Biocontrol of Fusarium root rot in the common bean (Phaseolus vulgaris L) by using symbiotic Glomus mosseae and Rhizobium leguminosarum

The interaction between VA mycorrhiza Glomus mosseae (Gm), root rodulating symbiont Rhizobium leguminosarum (R1), and root rot pathogen Fusarium solani (Fs) on the common bean (Phaseolus vulgaris) in relation to plant growth, nutrient uptake, disease severity, rhizosphere microbial biomass, and nutrient availability was investigated. Mycorrhizal plants yielded significantly greater plant biomass and mobilized more N and P uptake as compared to nonmycorrhizal plants or those infected with Fs. However, the mycorrhizal root colonizing ability, in presence of Fs, was reduced by 27%, whereas R1 enhanced it by 37%. The inoculation of Gm, besides decreasing propagule number of Fs in the rhizosphere, decreased pathogenic root rot by 34 to 77%. However, in the presence of R1, Gm-inoculated plants were more tolerant of the fungal root pathogen. The Gm + R1 inoculated plants not only had maximum plant biomass and root nodulation, but also exhibited higher microbial biomass, alkaline phosphatase activity, and available phosphorus in their rhizosphere. R1, alone or in association with Gm, caused the maximum increase in mineral nitrogen (NH4+ and NO3-) content in soil. These results indicate that Gm has a vital role in inhibiting the root pathogen from invasion, more so in the presence of R. leguminosarum.