BAREA, JOSÉ-MIGUEL, CONCEPCIÓN AZCÓN-AGUILAR& ROSARIO AZCÓN.
Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Prof. Albareda 1,18008 Granada, SPAIN.
Due to the importance of AM associations in the context of rhizosphere ecology,it has been proposed that either the AM fungi or the AM symbiosis be usedas a target biosafety model system concerning the reliable application of microbial inoculants whenreleased at the soil-plant interfaces, particularly for inocula fromgenetically modified microorganisms. For these purposes a series ofexperiments are being carried out to compare the effects on AM formation and function of a wild type (WT) Rhizobium meliloti strain with those of its genetically modified(GM) derivative. This GM Rhizobium was developed to improve the nodulation competitiveness of the WT strain.It was found that such rhizobial strain did not interfere with any of aseries of processes related to mycorrhiza formation by G.mosseae. Indeed, the GM Rhizobium increased the number of AM colonization units and the nutrient acquisition ability in mycorrhizal plant. In otherexperiments, Pseudomonas spp., used in "biological control", producing the antifungal compound 2, 4-diacetylphloroglucinol (DAPG)were tested for their effects on AM fungi. The results from in vitro and in soil assays showed a lack of any negative effect of these Pseudomonas strains on spore germination, and even a stimulation of hyphal growth of Glomus mosseae. Soil microcosm experiments demonstrated that these bacteria produced a significant increase in the percentage of the root system becoming mycorrhizal. These and other case studies will be discussed in the context of mycorrhiza/bacteria interactions for their sustainable management as biofertilizers and biocontrol agents.