The Influence of Biological Measures on Strawberry Plant Growth, Yield, and Fruit Quality

Finding safe and efficient plant protection measures is one of the major challenges in horticulture. This study evaluated the biological effects of the Thymus vulgaris essential oil and of Bacillus halotolerans and B. velezensis bacterial mixture on strawberry growth and fruit quality properties, as well as on Botrytis cinerea severity. The experiment was conducted in a high-tunnel greenhouse with the strawberry cv. Sonsation. Treatments: (1) Control-untreated; (2) Bacteria-with Bacillus halotolerans and B. velezensis, four times during flowering; (3) Thyme I-T. vulgaris essential oil (EO), four times during flowering; (4) Thyme II-T. vulgaris EO, four applications supplemented by three additional applications during fruit ripening; (5) Biofungicide I-Bacillus subtilis QST 713, four times supplemented by three applications; (6) Biofungicide II-Clonostachys rosea J1446, four times during flowering. In the first year (2023), the highest total yield was observed in Thyme II, and in the second year (2024), the highest total yield was observed in Thyme I. The results did not reveal any visual phytotoxic effect on plant leaves. The average fruit diameter increased from 28 mm up to 31 mm in 2023 and from 35 mm to 39 mm in 2024. The average soluble solids content increased from 9.4 to 11.4 °Brix in 2023 and from 7.2 to 7.7 °Brix in 2024. The highest ascorbic acid content in 2023 was observed in Biofungicide II and Biofungicide I treatments, respectively, 79.9 mg % and 75.4 mg %. Similarly, in 2024, the highest ascorbic acid content was observed in Bacteria, Biofungicide I, and Biofungicide II treatments-39.3-40.2 mg %. In vitro, the lowest B. cinerea severity on strawberry leaves in 2023 was recorded in Thyme I and Thyme II treatments (~6-7%), while in 2024, the severity in these treatments was higher -20-22%. Thyme treatment showed a stable reduction in B. cinerea on leaves in vitro over both years.