Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of
Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type
Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with
Glomus mosseae and
Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using
Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different
Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM
A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM
Azospirillum phytostimulators does not alter mycorrhization.
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