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Quantification of Fusarium solani f. sp. phaseoli in Mycorrhizal Bean Plants and Surrounding Mycorrhizosphere Soil Using Real-Time Polymerase Chain Reaction and Direct Isolations on Selective Media

First and third authors: Department of Plant Science, McGill University, Macdonald Campus, 21, 111 Lakeshore, Raymond Bldg, Ste-Anne-de-Bellevue, QC, Canada, H9X 3V9; and second author: Institut de recherche en biologie végétale, Université de Montréal and Jardin botanique de Montréal, 4101 Sherbrooke Street East, Montréal, QC, Canada, H1X 2B2

The capacity of the arbuscular mycorrhizal fungus Glomus intraradices in reducing the presence of Fusarium solani f. sp. phaseoli in bean plants and the surrounding mycorrhizosphere soil was evaluated in a compartmentalized experimental system. Quantification of the pathogen and the symbiont in plant tissues, the soil regions of the mycorrhizosphere (rhizosphere and mycosphere), and the bulk soil was accomplished using specific polymerase chain reaction (PCR) primers in real-time PCR assays, culture-dependant methods, and microscopic determination techniques. Nonmycorrhizal bean plants infected with the pathogen had distinctive Fusarium root rot symptoms, while infected plants previously colonized by G. intraradices remained healthy. The amount of F. solani f. sp. phaseoli genomic DNA was significantly reduced in mycorrhizal bean plants and in each mycorrhizosphere soil compartment. The presence of G. intraradices in the mycorrhizosphere was not significantly modified, although the mycorrhizal colonization of roots was slightly increased in the presence of the pathogen. The results suggest that the reduced presence of Fusarium as well as root rot symptoms are caused by biotic and/or abiotic modifications of the mycorrhizosphere as a result of colonization with G. intraradices.

Additional keywords: LightCycler, Phaseolus vulgaris, SYBR Green.