VIEW ARTICLE

Biochemistry and Cell Biology

Growth of Rhizosphere Competent and Incompetent Fusarium Species from Corn on Carbon Substrates. 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 84:508-514. Accepted for publication 12 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-508.

The ability of Fusarium isolates that are rhizosphere incompetent or competent on corn to grow on types of carbon common in the rhizosphere was examined in culture. When growth of Fusarium species was evaluated on glucose, pectin, carboxymethyl cellulose, microcrystalline cellulose, xylans, or xylose, F. graminearum produced a significantly greater hyphal dry weight than did F. equiseti, F. moniliforme, F. oxysporum, F. proliferatum, or F. solani, whereas F. graminearum produced fewer conidia than did the other species. Intraspecific variation in growth occurred among isolates of F. graminearum, F. oxysporum, and F. proliferatum. When F. graminearum was paired with F. moniliforme, F. oxysporum, or F. proliferatum, the numbers of macroconidia and colony-forming units of F. graminearum were lower than those obtained from cultures of F. graminearum grown alone. F. moniliforme, F. oxysporum, and F. proliferatum generally yielded no difference in conidial or colony-forming unit production when in dual culture with F. graminearum as when cultured singly. These data suggest that F. graminearum is less competitive than or is suppressed by F. moniliforme, F. oxysporum, and F. proliferatum and, therefore, could not be rhizosphere competent.