A new Halophytophthora species, H. porrigovesica, from subtropical and tropical mangroves

Abstract

A new oomycete was found from intertidal fallen leaves of mangroves in Japan and Thailand and is described here as Halophytophthora porrigovesica. This species is characterized by having an epapillate, ovate zoosporangium with a lens-shaped dehiscence plug-like material at the apex, and by forming an expanding long cylindrical vesicle prior to zoospore release. A key to 14 species and 2 varieties of Halophytophthora including the new species is proposed. The subtropical (Iriomote Is., Japan) strains and tropical (Thailand) strains were different in physiological properties and especially in the asexual reproduction. The subtropical strains showed a lower optimal temperature and wider range of suitable temperature and salinity for zoosporangium formation, whereas the tropical strains showed a higher optimal temperature and narrower range of temperature and salinity. These differences are explained as adaptations of the strains to the environmental conditions of their respective habitats. From the subtropical mangroves, six strains of the new species have been isolated only from submerged leaves of Sonneratia alba, while several strains have been isolated from tropical mangroves from the leaves of three species of mangrove trees, S. alba, Bruguiera gymnorrhiza and A vicen- nia alba. This indicates a change of taxon selectivity (host specificity) with the geographical distribution.