Effect of soil matric water potentials on germination of ascospores of Monosporascus cannonballus and colonization of melon roots by zoospores of Olpidium bornovanus

Abstract

Results document, for the first time, the role of soil moisture on a unique, tripartite, host-specific rhizosphere interaction (i.e., Cucumis melo-Monosporascus cannonballus-Olpidium bornovanus). Specifically, colonization of cantaloupe roots by zoospores of O. bornovanus and germination of ascospores of M. cannonballus were highest at a soil matric potential of −0.001 MPa but significantly inhibited at a matric potential of only −0.01 MPa. Matric water potentials of −0.01 MPa or drier are characteristically inhibitory to the motility of zoosporic microbes but not hyphal growth of filamentous fungi like M. cannonballus. These results support our previous conclusion that germination of ascospores of M. cannonballus, a destructive root pathogen of cantaloupe is mediated by O. bornovanus, an obligate, zoosporic fungus.