Molecular defense response of mycorrhizal bean plants infected with Rhizoctonia solani

A time course study was conducted to investigate disease development and molecular defense response in common bean ( Phaseolus vulgaris L.) plants colonized by a mixture of five arbuscular mycorrhizal (AM) fungi, namely, Glomus mosseae , G. intraradices , G. clarum , Gigaspora gigantea , and Gigaspora margarita , and post-infected with the soil-borne pathogen Rhizoctonia solani . Results showed that pre-colonization of bean plants by AM fungi significantly reduced disease severity and disease incidence. DNA fingerprinting using the differential display technique revealed a genetic polymorphism (86.8 %) in bean plants that resulted from the colonization by AM fungi. Two genetic mechanisms were recorded: (1) switching on of new genes and (2) induction of other active genes, including the defense genes chitinase and β-1,3-glucanase, to a highly expressed state.