Valorization of Agroindustrial Residues between Annatto (Bixa orellana L.) and Oyster Mushroom (Pleurotus ostreatus var. Florida) Cultivation: a Cascade Approach

• Mushroom residue boosts annatto seedling germination and growth up to 60% inclusion.

• Annatto residue supports Pleurotus yields with substitutions up to 80%.

• Pleurotus strain 16/01 shows superior mushroom productivity and efficiency.

• Mushroom and annatto residue use cuts costs and supports regional small producers.

Annatto production generates agroindustrial residues (AAR) with no defined use. Meanwhile, mushroom cultivation repurposes another by–product, spent mushroom substrate (SMS). Integrating both into a cascade approach offers a sustainable solution that adds value and supports local small–scale farmers. This study aimed to assess the use of SMS for growing annatto seedlings and AAR as a substrate for Pleurotus ostreatus var. Florida. In the first experiment, the standard annatto substrate was replaced by SMS at 20– 80%. Germination and biometric characteristics were evaluated of seedlings. Adding up to 60% SMS improved germination without significantly affecting seedling quality, making it a viable option for nurseries. The second experiment replaced rice straw with AAR (0%, 20%, 40%, 60%, 80%, 100%) for two strains of P. ostreatus (16/01 and 20/01). Although AAR reduced mushroom yield by up to 16%, it did not affect the productive aspects or earliness of fruiting. Using up to 60% AAR could reduce costs related to rice straw acquisition and transportation. Strain 16/06 showed higher productivity than 20/01. In conclusion, integrating annatto and P. ostreatus production in a cascade approach is sustainable and adds value to AAR and SMS waste.