Antagonistic Effects of Spirulina platensis Extracts against some Seed-Borne Pathogens of Faba bean

Abstract

This study investigated the antifungal effectiveness of Spirulina platensis extract against major soilborne pathogens causing damping-off and root-rot in faba bean (Vicia faba), specifically Fusarium oxysporum, F. solani, Rhizoctonia solani, and Macrophomina phaseolina. Laboratory experiments revealed that the extract inhibited fungal growth and spore germination in a concentration-dependent manner. The 40% extract was particularly effective, achieving significant inhibition of mycelial growth and lowering spore viability. Chemical analyses using UV–Visible spectrophotometry and chromatography confirmed the presence of biologically active  ompounds, including chlorophyll a, phycocyanin, β-carotene, and various phenolic acids all of which are recognized for their antifungal
and plant-stimulating properties. Greenhouse experiments supported the lab findings, showing that applying the extract through a combined method (seed soaking and soil drench) at 40% concentration significantly reduced disease incidence. This treatment also improved seed germination and seedling vigor compared to infected plants that received no treatment. Moreover, treated plants exhibited higher activity of key antioxidant enzymes peroxidase (POD), polyphenol oxidase (PPO), and catalase (CAT) suggesting that the extract helped trigger the plants natural defence mechanisms. Altogether, the findings highlight the dual function of Spirulina platensis extract, it acts as both a protective antifungal agent and a physiological enhancer under disease stress. While the greenhouse results were less dramatic than those observed in the lab, the consistent, dose-responsive effects across all settings demonstrate the extract’s promise as a bioactive tool. The study recommends further large-scale field trials in diverse environments to validate its role in integrated disease management.