Exudate molecules initiating fungal responses to seeds and roots

Abstract

Plant pathogenic fungi survive in soils in a quiescent state. In order for many root-pathogen interactions to be initiated, dormant propagules must be activated by molecules present in seed and root exudates. Without the release of such stimulatory molecules, the majority of root infections do not occur. Currently, little is known about the specific molecules involved in stimulating propagule germination and initiating root-pathogen interactions. Although certain molecules can be shown to elicit germination responses in vitro, responses of propagules reared on conventional culture media do not always reflect the responses of those formed on plant tissues in soil. Consequently, it is not possible to extend conclusions from laboratory determinations of the role of specific exudate molecules in stimulating fungal propagule germination to soil systems. The interaction of Pythium species with germinating seeds has served as a model system to answer questions about propagule behavior and the role of exudate stimulant molecules in establishing root-fungus interactions. The potential role of both volatile and water-soluble molecules in stimulating propagule germination are discussed.