First report of the anti-cyanobacterial activity of the invasive weed Oxalis pes-caprae L. against Microcystis aeruginosa growth

This work aims to explore the anti-cyanobacterial potentialities of the weed Oxalis pes-caprae L. on Microcystis aeruginosa growth. In the current study, the aqueous extract of the aerial parts of Oxalis pes-caprae L. (AEOP) was tested to assess its activity on M. aeruginosa growth in an experimental bioassay. The anti-cyanobacterial effect of AEOP against M. aeruginosa was assessed in a batch culture experiment where several morphological and physiological indicators, and inhibition parameters were assessed. To reveal the potentially allelochemicals, phenolic compounds were analyzed in AEOP. Furthermore, the results from the bioassay demonstrated that AEOP inhibit the growth of M. aeruginosa in a concentration dependent way. Microcystis cell densities were significantly reduced during the bioassay period at the different tested concentrations (0.25, 0.5, 0.75, and 1 mg/ mL). Under both highest concentration of AEOP (0.75 and 1 mg/mL), the inhibitory rate (IR) reaches 63% and 74 only after 4 d of experimentation, respectively. The highest IR (86%) was achieved on 10 d at the highest concentration (1 mg/mL). Additionally, during the 12-d experimental period, all four-treatment groups (0.25–1 mg/mL) demonstrated a significant decrease in the content of chlorophyll-a and carotenoids compared to the control. Overall, the obtained results demonstrate the anti-cyanobacterial effect of AEOP to control Microcystis growth. Moreover, the invasive weed Oxalis pes-caprae L. might be proposed as a potential ecofriendly alternative algaecide to control Microcystis blooms in the eutrophic water bodies.