Using the European Biostimulant Industry Council definition, a plant biostimulant means a material that contains substance(s) and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and/or crop quality, independently of its nutrient content.
The probiotic bacteria used in commercial probiotic solutions are naturally occurring plant-associated microorganisms that enhance the growth of the host plants including yield, and may suppress diseases when applied in adequate amounts. Plant growth promoting probiotic bacteria include Bacillus, Paraburkholderia, Pseudomonas, Acinetobacter, Alcaligenes, Arthrobacter, and Serratia. Probiotic bacteria help host plants through the production of phytohormones, antibiotics and lytic enzymes, fixation of atmospheric nitrogen, solubilization of soil mineral nutrients, and induction of systemic resistance in the host plants.
In a scientific article published in Nature (link), researchers demonstrated that two probiotic bacteria not only significantly increased growth and fruit yield but also enhance the functional properties of strawberry by inducing enhanced production of total antioxidants, carotenoids, flavonoids, phenolics and anthocyanins. They also found that another two naturally occurring probiotic bacteria isolated from the native environment could be used for sustainable production of high quality strawberries with no or little additional use of expensive synthetic inputs.