Infestation by Colaconema daviesii (Rhodophyta, Colaconematales) of haploid and diploid thalli of edible red seaweed Chondracanthus chamissoi (Rhodophyta, Gigartinales): effects on growth and survival

Colaconema daviesii, a filamentous red alga, has been previously reported as an endophyte infesting Chondracanthus chamissoi. This study focuses on identifying the symptoms of C. daviesii infesting on haploid and diploid thalli of C. chamissoi. Co-cultivation of C. daviesii with diploid and haploid thalli of C. chamissoi was conducted under two treatments. Treatment 1 was under a 12:12 h (L:D) photoperiod for 40 days. Treatment 2 was under a 12:12 h (L:D) photoperiod for 20 days, followed by a 16:08 h (L:D) photoperiod for an additional 20 days. Parameters such as the density and coverage of C. daviesii filaments on C. chamissoi thalli were measured, as well as the growth rate and survival of C. chamissoi. Infestation occurred in both treatments and phases, with an increase in the presence of C. daviesii as the photoperiod extended. This relationship negatively affected the host in all measured parameters, with the diploid phase being more adversely affected. Infestation begins with spores under a 12:12 h (L:D) photoperiod condition, and filament development is observed on C. chamissoi thalli as the photoperiod increases. Early infestation symptoms were not evident, complicating the recognition of C. daviesii on haploid and diploid thalli of C chamissoi. The potential risk of transferring C. chamissoi contained filaments of C. daviesii through cultivation is postulated.