Effect of arbuscular mycorrhizal fungus Glomus mosseae and Bacillus subtilis on the infection of tomato roots by Fusarium oxysporum

Abstract

Two biocontrol agents, i.e. arbuscular mycorrhizal fungus (AMF) Glomus mosseae, and a plant growth-promoting rhizobacteria (PGPR) Bacillus subtilis (BS) were tested separately and together for suppression of Fusarium oxysporum f. sp. lycopersici (FOL) on tomato plants, under greenhouse conditions. Infestation of soils with FOL drastically reduced plant growth parameters (root and shoot length, number of branches, number of leaves, fresh and dry weights of roots and shoots) and increased the root / shoot ratios, compared to non-infested ones. However, the detrimental effects caused by FOL infestation were less detected in G. mosseae and/or B. subtilis inoculated treatment. G. mosseae and B. subtilis enhanced also the nutrient content (N, P, K, Ca, Mg, Fe and Zn) of the infected plants and the pigment content of their leaves, particularly in dual inoculation of the two microorganisms. Treatment with single or mixture of the two biocontrol agents reduced disease severity by 85-93.4 %. The pathogen reduced root colonization by the mycorrhizal fungus, however, the presence of B. subtilis increased the percentage of colonization. G. mosseae and / or B. subtilis reduced, however, the percentage of fusarium infection in tomato roots. The antagonistic potential of the local isolate of B. subtilis against F. oxysporum was also tested in laboratory experiment. The highest antagonistic potential was also obtained after seven days of inoculation (66%). Image Analysis System revealed interaction between B. subtilis and the pathogen (FOL) led to a series of disturbances including disorganization of the fungal cytoplasm, malformation of hyphae of the pathogen, cell wall lysis as well as the disappearance of pathogen conidia.