This study shows that T34 Biocontrol® reduces Verticillium dahliae microsclerotia by 70-80% without altering soil biodiversity, while mineral fertilization doubles the inoculum in the absence of the biocontrol.
Verticillium wilt is one of the most devastating diseases of Mediterranean olive orchards. Its causal agent, Verticillium dahliae, can persist for years thanks to the formation of microsclerotia: resistance structures that remain viable even in the absence of cultivation. Control of this inoculum is one of the great challenges in olive health management, especially in intensive systems where nitrogen fertilization practices can aggravate the disease.
A new study published in Frontiers in Microbiology (Segarra, Sancho-Adamson, Trillas & Romanyà, 2025) provides key scientific evidence on two management factors: mineral fertilization and the application of Trichoderma asperellum strain T34.
The work analyzes how both influence pathogen inoculum and soil microbiota of young olive trees.
Summary of the study
The researchers set up a greenhouse trial with Picual olive trees for 20 months. The factorial design evaluated three factors:
Mineral fertilization
(yes/no)
Inoculation with V. dahliae (yes/no)
T. asperellum T34 application (yes/no)
They were measured:
- Microsclerotia of V. dahliae in the soil
- Bacterial and fungal microbiota composition (16S and ITS).
- Alpha diversity (richness and Shannon index)
Key results
The study demonstrates that the application of T. asperellum T34 very significantly reduces the concentration of microsclerotia in the soil, regardless of the fertilization regime.
En condiciones sin aporte de fertilizantes, el tratamiento con T34 consigue una reducción del 82%, mientras que en suelos fertilizados la disminución alcanza igualmente un 72%. Estos resultados evidencian que la eficacia del producto no depende de la fertilización, confirmando que T34 actúa de forma consistente incluso cuando se aplica en escenarios agronómicos distintos, aportando un control fiable de la enfermedad en múltiples condiciones de manejo del cultivo.
Mineral fertilization doubles the inoculum of the pathogen
NPK application increased microsclerotia twofold compared to unfertilized soils.
Sequencing analysis further showed:
Significant increase in readings
of V. dahliae
Changes in soil structure
(fungi and bacteria)
This result coincides with previous studies: an excess of nitrogen can favor both the germination of microsclerotia and the development of the pathogen.
T34 does not alter soil microbial biodiversity.
Diversity indices (Richness and Shannon) showed no significant changes between T34-treated and untreated soils.
This means that:
T34 does not displace natural microbial populations or cause undesirable effects on soil functionality, a key criterion for environmental safety in microorganisms for phytosanitary use.
Fertilization, not Trichoderma, is the factor that most modifies microbial communities.
Los análisis de PERMANOVA y PCoA ponen de manifiesto patrones claros en la dinámica microbiana del suelo. La fertilización emerge como el factor con mayor impacto, generando cambios significativos y profundos tanto en las comunidades bacterianas como fúngicas. En contraste, la aplicación de T34 no produce modificaciones detectables en la estructura microbiana, lo que confirma su compatibilidad con la microbiota del suelo. Por su parte, la presencia de V. dahliae muestra un efecto más limitado, cuya magnitud depende en gran medida de si el suelo ha sido fertilizado o no. Estos resultados evidencian que las prácticas de manejo agronómico influyen más en la composición microbiana que el propio biocontrolador.
What do these results imply for Verticillium management?
Inoculum reduction is possible using biological tools: The significant decrease in microsclerotia suggests that T. asperellum T34 contributes to reducing the soil inoculum pool, a key objective in integrated management strategies.
Nitrogen management is critical: Understanding the role of fertilization is essential:
- N excesses favor V. dahliae.
- Fertilization can alter the microbiota and reduce the system’s natural resistance.
- Integrating sound fertilization practices helps to reduce pathogen pressure
The use of biocontrol should be considered within combined strategies: Although the trial showed no visible symptoms on the plant – probably due to high summer temperatures or a suppressive effect of the soil – the reduction of inoculum lays a solid foundation for integrated Verticillium management programs in olive.
Value for producers, consultants and distributors
For the agricultural sector, this study provides several fundamental certainties:
– T34 acts against inoculum without affecting soil microbial health, a critical aspect in sustainable agriculture.
– Fertilization must be precisely managed, especially in areas with a history of Verticillium.
– Biocontrol and agricultural practices can be combined, but require an integrated assessment.
– Biocontrol microorganisms can have a direct impact on resistance structures, one of the major management difficulties in soil diseases.
"This study reinforces the importance of developing solutions based on soil-safe and effective microorganisms within integrated management strategies. Reducing Verticillium inoculum without altering biodiversity is a relevant advance for both science and agricultural practice."
Segarra, G., Sancho-Adamson, M., Trillas, M.I., & Romanyà, J. (2025). Impact of mineral fertilization and Trichoderma application on soil microbiota of young olive trees inoculated with Verticillium dahliae. Frontiers in Microbiology, 16:1708981.
