Attachment of bean rust cell wall material to host and non-host plant tissue

A preparation of bean rust (Uromyces phaseoli) germ tube walls, consisting of short, filamentous particles, was labeled with fluorescein iso-thiocyanate. Freeze sections of host and non-host tissue were incubated in the labeled preparation. Maximum staining was observed in host plant tissue (Phaseolus vulgaris), in which bean rust regularly forms haustoria. In tissue of the non-host plantsVigna sinensis andPhaseolus lunatus, where fewer haustoria were formed, staining was only weak. However, no staining was observed in the non-host tissue ofPhaseolus aureus, Helianthus annuus, Brassica oleracea andHordeum vulgare in which the infection hypha did not form haustoria. This would appear to indicate that formation of haustoria is induced by a specific attachment of the hyphal wall to the host wall. The possibility that elicitors attach in a similar way, is discussed.