Morphological and reproductive studies on the green filamentous pest Rhizoclonium-like affecting Agarophyton chilensis commercial farms in southern Chile

• Published in: Aquatic botany 2020-10, Vol.167, p.103291, Article 103291
• Main Authors: Aroca, G.E., Ramírez, M.E., Robotham, H., Avila, M.
• Format: Article
• Language: English
• Subjects: Agarophyton chilensis; aquaculture; Green tides; pest; Rhizoclonium-like
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/j.aquabot.2020.103291

•Since 2015 commercial farms of Agarophyton chilensis (pelillo), cultivated in southern Chile, have shown pest massification of a green filament seaweed (green tides).•Filaments of Rhizoclonium- like algae have been cultivated in laboratory and showed a wide range tolerance to temperature, salinity, photoperiod and nitrate concentration.•Performance of the strategy of propagation of this species is by asexual spores, high growth rates and fragmentation of the thallus.•-Asexual reproduction in laboratory was triggered by salinities >20 PSU and nitrate concentration higher than 0.14 mmol/L. Cultivation of Agarophyton chilensis, common name “pelillo”, in Chile began 40 years ago. Technology adopted has been based on culture by vegetative propagation and culture from spores. Mass seaweed culture is associated with increased instances of pests and/or disease, as has been observed in the agricultural sector. The aim of this work is to study the pest alga Rhizoclonium sp, and its development under different controlled environmental conditions, given that this alga has affected “pelillo” production in southern Chile since 2015. Fresh thalli of the pest alga collected from culture centers located in Maullín river were described morphologically in order to confirm the identity of the species. Filaments were cultured under different temperature (10, 16 and 20 °C), photoperiod (8:16; 12:12 and 16:8 L:D), salinity (5; 10; 20; 27 and 30 psu) and nutrient (0.14 and 0.28 mmol/L nitrate) conditions to evaluate growth and reproduction. Nevertheless, given the taxonomic status situation of the polyphyletic genus Rhizoclonium, the pest is named Rhizoclonium-like. It formed lateral branches under culture conditions tested and showed a wide range of tolerance to temperature, salinity, photoperiod and nitrate concentration. Growth increases with temperature, reaching a daily growth rate of between 5.5 and 5.9%/day at 16 and 20 °C respectively. Rhizoclonium-like reproduction is described for the first time under culture conditions in Chile. Formation of reproductive structures occurs in the vegetative cells generating reproductive structures (zoosporangia) that mature under 16 °C, salinity >20 psu and nitrate concentration >0,14 mmol/L, observing release and germination of spores. After reproduction filaments do not decay and grow again.