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Ecology and Epidemiology

Rhizosphere Competence of Fusarium Species Colonizing Corn Roots. Cynthia M. Ocamb, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Current address: USDA Forest Service, North Central Forest Experiment Station, 1992 Folwell Ave., St. Paul, MN 55108; Thor Kommedahl, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 84:166-172. Accepted for publication 30 November 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-166.

We examined colonization of corn roots and rhizosphere soil by Fusarium species, corn root and rhizosphere colonization by Fusarium graminearum in competition with F. oxysporum or F. proliferatum in the growth chamber, and variability in corn root and rhizosphere colonization among isolates of F. graminearum and F. oxysporum. When corn kernels were infested with individual Fusarium species then planted in the field, F. moniliforme, F. oxysporum, and F. proliferatum were isolated from root tissue and rhizosphere soil along the entire portion of root sampled. F. solani was isolated from nearly the entire root length and accompanying rhizosphere soil. F. equiseti and F. graminearum, however, were isolated from a very limited portion of the root and rhizosphere soil. Colonization patterns in a growth chamber were similar to the field study. Moreover, F. graminearum colonized a smaller portion of the root and rhizosphere in the presence of F. oxysporum or F. proliferatum than alone. Isolates of F. graminearum and F. oxysporum varied in degrees of root and rhizosphere colonization. We suggest that F. moniliforme, F. oxysporum, F. proliferatum, and F. solani are rhizosphere competent on corn, whereas F. graminearum and F. equiseti are not rhizosphere competent.