Pre-symbiotic and symbiotic interactions between the arbuscular mycorrhizal (AM) fungus Glomus intraradices and two Paenibacillus species associated with AM intraradical mycelia and spores.

L FERNANDEZ; V. SILVANI; M. PERGOLA; A. GODEAS

SOIL BIOLOGY AND BIOCHEMISTRY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Nueva York; Año: 2011 vol. 43 p. 1866 - 1872

0038-0717

Two indole-producers Paenibacillus species, intimately associated with propagules of arbuscular mycorrhizal (AM) fungi, were examined for their mycorrhization helper bacteria activity at pre-symbiotic and symbiotic stages. The effects were tested under In Vitro and In Vivo conditions using an axenically propagated strain of G. intraradices as AM fungus model. The rates of spore germination and re-growth of intraradical mycelium were not affected by inoculation of Paenibacillus strains in spite of the variation of indole production measured in the bacterial supernatants. Alternatively, a clear promotion in the pre-symbiotic mycelium development occurred after inoculation of both bacteria under In Vitro conditions. The P. rhizosphaerae strain TGX5E significantly increased the extraradical mycelium network, the rates of sporulation, and the root colonization in the In Vitro symbiotic association. These results were also observed in the rhizosphere of soybean plants grown under greenhouse conditions, when P. rhizosphaerae TGX5E was co-inoculated. Nevertheless, the soybean dry biomass production was not associated with the increased development and infectivity values of G. intraradices. P. favisporus strain TG1R2 caused suppression on the parameters evaluated of G. intraradices during In Vitro symbiotic stage, but not under In Vivo condition. The extraradical mycelium network produced and the colonization of soybean roots by G. intraradices were promoted compared to the control treatments. In addition, dual inoculation had a promoting effect on soybean biomass production. In summary, species of Paenibacillus frequently associated to AM fungus structures in the soil, may have a promoting effect on short term pre-symbiotic mycelium development, and little impact on AM propagules germination. This could be an explanation to the particular associations found between some bacterial strains and AM fungus propagules; but this promotion could not necessarily persist along the symbiotic stage. Some of our results obtained using the axenic system could be extrapolated to the soil condition, where the plant growth promoting effect of bacteria could also collaborate with the host growth and AM symbiosis development.