4th International Workshop on Oomycetes:
Phytophthora, Pythium and Phytopythium
Introduction
Objectives of the Workshop
This workshop aims to provide hands-on training on morphological and molecular tools used to identify species within the genera of Phytophthora, Pythium and the newly erected Phytopythiums. Participants will have the chance to examine a selected assemblage of species from each genus using type isolates. We will have also most of the type isolates present to view for the experienced participants. Instructors will demonstrate how to isolate from different environments such as plant material or soil, maintain cultures, and conduct morphological & molecular analysis using the most advanced tools. A day of presentation at the end of the meeting will give participants the time to discuss concepts, population biology, description of new taxa and disease problems caused by the three genera around the world.
The Oomycetes
Oomycetes have many fungus-like characteristics, but lack taxonomic affinity with true fungi. Instead oomycetes are phylogenetically relatives of diatoms and brown algae within the Kingdom Straminipila. Members of the genera Phytophthora and Pythium cause destructive diseases of thousands of plant species including commercially important hosts. Identification to species levels in both genera is important due to their significance as plant pathogens and the acquisition of resistance to fungicides observed in certain species.
PHYTOPHTHORA
The importance of the genus Phytophthora both to human history and to the origin of the science of plant pathology has been recognized since the 1840's at the time when the unexpected "potato disease" affected crops in Europe and the USA culminating in the famous "Irish Potato Famine." To the present 106 species have been described since De Bary in 1876 coined the name Phytophthora("plant destroyer"). Over the years Phytophthora has turned out to be the most studied genus of plant pathogens. New emerging species within this genus with great environmental damage makes this group of plant pathogens a high priority in regulatory actions.
PYTHIUM
The genus Pythium is ecologically and physiologically an exceptional group of straminipiles with world-wide distribution and occupying a high level of niche diversity that cannot be surpassed by any other straminpile or fungi. A wide range of variation in pathogenicity is observed in plant-associated species. Yet, some of the plant pathogenic species are among the most destructive, causing serious economic losses of crops by destroying seed, storage organs, roots, and other plant tissues. Since the description of P. monospermum by Pringsheim in 1858, more than 150 species have been reported. During the workshop, the future for Pythium systematics will be presented with the information for the species that will remain in Pythium sensu stricto, those that are transferred to Phytopythium gen.nov. and those that need to be repositioned to other genera like Artotrogus (1845) and Sphaerosporangium (1931).
Phytopythium
This new genus was erected recently which comprises the Pythium species from clade K in Lévesque & de Cock, and is morphologically and phylogenetically between Pythium andPhytophthora (Phytopythium Abad, de Cock, Bala, Robideau, Lodhi & Lévesque, gen. nov. 2010. Persoonia 24:136-137). It has globose to ovoid sporangia with papilla and often proliferating internally (Phytophthora-like). Zoospore discharge is Pythium-like: the sporangium forms a discharge tube through which the contents moves out and forms a vesicle at the tip with an undifferentiated mass of protoplasm which then differentiates into biflagellate zoospores. Most species have large, smooth oogonia, thick-walled oospores, and 1-2 elongate or lobate antheridia, laterally applied to the oogonium.
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