The effects of plant growth-promoting rhizobacteria (PGPR) on the growth and quality of strawberries

Several studies have shown the benefits of plant growth-promoting rhizobacteria (PGPR) on plant mineral nutrition, suggesting their possible application as biofertilizers. PGPR can stimulate plant growth, increase plant resistance to abiotic and biotic stresses and might thus have a positive effect on fruit quality. The aim of this research was to evaluate and compare the effects of beneficial microorganisms, supplied either as pure culture (Azospirillum brasilense) or as a commercial mixture (Effective Microorganisms - EM T), on the growth and quality of strawberry (Fragaria ananassa 'Elsanta') fruits. Strawberry frigo-plants were hydroponically grown either in a complete nutrient solution, or in a nutrient solution inoculated with A. brasilense or with EM for 10 weeks. At harvest, biometric parameters, such as shoot and root fresh weights, and yield parameters, like number of fruits plant(-1) and fruit weight, were recorded. Growth parameters (e.g., biomass, leaf area) were not affected by the rhizobacteria. Even though PGPR-inoculated plants showed slightly reduced fruit yields in terms of average number of fruits plant(-1), they delivered larger fruits as compared to untreated control. Fruits obtained from PGPR-inoculated plants also had a higher sweetness index in comparison to control fruits. The content of total phenols showed no significant difference between the different samples, whereas the concentration of flavonoids and flavonols was higher in fruits harvested from A. brasilense-inoculated plants. In addition, PGPRs also influenced the uptake and allocation of nutrients in fruits, in particular increasing the concentration of micronutrients.