Extract from spent oyster mushroom substrate: Composition, and regulatory and protective activity on germinating wheat seeds

This study examines the biochemical composition of an aqueous extract from the spent mushroom substrate of oyster mushroom (Pleurotus ostreatus strain HK-35) and investigates its regulatory and protective properties. The major organomineral components of the extract included approximately 2% dry matter, comprising over 1.5% organic matter and less than 0.5% ash. The extract had a mildly alkaline pH. Primary organic components included proteins, carbohydrates (predominantly reducing sugars), and humic substances, with potassium, calcium, and phosphorus being the most abundant elements. In germination assays, a 10% extract enhanced wheat seed germination, whereas a 100% extract inhibited it. The 10% extract also enhanced superoxide dismutase activity and the expression of the SOD-1 gene and suppressed peroxidase activity. This treatment had no effect on catalase activity or the transcript levels of the studied CAT and POD genes. In contrast, the 100% extract suppressed peroxidase activity and gene expression; however, it had no effect on superoxide dismutase or catalase activity or their related gene transcripts. In antifungal assays, the 10% extract significantly inhibited the growth of phytopathogens in vitro. The mycelial mass of Aspergillus niger was reduced by more than 6-fold and its colony radius by almost 8-fold, while for Alternaria alternata, mass was reduced by more than 7-fold and colony radius by approximately 15-fold, compared to the control.