MULCHES AND OTHER COVER MATERIALS TO REDUCE WEED GROWTH IN CONTAINER-GROWN NURSERY STOCK.

Due to the recent EU-wide implementation of Integrated Pest Management (IPM), alternative methods to reduce weed growth in container-grown nursery stock are needed to cut back the use of herbicides. Covering the upper layer of the substrate is known as a potential method to prevent or reduce weed growth in plant containers. As a high variety of mulches and other cover materials are on the market, however, it is no longer clear for growers which cover material is most efficient for use in containers. Therefore, we examined the effect on weed growth of different mulches and other cover materials, including Pinus maritima, P. sylvestris, Bio-Top Basic, Bio-Top Excellent, coco chips fine, hemp fibres, straw pellets, coco disk 180LD and jute disk. Cover materials were applied immediately after repotting of Ligustrum ovalifolium or planting of Fagus sylvatica. At regular times, both weed growth and side effects (e.g., plant growth, water status of the substrate, occurrence of mushrooms, foraging of birds, complete cover of the substrate and fixation) were assessed. All examined mulches or other cover materials were able to reduce weed growth on the containers during the whole growing season. Weed suppression was even better than that of a chemical treated control. Although all materials showed some side effects, the impact on plant growth is most important to the grower and depends not only on material characteristics (e.g., biodegradation, nutrient leaching and N-immobilisation) but also on container size and climatic conditions. In conclusion, mulches and other cover materials can be a valuable tool within IPM to lower herbicide use. To enable a deliberate choice of which cover material is best used in a specific situation more research is needed on lifespan and stability as well as on economic characteristics of the materials.

Immunological characterization of the leukemic megakaryocytic line at light and electron microscopic levels.

Twenty cases of leukemia involving platelet precursors have been identified by a panel of monoclonal and polyclonal antiplatelet antibodies and by the ultrastructural demonstration of platelet peroxidase (PPO). The two techniques were in close agreement both for identification and for the quantitation of the blast cells except in three cases where PPO was present in the absence of the immunological markers. The immunological appearance of the leukemic megakaryocytic precursors was identical to that of their normal counterparts; the cells were positive with J 15 (anti GP IIb-IIIa complex), C 17 (anti GP IIIa), J 2 (anti GP 26,000) AN 51 (anti GP Ib). A diffuse cytoplasmic labelling was observed with anti factor VIII vwF and anti platelet factor 4 (PF 4). In addition, the leukemic maturation was quite similar to normal megakaryocyte differentiation since in micromegakaryocytes the expression of Gp Ib was strong and an intense granular pattern of labelling with anti factor VIII vwF and anti PF 4 was observed. In no case was the leukemic megakaryocytic series labelled by anti-erythroid antibodies, anti myeloid antibodies or J 5, B 1, OKT 11 antibodies. Using ultrastructural immunoferritin with J 15 it was possible to demonstrate that labelling with this antibody only occurred on PPO-positive cells. Immunogold or peroxidase labelling with AN 51 at the EM level in cases of mixed leukemia showed that Gp Ib was absent from proerythroblasts and myeloblasts. Therefore, in no case were specific platelet markers expressed in the leukemias of other cell lineages.