Effects of soil fungi and nematodes on growth and nodulation of Hippophae rhamnoides (HR) were studied by treatment of sand dune soils with benomyl, propamocarb or oxamyl, and by inoculation. Frankia nodulation was greatly enhanced by benomyl in natural HR soil, but not in sterilized soil. The dominant fungi in the roots and rhizosphere of HR were Cylindrocarpon destructans and Fusarium oxysporum . Their infection percentages strongly decreased in the benomyl treatment. Oxamyl increased fungal infection of roots and rhizoplane, but had no or a positive effect on nodulation and shoot growth. Hence, plant parasitic nematodes appear to be a prerequisite for damage by fungi. Inoculation in sterilized sand showed that only some Cylindrocarpon isolates were slightly pathogenic. Results of this study suggest that soil fungi may decrease the vigour of HR, especially at sites where availability of N and Frankia are both limiting.
