Seedlings of Fragaria × ananassa Duch var. Elyana F1 with continuous flowering habit, were transplanted in plastic pots (400 mL) in a soil (Brill Ortopack, Agrochimica, Bolzano, Italy; pH 5.5-6.5) previously sterilized by flowing steam (101℃ for 1 h), and kept in a greenhouse for rooting. After 1 month, they were transplanted in new plastic pots (900 mL) in a 2/1 v/v mixture of sterile soil (the same used in the first transplant) and sand (sterilized in oven at 180℃ for 3 h), and inoculated or not with one of three different AMF in combination with one of three different bacterial strains . Plants were initially irrigated 3 times per week. When the plants began to produce fruits, they were transplanted again in plastic pots of 3 L capacity. Starting from 1 week after the last transplant, they were irrigated daily: once per week with a Long Ashton (LA) nutrient solution , and with tap water on the other days. In particular, half of the control plants (C) were watered with LA 32 µM phosphate, while the remaining controls (C-P) and all the inoculated plants were fed with LA 16 µM phosphate until harvest. Strawberry plants were maintained in greenhouse for 16 weeks.The arbuscular mycorrhizal fungus Rhizophagus irregularis (Ri) (DAOM197-198) was provided by INRA (Recorbet and Bernaud, Dijon). Funneliformis mosseae (Fm) (BEG12) was provided by the European Bank of Glomales (Dijon). Septoglomus viscosum (Sv), collected from an Italian soil (Tuscany, Italy), was produced and provided by Mybasol S.r.l. (Alessandria, Italy). The three inocula, prepared as a mixture of soil, mycorrhizal roots, hyphae, and spores, were mixed (11% v/v) with the plant growth medium.Pseudomonas fluorescens strain Pf4 (Pf4) was isolated from a forest soil located in Sassello (Savona, Italy) and characterized by Berta et al. . Pseudomonas sp. 5Vm1K (5Vm) was isolated from the rhizosphere of blueberry plants grown in a larch woodland (Bellino, Cuneo, Italy) and characterized as described by Bona et al. . P. fluorescens strain 19Fv1t (19Fv) was provided by Mybasol s.r.l (Alessandria, Italy) and characterized by Bona et al. . Bacterial 16S rDNA sequences were deposited in the NCBI database GenBank with the accession numbers KF234076, KF233995, KF752592 for Pf4, 5Vm, and 19Fv, respectively.Bacterial cells were grown on tryptic soy agar (TSA) at 28℃ for 48 h and suspended in 0.1M MgSO₄. Bacterial density (600 nm) was adjusted to 10⁹ CFU/mL. Each plant was inoculated with 8 mL of bacterial suspension, except uninoculated ones that were irrigated with the same quantity of MgSO₄. After 1 week the plants were inoculated again.

In general, AMF mostly affected the parameters associated with the vegetative portion of the plant, while plant growth promoting bacteria (PGPB) were especially relevant for fruit yield and quality. The plant physiological status was differentially affected by inoculations, resulting in enhanced root and shoot biomass. Inoculation with Pf4 bacterial strain increased flower and fruit production per plant and malic acid content in fruits, while decreased the pH value, regardless of the used fungus. Inoculations affected fruit nutritional quality, increasing sugar and anthocyanin concentrations, and modulated pH, malic acid, volatile compounds and elements.