources utilised was found for PCP. Of the major group of carbon sources, six carbohydrates, three carboxylic acids and four amino acids were rapidly used by all isolates tested at an early stage. The carbon sources gentibiose, α-D-glucose, maltose, sucrose, D-trehalose, L-aspartic acid, L-glutamic acid, L-proline persisted to the end of the exponential phase.Moreover, similarities between the metabolic profiles of the tested pathogen and the those of the resident microflora could also be found. These findings are of great importance as regards the role of the resident microflora in the biocontrol

Patterns of fungal and bacterial carbon mineralization across northern european peatlands

The fungal and bacterial activity was determined in 20 northern European peatlands ranging from ombrotrophic bogs to eutrophic fens with key differences in degree of humification, pH, dry bulk density, carbon (C) content and vegetation communities using the selective inhibition (SI) technique. These peatlands were partly disturbed and the respective water tables lowered below the surface layer. Basal respiration ranged from 24 to 128 mu g CO2-C g(-1) dry peat d(-1). Bacterial contributions to CO2 production were high in most peatlands and showed the following pattern: eutrophic >> transitional mesotrophic >> ombrotrophic peatland types. The fungal-to-bacterial (F:B) ratios varied substantially within peatland type, and this was mainly attributed to differences in peat botanical compositions and chemistry. The computed mean Inhibitor Additivity Ratio (IAR) was quite close to 1 to suggest that the SI techniques can be used to partition eukaryotic and prokaryotic activity in wide range of peatlands. Overall, basal respiration, microbial biomass-C, fungal and bacterial activities varied across the studied peatland types, and such differences could have consequences for C- and nutrient-cycling as well as how bogs and fens will respond to environmental changes

Ledningstal och mikronäringsämnen kan påverka effekt av biologisk bekämpning

Växtnäring tycks inte enbart ha effekt på växternas utveckling utan även på hur väl biologisk bekämpning fungerar. Undersökningar i Alnarp visar bland annat på ökad effekt av Binab T mot algsvampen Pythium ultimum vid ledningstal 2,5 eller högre i näringslösningen i slutna odlingssystem

Cool fruits - Effekter av lagringstid samt lagringstemperatur på förekomst av Listeria monocytogenes i färsk fruktcocktail

Färska fruktsallader (fruktcocktail) efterfrågas av konsumenter. Med dagens ansträngda elpriser ställs frågan om kyltemperaturen under framställning, transport och display i butiken skulle kunna höjas från 4 till 8 °C utan att äventyra livsmedelssäkerheten för dessa produkter. Föreliggande rapport bygger på en litteraturstudie och en provokationsstudie, där den köldtoleranta (psykrofila) organismen Listeria monocytogenes användes som modellorganism. Litteraturstudien genomfördes som en systematisk litteratursökning i databasen Web‐of‐Science. I den experimentella delen studerades tillväxtbeteendet av L. monocytogenes med hänsyn till lagringstemperatur och lagringstid i en färsk fruktcocktail bestående av ananas, röda äpplen, nätmelon och röda druvor. Den experimentella delen byggde på frågeställningen om lagringstemperaturen kan höjas från 4 °C till 8 °C samt från en rekommenderad lagringslängd på 4 dagar till 8 dagar, med hänsyn till förekomst av L. monocytogenes. En klinisk stam av L. monocytogenes inokulerades i färdiga råa fruktsallader. Tre temperaturregimer tillämpades: 4 °C i åtta dagar, 8 °C i åtta dagar samt 4 °C i ett dygn följt av 8 °C under återstående lagringstid på totalt åtta dagar (så kallad dynamisk temperaturregim). Vi fann att modellorganismen hade förökat sig efter åtta dagars lagringstid i samtliga behandlingar, dock avsevärt långsammare vid lagring i 4 °C, jämfört med kontinuerlig lagring i 8 °C samt den dynamiska behandlingen. Vid 4 °C lagringstemperatur visade L. monocytogenes en tillväxtpotential av knappt ett halvt log‐värde, samt med log 1,37 respektive log 1,23 vid 8 °C lagringstemperatur respektive dynamisk lagring, trots att fruktsalladens pH låg under minimi‐kraven för L. monocytogenes. I synnerhet i behandlingarna med högre temperatur förekom en massiv uppförökning av jästsvampar. Utifrån föreliggande resultat av litteraturundersökningen förordar vi ingen förhöjning av lagringstemperatur eller förlängning av lagringstid

Hygienization aspects of composting

• Compost use in agriculture always brings about the risk of introducing plant and human pathogens. • The backbone of the hygienization process consists of temperature, moisture content and chemical compounds formed during composting and activity of antagonists. • Compost produced by proper composting, i.e. a process that produces high temperatures during asufficiently long thermophilic phase can be applied safely. • Farmers should invest in good relationships with compost producers

Commercial wash of leafy vegetables do not significantly decrease bacterial load but leads to shifts in bacterial species composition

Production of leafy vegetables for the “Ready-to-eat”-market has vastly increased the last 20 years, and consumption of these minimally processed vegetables has led to outbreaks of food-borne diseases. Contamination of leafy vegetables can occur throughout the production chain, and therefore washing of the produce has become a standard in commercial processing. This study explores the bacterial communities of spinach (Spinacia oleracea) and rocket (Diplotaxis tenuifolia) in a commercial setting in order to identify potential contamination events, and to investigate effects on bacterial load by commercial processing. Samples were taken in field, after washing of the produce and at the end of shelf-life. This study found that the bacterial community composition and diversity changed significantly from the first harvest to the end of shelf-life, where the core microbiome from the first to the last sampling constituted <2% of all OTUs. While washing of the produce had no reducing effect on bacterial load compared to unwashed, washing led to a change in species composition. As the leaves entered the cold chain after harvest, a rise was seen in the relative abundance of spoilage bacteria. E. coli was detected after the washing indicating issues of cross-contamination in the wash water