Wheat Root Exudate and Early Stages of Infection by Helminthosporium sativum Pamm., King and Bakke

THE observations of Flentje et al. 1,2 on Corticium solani led them to the hypothesis that the morphology of hyphal infection structures at the host surface may depend on a chemical stimulus contained specifically in host root exudate and not only on the physical stimulus of contact 3 . Evidence produced recently by de Silva and Wood 4 refutes this hypothesis. Working again with C . solani and the closely allied C. praticola they report that infection structures can be induced both with and without root exudate in a non-specific manner. Clearly this topic needs further examination, especially with other fungal genera. One recent report of another source of chemical stimulus supports Flentje's hypothesis. Guttation fluid, according to Endo et al. 5,6 , stimulates the formation of infection structures of Helminthosporium sorhinianum on plastic slides, these structures being rare or absent in tap water and distilled water controls.