In vitro allelopathic effects of compounds from Cerbera manghas L. on three Dinophyta species responsible for harmful common red tides.

Allelopathy is regarded as an economic and eco-friendly approach for the control of harmful algal blooms (HABs) because allelochemicals degrade easily and cause less pollution than traditional algicides. We first surveyed the inhibitory effect of the traditional medicinal plant Cerbera manghas L. on the notorious dinoflagellates Alexandrium tamarense, Scrippsiella trochoidea, and Karenia mikimotoi. Then, we identified and quantified the potential algicidal compounds by UPLC-MS and determined their activity. The aqueous extract inhibited algae with EC50-120 h at 0.986, 1.567 and 1.827 g L-1 for A. tamarense, S. trochoidea, and K. mikimotoi, respectively. Three potential allelochemicals were quantified in the stock solution: quinic acid (QA) (28.81 mg L-1), protocatechuic acid (PA) (53.91 mg L-1), and phloridzin (PD) (26.17 mg L-1). Our results illustrated that 1) QA did not have an inhibitory effect, 2) PA had medium toxicity to algae (EC50-120h: 0.22, 0.28, and 0.35 mM for A. tamarense, S. trochoidea, and K. mikimotoi), and 3) PD had low toxicity (EC50-120h > 0.66 mM). These findings suggested that PA might be the main allelopathic compound in the aqueous extract of the studied algae. In addition, PA could have a negative effect on the photosynthesis of S. trochoidea by impeding the reduction of quinone electrons and destroying electron transfer in PSII. In summary, this was the first study to quantify allelochemicals in C. manghas fruit. Moreover, C. manghas and protocatechuic have the potential to be algicides to control and mitigate the HABs caused by dinoflagellates.