Evaluating an Ascophyllum nodosum extract as an organic biostimulant on tomato

In this study, we present a comprehensive approach using phenomics and RNA-seq analysis for dissecting plant responses to biostimulant treatments. Tomato plants (Solanum lycopersicum cv. Micro-Tom) were grown in the growth chamber, greenhouse, and under open field conditions. Foliar treatments with an Ascophyllum nodosum biostimulant extract (ANE) were carried out with two doses (1 l/ha and 2 l/ha) at three different phenological stages (BBCH51, BBCH61, and BBCH65) within the flowering phase. Phenomics profiling highlighted higher net photosynthesis and stomatal conductance in all the growing conditions that resulted in improved fruit yield traits in ANE-treated plants when compared to the untreated ones. RNA-seq analysis revealed the highest number of differentially expressed genes (DEGs) with the lower dose of ANE (1 l/ha). The impact of the first ANE application recorded at the beginning of the flowering stage on the leaf transcript was moderate, whereas the second and third applications resulted in a higher number of DEGs. The functional enrichment analysis of the overall set of DEGs, irrespective of the plant phenological stage and dose of product application, highlighted a significant contribution of pathways related to photosynthesis and response to the stimulus. This molecular result hints at the major role exerted by the product on the plant photosynthetic processes, and this is consistent with the morpho-physiological results. This is the first comprehensive dual-omics approach for profiling plant responses to biostimulant applications across three different growing conditions.