Quinoxyfen--resistance management and sensitivity monitoring in wheat: 1995-2000

Wheat powdery mildew, Blumeria (= Erysiphe) graminis DC f sp tritici Marschal is one of the most important foliar diseases of cereals in Europe, and has shown a high potential for adaptability in sensitivity towards modern fungicides during the last 20 years. Quinoxyfen is a surface-mobile fungicide from a new chemical class that has been commercially used for the control of B graminis in Europe since 1997. When the compound was launched, a Resistance Management Strategy was implemented which included: no seed treatments, no autumn use, a specified window of application and recommendations for appropriate tank-mixing. To assess the success of this Management Strategy, a European-wide resistance monitoring programme was carried out between 1995 and 2000 using spore trap sampling, and a whole plant assay. The mean EC50 values found by year were 0.060 mg litre-1 in 1995, 0.052 mg litre-1 in 1996, 0.071 ml litre-1 in 1997, 0.039 mg litre-1 in 1998, 0.039 mg litre-1 in 1999 and 0.063 mg litre-1 in 2000. No new sensitivity classes were found. The slight shift to lower sensitivity in 1998 and 1999 was correlated with similar shifts in three wildtype isolates, and was ascribed to experimental variation. The monitoring programme will continue to assess the long-term impact of the management recommendations on the resistance status of quinoxyfen.     

Estimating water retention curves of forest soils from soil texture and bulk density

Forest soils differ significantly from the arable land in their distribution of the soil bulk density and humus content, but the water retention parameters are primarily derived from the data of agricultural soils. Thus, there is a need to relate physical parameters of forest soils with their water retention characteristics and compare them with those of agricultural soils. Using 1850 water retention curves from forest soils, we related the following soil physical parameters to soil texture, bulk density, and C content: air capacity (AC), available water capacity (AWC), and the permanent wilting point (PWP). The ACs of forest soils were significantly higher than those of agricultural soils which were related to the low bulk densities of the forest soils, whereas differences in AWCs were small. Therefore, for a proper evaluation of the water retention curves (WRCs) and the parameters derived from them, further subdivisions of the lowest (< 1.45 g cm^‐3) of the three bulk density classes was undertaken to the wide range of low soil densities in forest soils (giving a total of 5 bulk density classes). In Germany, 31 soil texture classes are used for the estimation of soil physical parameters. Such a detailed classification is not required because of insignificant differences in WRCs for a large number of these classes. Based on cluster analysis of AC, AWC, and PWP parameters, 10 texture collectives were obtained. Using 5 classes of bulk densities, we further calculated the ACs, AWCs, and the PWPs for these 10 classes. Furthermore, “van Genuchten parameters” (θ r, θ s, α, and n) were derived which described the average WRC for each designated class. In a second approach using multiple regression analysis, regression functions for AC, AWC, and PWP and for the van Genuchten parameter were calculated.     

Use of microcalorimetry to study microbial activity during the transition from oxic to anoxic conditions

Microbial heat production is a nonspecific measure for microbial activity irrespective of O₂ availability in soils. In a series of long-term batch microcalorimeter experiments with closed ampoules, we examined the microbial activity in glucose-amended soil aggregates from different soil depths of a clay forest soil during the transition from aerobic to anaerobic conditions. Furthermore, the influence of the soil aggregate size on the long-term metabolic heat production was examined. Heat output curves showed a distinct pattern for soil samples from different soil depths and aggregate sizes and led to the following conclusions: 1. Microbial biomass and microbial activity strongly decreased with increasing soil depth as well as increasing soil aggregate size despite relatively constant organic C concentrations. 2. The transition from aerobic to anaerobic conditions led to a considerable drop in microbial activity. However, based on the energy balance, 10-26% of the heat production during the aerobic phase is attributable to anoxic or partly anoxic metabolism. 3. After O₂ exhaustion, a lag phase of low but constant heat output was observed, followed by a peak of anaerobic metabolic activity. Heat production during the lag phase was hypothesised to be an indicator for the biomass of facultatively anaerobic microorganisms in the soil.     

Über die Einwirkung heterotropher Mikroorganismen auf die Zersetzung silikatischer Minerale

The effect of heterotrophic microorganisms upon the degradation of silicate minerals The purpose of the present work was to study the weathering activity of yeasts and filamentous fungi on various silicate minerals. Culture experiments were carried out on samples of amphibolite, biotite, and orthoclase. Finely ground powder was incubated with pure cultures of 5 yeast strains and 11 filamentous fungi in a glucose-mineral salts-solution at room temperature over a period of 12 weeks. Changes in pH as well as in concentrations of K, Ca, Mg, Fe, Al, and Si in the culture solutions were determined at various intervals.-All fungal strains tested lowered the pH of the culture liquid with or without minerals added from 5.7 to values as low as 1.6. This acidification was brought about by the microbial production of organic acids, especially of gluconic acid. The lowest pH values were found in flasks containing biotite. Acidification in flasks with orthoclase was less pronounced. The pH values found in flasks containing amphibolite were similar to those produced in cultures without mineral powder. From biotite, up to 62% K, 33% Mg, 29% Fe, 59% Al, and 6% Si were released. The solubilizing activity on orthoclase was less effective, and least that on amphibolite.-The importance of acidity and the chelating capacity of the microbially produced organic acids as well as the chemical and structural properties of the mineral with respect to weathering are discussed. The results show that heterotrophic microorganisms like yeasts and filamentous fungi may effectively attack silicate minerals and rocks.     

Ergebnisse von Simulationsrechnungen mit einem Bodenstickstoffmodell zur Düngung und zum Zwischenfruchtbau in Trinkwasserschutzgebieten

Results of computer simulations on fertilization and catch cropping problems in water protection areas by means of a soil nitrogen model A simple model of the nitrogen turnover in soil is presented. The model was validated by field experiment time series. The simulation results showed that dividing of the mineral nitrogen fertilization during spring for root crops or maize as well as shortening the first spring nitrogen fertilization for winter cereals diminished the leaching of nitrate only in extremely wet springs on sandy soils. The great importance of winter catch cropping in a cereal-root crop or a cereal-maize rotation on all soils and the necessity to avoid liquid manuring during late summer and early autumn, especially on sandy soils without catch cropping, are demonstrated. The results underline the predominant influence of the weather conditions on nitrate leaching.     

Methicillin‐Resistant Staphylococcus aureus (MRSA) in Three Dairy Herds in Southwest Germany

The objective of this study was to analyse the occurrence of methicillin‐resistant Staphylococcus aureus (MRSA) in three dairy herds in the southwest of Germany that had experienced individual cases of clinical and subclinical mastitis associated with MRSA. The herds were identified by the detection of MRSA during routine resistance testing of mastitis pathogens. All quarters of all cows in the herds that were positive on California Mastitis Test were sampled for bacteriological analysis on two occasions. Bulk tank milk samples were also tested. Furthermore, nasal swabs were collected from people working on the farms and from cattle. Environmental samples were collected from associated pig holdings. Isolates were characterized using spa‐typing and testing for antimicrobial resistance. Our results revealed a substantial spread of MRSA in the three dairy herds. In the first of the two investigations carried out on all cows in the three herds, milk samples of 5.1–16.7% of dairy cows were found positive for MRSA. The respective proportions in the second herd level investigation were 1.4–10.0%. Quarters harbouring MRSA had higher somatic cell counts than quarters that were negative on culture. Methicillin‐resistant Staphylococcus aureus were also detected in nasal swabs of staff (7/9), cows (7/15) and calves (4/7), bulk tank milk samples (3/3) and environmental samples from pig premises (4/5) on the farm. Herds B and C had no contact to herd A. However, in all three herds MRSA of spa‐type t011 were detected in milk samples. Results show that MRSA of spa‐type t011 is a problem in dairy farms that needs urgent attention.     

QTL for delayed bolting after winter detected in leaf beet (Beta vulgaris L.)

Growing sugar beet (Beta vulgaris L. ssp. vulgaris) as a winter crop in cool temperate climates is expected to increase yield potential. However, this requires bolting resistance after winter. One strategy to achieve complete bolting resistance is to accumulate genes for bolting delay from various genetic resources within the B. vulgaris gene pool. To identify such genes, a QTL mapping was performed in a segregating population derived from a biennial leaf beet with delayed bolting after winter. The population was tested for bolting delay after winter in two different experiments with natural or artificial vernalization. Three QTL for bolting delay were mapped on linkage groups 3, 5 and 9 affecting bolting time by up to 19 days. These QTL could be combined with recently reported bolting QTL to develop a winter sugar beet with complete bolting resistance.     

Chromosome location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L.) 1. Mlk and other alleles at the Pm3 locus

Summary Several wheat cultivars/lines were inoculated with isolates of Erysiphe graminis tritici to identify new genes/alleles for resistance. The wheats were tested with 13 isolates that had been characterized from responses on differential lines with known resistance genes. Gene Mlk which occurs in cultivars Kolibri, Syros, Ralle and several other European common wheats was found to be an allele at the Pm3 locus and is now designated Pm3d. The mildew resistance in an old Australian wheat, W150, is conferred by a single gene also allelic to Pm3 and now designated Pm3e. The near-isogenic line Michigan Amber/8^*Cc possesses another allele now designated Pm3f. A Syrian land variety of common wheat shows mildew resistance that is conditioned by the combination of genes Pm1 and Pm3a. Finally, two accessions of Triticum aestivum ssp. sphaerococcum appeared to possess the Pm3c allele.