The biocontrol effect of mycorrhization on soilborne fungal pathogens and the autoregulation of the AM symbiosis: One mechanism, two effects?

Abstract

The establishment of the AM in the roots of more than 80% of all land plants is the result of a complex exchange of signals between the host plant and AMF. Many reports are available that once the AMF has penetrated the host root and established its interradical organs of nutrient exchange between the AMF and the plant, a number of physiological and morphological changes occur in the host plant. In recent years, it has been reported that once plants are colonized by AMF, further root colonization by AMF is regulated (reviewed by Vierheilig 2004a,b). In analogy to the rhizobial autoregulatory mechanism in legume plants, this phenomenon with AMF has been named autoregulation of mycorrhization. Recently, it has been suggested that the bioprotective effect of mycorrhization and the autoregulation of mycorrhization are possibly two sides of the same coin. It seems plausible that an already mycorrhizal plant develops just one mechanism to repulse further colonization by fungi, not discriminating between AMF and soilborne pathogenic fungi (Vierheilig and Piché 2002; Vierheilig 2004a,b).