Innovative Use of <i>Hermetia illucens</i> Frass Extract as Priming to Promote Tomato and Wheat Growth and Protection

ABSTRACT Frass deriving from Hermetia illucens was explored as a new sustainable tool to induce biostimulation and/or antifungal activity in Solanum lycopersicum L. var Cerasiforme and Triticum durum Desf. var Simeto against the soil‐borne pathogens Fusarium spp. Phytotoxicity and in vitro antagonism assessments (mycelial growth inhibition of about 40%) allowed to define the optimal dilution of 10% of pasteurised‐frass extract (pFE) to employ for seed priming. Germination tests on water agar demonstrated the priming effectiveness for wheat, but not for tomato, as the analysed parameters were not positively affected. The pFE was used also in combination with the known biocontrol agent Trichoderma harzianum T22 (T22), demonstrating that they could work together to obtain a good growth promotion and protective effect in wheat. Indeed, the priming with pFE significantly reduced the disease incidence of almost 60% or 80%, compared to the infected control, if used alone or combined with T22, respectively. The ability of frass extract to control F. sporotrichioides in wheat was attributed to both enzymatic and non‐enzymatic responses, due to observed differences in total phenolic content (TPC) and superoxide dismutase activity (SOD) in seedlings derived from treated seeds, compared to untreated control. Our findings highlight the great potential of H. illucens frass as a sustainable, green, and circular economy‐based tool in agricultural systems.