Behaviour of Phytophthora cinnamomi Zoospores on Roots of Australian Forest Species

Abstract

Twenty-three species from Australian native forests were examined in a comparative assay of the chemotaxis of zoospores of Phytophthora cinnamomi towards their roots. Zoospores were attracted to all species tested when within 3-4 mm from the roots. Attraction to wounds and cut ends of roots was also observed. The chemotaxis was neither species-specific nor host-orientated. The root zone which attracted most zoospores was the region of elongation for most species, but this varied and is described and illustrated for the different species. Encysted zoospores produced one and occasionally two germ tubes which were normally orientated towards the root axis. Subsequent penetration of epidermis, cortex and vascular tissue was observed and, like the chemotaxis and chemotropy, was not related to host susceptibility.