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

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.

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.

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. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.