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In order to preserve environmental quality, alternative strategies to chemical-intensive agriculture are strongly needed. In this study, we characterized in vitro the potential plant growth promoting (PGP) properties of a gamma-proteobacterium, named MIMR1, originally isolated from apple shoots in micropropagation. The analysis of the 16S rRNA gene sequence allowed the taxonomic identification of MIMR1 as Luteibacter rhizovicinus. The PGP properties of MIMR1 were compared to Pseudomonas chlororaphis subsp. aurantiaca DSM 19603(T), which was selected as a reference PGP bacterium. By means of in vitro experiments, we showed that L. rhizovicinus MIMR1 and P. chlororaphis DSM 19603(T) have the ability to produce molecules able to chelate ferric ions and solubilize monocalcium phosphate. On the contrary, both strains were apparently unable to solubilize tricalcium phosphate. Furthermore, the ability to produce 3-indol acetic acid by MIMR1 was approximately three times higher than that of DSM 19603(T). By using fluorescent recombinants of strains MIMR1 and DSM 19603(T), we also demonstrated that both bacteria are able to abundantly proliferate and colonize the barley rhizosphere, preferentially localizing on root tips and in the rhizoplane. Finally, we observed a negative effect of DSM 19603(T) on barley seed germination and plant growth, whereas MIMR1, compared to the control, determined a significant increase of the weight of aerial part (+22 %), and the weight and length of roots (+53 and +32 %, respectively). The results obtained in this work make L. rhizovicinus MIMR1 a good candidate for possible use in the formulation of bio-fertilizers.

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Gallus cultures of two susceptible Castanea sativa cultivars, 'Garrone rosso' and 'Glone 71' were grown on culture medium supplemented to 50% with culture filtrates (GEs) from E4 virulent (E4-V) or E13 hypovirulent (E13-H) Cryphonectria parasitica strain, respectively. E13-H GEs caused a reduction in fresh weight and an increase in dry weight on calli of both genotypes. E4-V GEs did not induce any modification of these parameters compared with the control, but fresh weight of 'Glone 71' was reduced. Eight and electron microscopy observation showed the presence of large osmiophilic aggregates in the vacuoles and, sometimes, the ruptured tonoplast in the E4-V treated calli. Galli grown on E13-H GEs had a meristematic-like appearance, with small, scarcely vacuolated cells containing altered mitochondria and plasmaletnma proliferations.