Microbial Biostimulants and Their Combinations Alter Phytochemical Quality of Strawberry Fruits in a Soilless Cultivation System

This study investigated the effect of arbuscular mycorrhizal fungi (AMF), Trichoderma harzianum, and their combinations on yield and quality of strawberry fruits in a soilless cultivation system. Six treatments were applied, control (no biostimulants), T. harzianum (TH), Claroideoglomus etunicatum (CE), a multispecies mycorrhizal community (IP CS), TH + CE, and TH + IP CS, arranged in a randomized block design with four replicates. While total fruit yield was not significantly affected, the application of T. harzianum, either alone or in combination with AMF, enhanced cumulative fruit production. The use of C. etunicatum improved sugar content and the sugar/acid ratio by 28% and 31%, respectively, compared to the control. Biostimulant treatments also increased total phytochemical content, particularly with the multispecies inoculant IP CS (increased anthocyanin content by 39% compared to the control) and the combinations TH + CE (flavonoid content 41% higher than the control) and TH + IP CS (flavonoid content 39% higher than the control). Multivariate analysis grouped the treatments into two groups, with the control (no biostimulants) forming a distinct group. In conclusion, biostimulation of ‘San Andreas’ strawberry plants improved fruit quality without significantly increasing yield. The combined use of AMF and T. harzianum is proposed as a sustainable strategy for enhancing fruit quality in soilless strawberry cultivation systems.