Inoculación de semillas de cebolla con microorganismos benéficos: Efectos sobre el control biológico de enfermedades y sobre el crecimiento de las plántulas

In Uruguay, onion production is of great economic importance; however, there are still fewer research-based tools available for integrated disease management compared to those developed for protected horticultural crops. The country’s soils are characterized by high fertility and a broad diversity of microorganisms. Nevertheless, the intensive use of horticultural production systems leads to their progressive degradation, turning them into environments favorable for the development of various pathogens. National production is mainly based on cultivars developed by INIA and the Facultad de Agronomía, and most of the commercialized seed is nationally produced and certified. In this context, offering seed inoculated with beneficial microorganisms would allow the replacement of chemical seed treatments, taking advantage of biological mechanisms to contribute to a more sustainable integrated management approach.

Seed inoculation with beneficial microorganisms represents a tool with the potential to optimize resource use and promote improved early plant growth; however, its application in horticulture remains uncommon. In this study, the effect of onion seed inoculation with Trichoderma afroharzianum strain TR48 and Clonostachys rhizophaga strain P43, applied separately, was evaluated. The cultivars Vicky F1 (Italy) and Pantanoso del Sauce CRS (Uruguay) were used. The microorganisms were grown on PDA medium plates, from which spores were harvested and subsequently encapsulated with additives to enhance their viability. Viability was assessed with and without additives at 0, 7, and 14 days after inoculation under two storage conditions: room temperature and refrigeration at 4–5 °C.

In dual culture assays, Clonostachys P43 showed a significant effect in controlling Botrytis (43.3 cm² of pathogen area in the presence of P43 compared to 55.9 cm² in the control), although it did not show an effect against Fusarium. In contrast, Trichoderma TR48 exhibited greater control capacity against both pathogens (20.9 and 25.1 cm² of Botrytis and Fusarium area, respectively, compared to 55.9 and 35.9 cm² in the controls), which was associated with its higher in vitro growth rate. In a bioassay conducted in sand artificially infested with Fusarium, both strains had a positive effect on seedling weight when using the low-virulence strain UR01; however, they were not effective against the more virulent strain NL93816 under the methodology applied. The average seedling weight in the presence of NL93816 was 0.030 g, whereas with inoculation it reached approximately 0.076 g per seedling.

Both strains maintained their viability on PDA up to 7 days after inoculation (17 cm² for TR48 and 11 cm² for P43), decreasing at 14 days (12.5 cm² and 8 cm², respectively) in the Vicky cultivar; a similar pattern was observed in Pantanoso and under both storage temperatures. The use of additives resulted in high levels of in vitro contamination, indicating the need for methodological adjustments. Under field conditions, at 60 and 90 days after sowing, inoculated seeds produced plants with greater weight and leaf area, although with smaller stem diameter. Natural disease incidence was low and no significant differences were detected. The use of beneficial microorganisms represents a promising alternative to strengthen crop health and sustainability.