Interactions among Glomus irregulare, arbuscular mycorrhizal spore-associated bacteria, and plant pathogens under in vitro conditions

Abstract

Arbuscular mycorrhizal (AM) fungi interact with bacteria (AM fungi-associated bacteria, AMB) in the mycorrhizosphere. We previously identified a set of AMB that enhance AM fungal colonization, plant growth, and inhibit pathogens. Here, we used transformed carrot root cultures in a two-compartment plate system for further in vitro studies on interactions taking place among Glomus irregulare (syn.Glomus intraradices), AMB, and plant pathogens. We found that exudates of G. irregulare stimulated growth of all ten AMB isolates tested in multi-well plates. AMB growth stimulation was observed also during co-cultivation of three of these AMB with G. irregulare in the hyphal compartment. In addition, co-cultivation stimulated growth of G. irregulare hyphae and spore production, as well as G. irregulare root colonization. GC/MS analysis in a preliminary screening of metabolites revealed differences in concentrations of several identified but also unidentified compounds in G. irregulare hyphal exudates. Exudates in presence of three different AMB isolates co-cultivated with G. irregulare contained several additional compounds that differed in amount compared with G. irregulare alone. The results indicate that G. irregulare exudates contain carbohydrates, amino acids, and unidentified compounds that could serve as a substrate to stimulate AMB growth. With regard to effects on plant pathogens, growth inhibition of Rhizoctonia solani, Verticillium dahliae, and Pectobacterium carotovorum ssp. carotovorum was evident in the presence of the AMB isolates tested together with the G. irregulare exudates. These in vitro studies suggest that G. irregulare and AMB stimulate growth of each other and that they together seem to provide an additive effect against growth of both fungal and bacterial pathogens.

Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack

“…While non-mycorrhizal fungi might have colonised plant roots and contributed to the transfer of signalling compounds, this is unlikely because AM fungi often antagonise soil pathogenic fungi (e.g. Bharadwaj et al 2012;Campos-Soriano et al 2012;Jung et al 2012) and the bean roots were confirmed to contain abundant arbuscules, which are specific to AM fungi. Moreover, bridges between plants formed by AM fungi can be established both by hyphal growth from one plant to another and by anastomosis where two hyphae of the same isolate fuse together and exchange nuclei.…”

Arbuscular mycorrhizal fungi stimulate organic phosphate mobilization associated with changing bacterial community structure under field conditions

“…It seems likely that the microbiome attached to the hyphae was not associated with hyphal biomass but with hyphal exudates and suggests that different AMF may release different exudates. The composition of AMF hyphal exudates mainly consists of sugars, carboxylates and amino acids (Bharadwaj et al, 2012;Zhang et al, 2016), but how this differs from plant root exudates and between AMF species needs to be studied. Understanding the interaction between specific hyphal exudates and recruitment of PSB will be critical to allow us to manipulate the system effectively (Zhang et al, 2016).…”

Possible Roles of Rhizospheric and Endophytic Microbes to Provide a Safe and Affordable Means of Crop Biofortification

“…R12, the selenium level in the grains was improved compared to inoculating with either of the bacteria alone [45]. Besides, mycorrhizae also excrete H + and low-molecular weight organic chelating compounds, such as citric acid, oxalic acid, and siderophores, to solubilize Fe in soil [151]. Recently, mycorrhizal inoculation in wheat roots was reported to have increased the uptake of P, Fe, and Zn by the plant, along with greater root length and density [44].…”