Search Results - (Author, Cooperation:L. Bouwman)

2014-10-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Biodiversity ; *Conservation of Natural Resources ; *Extinction, Biological

1432-0789

Microcosm ; Arable soil ; Bacteria ; Bacterivorous nematodes ; Nematophagous fungi ; Carbon and nitrogen ; Mineralization

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract A microcosm experiment was carried out to quantify the effects of organisms at various trophic levels on C and N mineralization after the addition of crop residues to arable soil. The effects of the bacterivorous nematodes Rhabditis sp. and Acrobeloides bütschlii and of the nematophagous fungi Arthrobotrys oligospora und Drechmeria coniospora on soil respiration and N mineralization were measured over 6 months at 20°C. In the presence of nematodes, C mineralization was increased during the first month and subsequently reduced; N mineralization was increased during the first 2 months and then reduced. The results support the assumption that nematodes influence C mineralization mainly indirectly by affecting bacterial activity, and N mineralization mainly directly by mineralizing bacterial biomass. A. oligospora contributed directly to C mineralization. The effect of both fungi on N mineralization was indirect and resulted from the reduction in the numbers of nematodes. The results showed that the effects of nematodes and nematophagous fungi and the mechanisms behind the effects may vary strongly in time, and are correlated with the type of organic matter decomposed.

Electronic Resource

1432-1793

Springer Online Journal Archives 1860-2000

Biology

Abstract A simple, quantitative density separation method is described. The method is based on differences in specific weight between meiobenthos and sediment. Nematodes and copepods could be separated from sediment and detritus when samples were suspended in Ludox-TM, a colloidal silica. Organisms float at the surface, while sediment particles sink. Results obtained with this new method were compared with the well-known decantation method. For a quantitative isolation of nematodes from sediments, rich in coarse detritus, a maximum volume of 7 cm3 sample could be used. For copepods this maximum was 13 cm3. For such sediments the density method is more reliable than the decantation method. The time needed for sorting the meiobenthic organisms is reduced to about 30% compared with the former method. The new method can be used for preserved as well as for fresh sediment samples and can also be applied for the disolation of small polychaetes, small oligochaetes, larvae of some macrofaunal groups and net-zooplankton.

Electronic Resource

1573-5125

Springer Online Journal Archives 1860-2000

Biology

Summary The feeding strategies and feeding techniques of 12 nematode species, isolated from the Ems-Dollard estuary, were investigated in agar cultures. In the consumption of bacteria, algae, diatoms, protozoa and small metazoa, two main strategies are distinghuished: the non-selective strategy, characteristic of species living on the surface of macrophytes, and the selective strategy, characteristic of sediment-inhabiting species. The selective strategists showed various ingestion techniques, depending on the size and armature of the buccal cavity; food items could be ingested whole, or pierced or cracked and the contents sucked out.

Electronic Resource

1573-8469

Globodera rostochiensis ; G. pallida ; hybridoma ; PCR ; pathotypes ; RAPD ; 2D-gel electrophoresis ; virulence genes

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Efficient and accurate diagnostic assays are essential for the design and evaluation of control measures of the potato cyst nematodesGlobodera rostochiensis andG. pallida by means of resistance. The hybridoma technology and the polymerase chain reaction (PCR) offer in potential various possibilities to design such diagnostic tests for routine purposes. We set out to devise a refined advisory system based on biochemical assays by using the following stepwise approach. In the early 80's a research program was started to develop an immunoassay to differentiate the two sibling species of potato cyst nematodes. Species specific monoclonal antibodies were raised against nematode proteins which are thermostable, abundant and homologous, and which enable reliable species identification using single eggs. The second step to improve the management of virulence genes is aimed at discriminating groups of populations within a species (‘virulence groups’ or ‘pathotypes’). The concept is that the number of initial populations introduced from South America is limited and that numerous Dutch populations (‘secondary founders’) are closely related by descent. Biochemical characters revealed by two-dimensional gel electrophoresis (2-DGE) of polypeptides, PCR in combination with restriction enzyme digests and RAPD (Random amplified polymorphic DNA) will be used to delineate groups of populations. The final diagnostic assay will be based on PCR. One of the challenges will be to devise a manageable number of primers to recognize all distinct groups. The third research line is aimed at developing a PCR assay based on the virulence genes themselves. Genetic studies showed that virulence inG. rostochiensis towards the H1 resistance gene is inherited at a single locus and is recessive to avirulence. To identify molecular markers linked to the virulence gene, 300 virulent lines were selected via backcrossing the F1 (Aa) with the virulent (aa) parent line. Molecular differences between the parent lines were obtained by 2-DGE, RFLP's (restriction fragment length polymorphisms) and RAPD. Especially RAPD proved to be a valuable technique to construct a linkage map. Screening 80 primers (10-mer) resolved more than 120 markers. RAPD will eventually lead to flanking DNA sequences, which will be used to isolate and characterize the virulence gene. Sequence information of the virulence gene inG. rostochiensis for the H1 resistance gene can be used to devise primers for a PCR assay and may also provide a starting point to isolate other virulence genes.

Electronic Resource