A fast method to evaluate in a combinatorial manner the synergistic effect of different biostimulants for promoting growth or tolerance against abiotic stress.

Background: According to the most popular definition, a biostimulant is any substance or microorganism applied to plants with the aim to enhance nutrition efficiency, abiotic stress tolerance and/or crop quality traits, regardless of its nutrient content. Therefore, a biostimulant can help crops to withstand abiotic stress, while maintaining or even increasing productivity. We have previously designed a sequential system, based on two different model organisms, the baker's yeast Saccharomyces cerevisiae and the plant Arabidopsis thaliana, to evaluate the potential of different natural extracts as biostimulants employing a blind-test strategy.

Results: In this report, we further expand this concept to evaluate different biostimulants in a combinatorial approach to reveal the potential additive, synergistic or antagonistic effects of different combinations of biostimulants in order to design new formulations with enhanced effects on plant growth or tolerance to abiotic stress. The method is based on yeast assays (growth tests in solid medium, and continuous growth in liquid cultures) and plant assays (mass accumulation in hydroponic culture) to assess effects on early growth.

Conclusions: With this novel approach, we have designed new formulations and quantified the ability to enhance growth and promote biomass accumulation under normal conditions and in the presence of abiotic stresses, such as drought, salinity or cold. This method enables a fast screen of many different products in a combinatorial manner, in order to design novel formulations of natural extracts with biostimulant potential.