In the last decades, with the constant increase in world population, the fast reduction of fertile arable land and the deteriorating environmental conditions, optimization of agriculture has become a priority. The main focus is on increasing the final yield and protecting the crops from unfavourable growing conditions in a sustainable way. A possible solution to this problem is represented by biostimulants, bioactive substances of diverse origins. A very large number of new biostimulants enter the market every year. However, a thorough knowledge of the mode of action of the substances in different crops and in different environmental conditions is still lacking. Traditional testing methods are time-consuming, expensive and, in most cases, destructive. Therefore, in the last years high-throughput automated phenotyping platforms started to be considered an interesting alternative to traditional characterization assays, drawing the attention of biostimulant producers. Different cameras and sensors can be implemented into high-throughput phenotyping platforms, allowing to screen the effects of different substances on a large number of morpho-physiological plant traits in a fast, efficient, cost-effective and non-destructive manner.
In our work, we developed a precise methodology to test the effects of a large set of protein hydrolysates on multiple plant species (wheat, Arabidopsis, lettuce and tomato) subjected to abiotic stresses (drought and salinity) at all phenological phases, from seed up to the crop maturity. A large number of morpho-physiological traits of the plants were analysed throughout their life cycle, before and after the application of the PHs substances.
The original set of PHs has been subjected to an initial in vitro screening on Arabidopsis plantlets; the substances were applied as seed priming in three different concentrations. The best-performing PHs in control and salt stress conditions have then been used for trials in planta, where they were applied as foliar spray. With the use of a Plant Biostimulant Characterization Index (PBC), we were able to categorize the substances into functional classes according to their mode of action, classifying them as Growth Promoters and /or Stress Alleviators. Leaves of the plants treated with the best- and worst-performing substances were collected and subjected to untargeted metabolomic analysis to elucidate the biochemical pathways activated by the PHs applications.
It was clear that the effects of the biostimulants on plants can vary depending on the mode and time of application, the growing conditions, the dose and the plant species they are applied to; therefore, before putting a new biostimulant on the market, it is essential to select the target crop species that could benefit from the treatment. High-throughput automated phenotyping platforms can be an extremely useful tool to speed up the testing process and precisely investigate the effects of the same substance on multiple morpho-physiological traits
