Metabolic Study of Cucumber Seeds and Seedlings in the Light of the New, Controversial Trend of Preventive Use of Systemic Fungicides

**Background:** Cucumber is the third most commonly produced fruit vegetable crop globally, with over 91 million metric tons produced in 2020. Fungal infections, particularly powdery mildew (Podosphaera fusca) and downy mildew (Pseudoperonospora cubensis), cause significant economic losses. While fungicides are primarily used to control these pathogens, some reports suggest certain fungicide classes (strobilurins, triazoles) may have positive physiological effects on plants, including increased photosynthetic pigments, improved hormonal balance, and enhanced stress tolerance. This has led to a controversial new trend of using systemic fungicides as preventive growth promoters in healthy plants. However, commercially available fungicide formulations contain mixtures of active substances, and their combined effects on plant metabolism remain poorly understood. This study aimed to investigate the metabolic effects of two commercial systemic fungicides—Scorpion 325 SC (azoxystrobin + difenoconazole) and Magnicur Finito 687,5 SC (propamocarb hydrochloride + fluopicolide)—on cucumber seed germination and seedling physiology.

**Methods:** Cucumber seeds (Cucumis sativus variety Izyd F1) were surface-sterilized and subjected to two experimental variants. In Variant 1 (presowing seed treatment), 1.0 ± 0.1 g of seeds were soaked in 5 mL of distilled water or fungicide solution (0.1% Scorpion 325 SC or 0.3% Magnicur Finito 687,5 SC) for 4 hours in darkness, then germinated on moist filter paper in Petri dishes under controlled phytotron conditions (16h/8h light/dark, 25°C/20°C, 70% humidity) for 7 days. In Variant 2 (foliar application), 8-day-old cucumber seedlings were sprayed with 1 mL of fungicide solution and harvested over 5 days post-treatment. Measurements included germination rate, phytase activity (via Pi release from sodium phytate), phytic acid content (by ferric precipitation method), inorganic phosphate (Pi) content (malachite green method), adenylate content (ATP, ADP, AMP by HPLC), adenylate energy charge (AEC), 31P NMR phosphorus profiles, photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), total phenolic content (Folin-Ciocalteu method), total antioxidant content (ABTS assay), and antioxidant capacity (DPPH radical-scavenging activity). Statistical analysis used one-way ANOVA with Tukey's test (p ≤ 0.05).

**Key Results:** For presowing treatment, the highest germination rate at 2 DAT was for Magnicur Finito (52.4%) and lowest for Scorpion (39.4%). At 3 DAT, control germination was 86.9 ± 4.7% versus Scorpion at 70.9 ± 7.4% (not statistically significant). Acid phytase activity reached maximum at 7 DAT for Scorpion (285.51 ± 18.88 mU g⁻¹ DW) and Magnicur Finito (184.94 ± 19.20 mU g⁻¹ DW), while control decreased after 4 DAT to 102.19 ± 4.17 mU g⁻¹ DW. Phytic acid decreased by approximately 17% for control, 14% for Scorpion, and 26% for Magnicur Finito at 7 DAT versus 0 DAT. ATP content ranged from 40.18–103.02 µg g⁻¹ DW for control, with Scorpion showing fluctuating ATP and AMP levels. AEC ratios ranged from 0.46–0.58, indicating predominance of anabolic processes. 31P NMR showed phosphate monoesters comprised 49.7–75.3% of phosphorus species, with orthophosphates at 24.5–49.8%. For foliar application, total chlorophyll ranged from 7.36–10.69 mg g⁻¹ DW, with maximum at 2 DAT for all treatments. Chlorophyll b remained stable (2.00–2.70 mg g⁻¹ DW). Total phenols ranged from 5.89–8.17 mg GAE g⁻¹ DW, and total antioxidants from 2.15–3.10 mg Trolox g⁻¹ DW. Antioxidant activity (RSA) ranged from 4.45–13.79%, with Scorpion showing the highest at 4 DAT (13.12 ± 0.37%). AEC ratios in aboveground parts ranged from 0.39–0.53, indicating catabolic process predominance, with significant differences between control and both fungicide treatments. In roots, AEC ranged from 0.40–0.49 with no significant differences from control. 31P NMR of aboveground parts showed orthophosphates as the dominant fraction (76.3–88.5%).

**Clinical Implications:** This study provides important evidence that the metabolic effects of systemic fungicides on plants are complex and not uniformly beneficial, challenging the emerging practice of using these compounds as preventive growth promoters in healthy crops. The observed disruptions in phytase activity, energy status (AEC), and antioxidant systems indicate that fungicide application induces stress responses in plants rather than simple physiological enhancement. The finding that Scorpion 325 SC slowed germination and limited stem growth suggests potential negative impacts on early plant development. Notably, while no negative effects on root metabolism were observed (based on AEC ratios), the aboveground metabolic disruptions raise concerns about overall plant health and resilience. The study also highlights that commercial fungicide formulations, containing multiple active ingredients, may produce different effects than individual compounds studied in isolation. These findings have implications for agricultural practices, suggesting that the preventive use of systemic fungicides requires careful consideration of metabolic consequences beyond pathogen control. The authors conclude it is "too early to unequivocally state the benefits of using systemic fungicides as preventive agents" and raise additional concerns about impacts on beneficial soil microorganisms (arbuscular mycorrhizal fungi) and the potential for increased pathogen resistance with excessive use.