Oomycete and chytrid infections of the marine diatom Pseudo-nitzschia pungens (Bacillariophyceae) from Prince Edward Island, Canada

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Abstract:

Two eukaryotic parasites were found infecting the bloom-forming marine diatom Pseudo-nitzschia pungens (Grunow ex Cleve) Hasle in Prince Edward Island, Canada. The most common was an oomycete; the other, seen once, was a chytrid. The structure of the discharged sporangium of both is remarkably similar. The oomycete parasite caused the host cell to lay down several extra girdle bands as the parasite thallus grew and swelled to form a holocarpic, endobiotic, nonwalled multinucleate thallus within the host cytoplasm. At maturity the thallus formed a single discharge tube with a thickened base and a thin papillate apex. Many biflagaellate zoospores were formed that burst out from the discharge tube. Ultrastructural characteristics of the oomycete thallus include mitochondria with tubular cristae and vesicles with dense body inclusions, features common to the oomycetes. The morphological characteristics and biflagellate condition indicate a placement of this form in the genus Ectrogella. However, neither flagellar mastigonemes nor flagella flimmer vesicles were found. The absence of flimmers may indicate a closer phylogenetic relationship to Haptoglossa, an endoparasitic oomycete of nematodes, the zoospores of which lack flagellar mastigonemes. Cell infection frequencies ranged from 0.6%–15.9% during 1992–1995, at the four sampling sites.

L'auteur a trouvé deux parasites eucaryotes infectant le Pseudo-nitzschia pungens (Grunow ex Cleve) Hasle une diatomée marine formant des prolifération d’algues à l'Île du Prince Édouard, au Canada. Le plus commun est un oomycète; l'autre, observé une seule fois appartient aux chytrides. Les structures de décharge des sporanges des deux espèces sont remarquablement similaires. Le parasite oomycète emmène la cellule hôte à former plusieurs ceintures supplémentaires, à mesure que le thalle du parasite se développe et se gonfle pour former un thalle holocarpe, endobiote, multinucléé non septé dans le cytoplasme de l'hôte. À maturité, le thalle forme un seul tube de décharge possédant une base épaissie et un apex mince papillé. Il s'y forme plusieurs zoospores biflagellées qui s'échappent par le tube de décharge. Les ultrastructures du thalle de l'oomycète comportent des mitochondries avec crêtes tubulaires et des vésicules contenant des corps denses, autant de caractéristiques propres aux oomycètes. Les caractères morphologiques et la condition biflagellée indiquent l'appartenance de cette forme au genre Ectrogella. Cependant, l'auteur n'a jamais observé la présence de mastigonèmes flagellaires ou de flagelles munis de vésicules ciliées. L'absence de cils pourrait indiquer une relation phylogénétique plus étroite avec l'Haptoglossa, un oomycète parasite des nématodes, dont les zoospores ne possèdent pas de mastigonèmes flagellaires. On a observé une fréquence d'infection cellulaire de 0.6–15.9% de 1992 à 1995, sur les quatre sites échantillonnés.

Document Type: Research Article

Publication date: November 1, 2009

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  • Published since 1929, this monthly journal features comprehensive research articles and notes in all segments of plant sciences, including cell and molecular biology, ecology, mycology and plant-microbe interactions, phycology, physiology and biochemistry, structure and development, genetics, systematics, and phytogeography. It also publishes commentary and review articles on topics of current interest, contributed by internationally recognized scientists.

    Previously published as the Canadian Journal of Botany
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