A pathogen of New Zealand Pyropia plicata (Bangiales, Rhodophyta), Pythium porphyrae (Oomycota)

© 2017 The Korean Society of Phycology. Geographic distributions of pathogens are affected by dynamic processes involving host susceptibility, availability and abundance. An oomycete, Pythium porphyrae, is the causative agent of red rot disease, which plagues Pyropia farms in Korea and Japan almost every year and causes serious economic damage. We isolated an oomycete pathogen infecting Pyropia plicata from a natural population in Wellington, New Zealand. The pathogen was identified as Pythium porphyrae using cytochrome oxidase subunit 1 and internal transcribed spacer of the rDNA cistron molecular markers. Susceptibility test showed that this Pythium from New Zealand was able to infect several different species and genera of Bangiales including Pyropia but is not able to infect their sporophytic (conchocelis) phases. The sequences of the isolated New Zealand strain were also identical to Pythium chondricola from Korea and the type strain from the Netherlands. Genetic species delimitation analyses found no support for separating P. porphyrae from P. chondricola, nor do we find morphological characters to distinguish them. We propose that Pythium chondricola be placed in synonymy with P. porphyrae. It appears that the pathogen of Pyropia, both in aquaculture in the northern hemisphere and in natural populations in the southern hemisphere is one species

Stress metabolite pattern in the eulittoral red alga Pyropia plicata (Bangiales) in New Zealand – mycosporine-like amino acids and heterosides

© 2018 Intertidal rocky shore ecosystems are affected by steep environmental gradients such as fluctuating solar irradiation and salinity along the marine-terrestrial interface. The eulittoral red alga Pyropia plicata (Bangiales) is endemic and abundant to coastal regions of New Zealand and almost unstudied in terms of ecophysiological performance under radiation and salinity stress. Therefore, the acclimation potential of this species against enhanced ultraviolet radiation (UVR) and osmotic stress was evaluated in a combination of field and laboratory experiments with an emphasis on stress metabolite concentrations (UV-sunscreens, organic osmolytes). Samples of P. plicata were collected at the same site in the intertidal zone of Wellington, New Zealand over three seasons (April–November 2016) and used in independent UV and salt stress experiments under controlled conditions. The mycosporine-like amino acids (MAA) shinorine and porphyra-334 were the quantitatively dominant UV-sunscreen compounds, and the total concentrations varied over the year between 5 and 14 mg g−1 dry weight (DW), but neither UVR nor PAR had a significant impact on the total or individual MAA concentrations. A UV radiation stress experiment was conducted, but the total MAA concentrations of 6–8 mg g−1 DW did not change, neither did the contents of shinorine (~ 3 mg g−1 DW) nor that of porphyra-334 (4–5 mg g−1 DW). This suggests, that P. plicata has sufficiently high UV-sunscreen amounts and hence does not respond to changes in UV radiation. Pyropia plicata contained three heterosides (floridoside, D- and L-isofloridoside), which act as organic osmolytes. Seasonally the total concentrations of these compounds varied between 203 and 1226 mmol kg−1 DW, with L-isofloridoside quantitatively dominating all samples. A salt stress experiment showed an increase in the total heteroside concentrations in P. plicata with increasing salinities. However, floridoside was the most up-regulated heteroside under hypersaline conditions indicating its key role in osmotic acclimation. Our data indicate that P. plicata always contains various stress metabolites in consistently high concentrations which mitigate against environmental changes typical of the intertidal zone of New Zealand