Sorgoleone, a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

Abstract

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20μgmL−1. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25μgmL−1. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5μgmL−1 and 99% of Anabaena affinis Lemmermann at 4μgmL−1. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16μgmL−1 sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1μgmL−1 during the test period. The no observed effect concentration (NOEC) value was 1.5μgmL−1 for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.