Dual role of Eisenia fetida and its excreta in boosting tomato biomass and defense against Botrytis cinerea

Soil organisms are key to plant growth and ecosystem functions. Earthworms (EWs) enhance soil and indirectly affect plant growth, while their cutaneous excreta (CEx) contain bioactive compounds capable of eliciting plant responses. However, their role in plant immunity is still not well understood. We hypothesized that EWs and their CEx enhance plant defense against foliar pathogens by activating induced resistance. To test this, we evaluated the effect of Eisenia fetida and their CEx on Solanum lycopersicum (tomato), focusing on growth, physiology, and defense response against Botrytis cinerea. Plants were exposed to EWs, CEx, or water (control), followed by B. cinerea infection after two weeks. Gene expression of defense markers was assessed at 24 and 48 h post-inoculation (hpi), while physiological parameters and disease severity were evaluated at 72 hpi. EWs increased shoot biomass compared to CEx, while both treatments reduced root dry weight, suggesting a possible shift in resource allocation. CEx significantly reduced B. cinerea-induced leaf damage and showed a trend for flavonoid accumulation, a known marker of induced resistance. Both treatments, EWs and CEx, activated the jasmonic acid (JA) signaling pathway, with CEx specifically upregulated genes involved in fungal pathogen defense, sustaining their expression over time. The present study offers, for the first time, clear evidence that earthworm-derived CEx can induce resistance by stimulating plant defense responses. Further biochemical, transcriptomic, and metabolomic analyses are needed to confirm indirect results, along with field validation. Nonetheless, the findings underscore the crucial role of soil biodiversity in enhancing crop resilience.