The phaeophyte Hizikia fusiformis extracts suppress rhizoid and blade formation in seaweeds

<p class="MediumGrid2"><strong>Background</strong>: Plants, including marine algae, produce allelochemicals that influence the growth, survival, and reproduction of other organisms.</p><p class="MediumGrid2"><strong>Questions</strong>: To identify natural algicidal or antifouling allelochemicals, we screened 18 common seaweed extracts for suppression of rhizoid and blade production in a convenient <em>Porphyra suborbiculata</em> monospore assay.</p><p class="MediumGrid2"><strong>Species study and data description</strong>: Addition of extract from the most potent phaeophyte, <em>Hizikia fusiformis</em>, suppressed rhizoid formation, rhizoid number, rhizoid length, blade formation, and blade length.</p><p class="MediumGrid2"><strong>Study site and dates</strong>: Seaweed thalli for methanol extraction were collected on the coast of Korea from October 2012 to July 2015.</p><p class="MediumGrid2"><strong>Methods</strong>: Extracts were tested using the <em>P. suborbiculata</em> monospore assay system.</p><p class="MediumGrid2"><strong>Results</strong>: The 50 % suppression doses were 15 <em>µ</em>g ml^-1 for rhizoid formation, 2.4 <em>µ</em>g ml^-1 for rhizoid number, 13 <em>µ</em>g ml^-1 for rhizoid length, 6 <em>µ</em>g ml^-1 for blade formation, and 11 <em>µ</em>g ml^-1 for blade length. The <em>H. fusiformis</em> extract also suppressed rhizoid and blade production in leafy green (<em>Ulva pertusa</em>) and brown (<em>Undaria pinnatifida</em> and <em>Ecklonia cava</em>) seaweed spores, as well as suppressing diatom settlement.</p><p><strong>Conclusions</strong>: The allelochemicals that suppressed or eliminated competing seaweed species may be efficacious for new seaweed control technologies, including the development of antifouling or algicidal agents based on natural products.</p>