Motile spores of the phytopathogen Phytophthora cinnamomi are chemotactically attracted to the roots of potential host plants. We have observed that after approaching the root, the zoospores become aligned so that their ventral surface faces the root. This alignment is maintained as the flagella are detached and the cell becomes immobile. Adhesion of the spore to the root ensues rapidly and is a result of the secretion of adhesive material from internal stores confined to the cytoplasm beneath the ventral surface. The germ tube emerges from this same surface and grows straight towards the root. Thus, both adhesion and the orientation of germ tube outgrowth are clearly dependent on the correct alignment of the zoospores at the root surface.
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Hardham et al. (1990) studied this question.