CHARACTERIZATION OF SOIL ORGANISMS INVOLVED IN THE DEGENERATION OF AMMOPHILA-ARENARIA

The degeneration of Ammophila arenaria (marram grass) in stable stages of coastal foredunes may be due to pathogenic or parasitic soil organisms. To test this, and to characterize the organisms involved, biocides were applied to sand collected from the root zone of natural stands of A. arenaria. Seedlings of A. arenaria were grown and biomass production was measured and compared with growth of seedlings in γ-irradiated soil to determine effects of applied biocides. Sand from stable and mobile foredune sections (degenerated and vigorous A. arenaria, respectively) was examined. Improved seedling growth followed fungicide and ncmaticide treatments m sand from stable, as well as from mobile foredunes. On the other hand, bactericides (streptomycin and penicillin) had no effect. The fungicide propamocarb only stimulated growth very weakly, whereas the fungicide benomyl increased growth significantly. However, the effect of benomyl may not be solely due to its fungiddal action, as it also prevented root infection by the nematodes Heterodera (avenae group) and Meloidogyne maritima. The highest increase in yield was obtained with the nematicide oxamyl, which prevented root-infection by endo-parasitic nematodes (Heterodera avenae group, M. maritima and Pratylenchus sp.). Oxamyl also reduced numbers of ecto-parasitic nematodes. It is concluded that plant parasitic nematodes could be important in the degeneration of A. arenaria, but that interactions with other groups of soil organisms, such as soil fungi, cannot be excluded. © 1990.