Effect of Two Biostimulants, Based on <i>Ascophyllum nodosum</i> Extracts, on Strawberry Performance under Mild Drought Stress

The world’s population continues to grow while available natural resources, such as arable land, water, and quality soil, are decreasing. Therefore, it is essential to implement environmentally friendly crop management strategies, which include the use of biostimulants. This study analysed the effects on strawberry plants of Actysei^{<span style="font-variant: small-caps;">TM</span>} and Phylgreen^®, two commercial biostimulants based on extracts of the seaweed <i>Ascophyllum nodosum</i>. The study was conducted under field capacity (regular irrigation) and at 50% field capacity (mild water stress conditions) for 12 weeks. Different growth parameters of the aerial parts of the plants were measured weekly, such as the number of leaves, length of the longest leaf, leaf area, and the number of flowers and fruits produced, as well as the chlorophyll content, determined with a single-photon avalanche diode (SPAD) detector. At the end of the experiment, the plant material was collected, and the roots and aerial parts were weighed separately to obtain the fresh and dry weight of the samples. Fruit quality was assessed by analysing morphological parameters (weight and size) and some biochemical variables (proline, total soluble sugars, and antioxidant compounds contents). Actysei^{<span style="font-variant: small-caps;">TM</span>} application generally enhanced plant growth in control plants and under mild water stress conditions, even though root weight was reduced. In contrast, no significant effect of Phylgreen^® on vegetative growth was observed, except for stimulating the root growth of plants watered at field capacity. Both biostimulants, Phylgreen^® to a greater extent, showed an impact on the plants already seven weeks after their initial application, stimulating flower and fruit production, especially at field capacity.