Controlled incubation, leachate, and pot assays of shrimp shell‐based compost for suppressing Verticillium dahliae in olive

BACKGROUND Verticillium wilt of olive ( Olea europaea L.), caused by Verticillium dahliae Kleb., is difficult to manage because long‐lived microsclerotia persist in soil, and disease risk is influenced by inoculum distribution, irrigation and cultivar susceptibility. This study evaluated mature shrimp shell‐based compost (SSC), a chitin‐containing circular‐economy amendment, for suppressing V. dahliae in naturally infested olive‐orchard soil, inhibiting fungal growth in vitro , and reducing disease in a controlled pot assay. Green‐waste compost (GWC) was included as a reference amendment. RESULTS After 60 days, SSC 5% reduced microsclerotia density by 39.6% and viable microsclerotia by 42.8% relative to unamended soil. Nonsterile SSC leachate inhibited radial growth by 83.7% at 50% (v/v), whereas filter‐sterilized leachate retained 58.3% inhibition. In the controlled pot assay, SSC 5% lowered model‐estimated final disease incidence from 85% to 30%, and reduced disease severity by 46.5% relative to the infected control. SSC 5% also increased plant height, shoot and root dry weight, leaf area, SPAD index, and rhizosphere chitinase and beta‐glucosidase activities. CONCLUSION SSC suppressed V. dahliae survival and improved olive plant performance under controlled incubation, in vitro and pot conditions. The results identify SSC as a candidate amendment for further testing, but the proposed inhibitory, chitinolytic, microbiome‐mediated, and plant‐vigor mechanisms remain hypotheses pending microbiome, pathogen‐DNA, metabolite, plant‐defense and field validation studies.