An in-vitro study of Himalayan plant extracts against oomycetes disease Saprolegniasis in rainbow trout (Oncorhynchus mykiss)

Aim: This study aimed to investigate the effectiveness of ethanolic extract of three Himalayan plants Myrica esculenta, Thymus linearis and Butea monosperma on hyphal germination, colonisation and sporulation of two species of Saprolegnia (Saprolegnia parasitica and S. australis) isolated from rainbow trout, Oncorhynchus mykiss. Molecular docking of active ingredients of M. esculenta, Myricetin with effector proteins of S. parasitica was also performed to investigate the target binding sites for drug development. Methodology: Minimum inhibitory concentration (MIC), mycelium growth inhibition, spore germination, and inhibition was performed with the most effective concentrations. Molecular docking was carried out with AutoDock Vina software to investigate target binding sites with S. parasitica. Results: Extracts from Myrica esculenta, Thymus linearis and Butea monosperma showed MIC values of the 25, 100, 50 mg ml-1 against S. parasitica and 25, 50, 25 mg ml-1 against S. australis hyphal growth, respectively. Nevertheless, malachite green as reference control was effective with a MIC value of 2.5 mg l-1. The concentration required to inhibit S. parasitica and S. australis spores were (50) Myrica esculenta, (25) Thymus linearis, (100) Butea monosperma in mg ml-1 and (50) Myrica esculenta, (50) Thymus linearis, (100) Butea monosperma in mg ml-1, respectively. Interpretation: The study concludes that M. esculenta and B. monosperma are effective against Saprolegniasis and could be used as phyto additives.