The present study on oomycetous fungi of Sindh province yielded 42 species of Oomycetes belonging to 10 genera. Of these, four species viz., Pythium mirpurum sp. nov., Pythium sindhum sp. nov., Pythium musanium sp. novo and Pythium karachinium sp. novo are new to science. A total of 28 species isolated for the first time from Pakistan are: Achlya bisexualis, Dictyuchus monosporus, Pythium acanthicum, Pythium adhaerens, Pythium angustatum, Pythium boreale (syn: Pythium megacarpum), Pythium campanulatum, Pythium carolinianum, Pythium catenulatum (syn: Pythium rhizo-oryzae), Pythium chamaehyphon, Pythium debaryanum, Pythium deliense, Pythium dissotocum (syn: Pythium coloratum, Pythium lutarium, Pythium marinum), Pythiumflevoense (syn: Pythium capillosum, Pythium pectinolyticum), Pythium graminicola (syn: Pythium periilum), Pythium hydnosporum (syn: Pythium oligandrum, Pythium amasculinum), Pythium irregulare, Pythium litorale (syn: Pythium sterilum), Pythium oedochilum, Pythium ostracodes, Pythium plurisporium, Pythium sulcatum, Pythium sylvaticum, Pythium torulosum (syn: Pythium folliculosum), Pythium ultimum var. ultimum, Pythium vexans, Saprolegnia ferax and Saprolegnia hypogyna. Alongwith all above mentioned species, Pythium middletonii, Pythium spinosum (syn: Pythium kunmingense), Phytophthora nicotiane appeared to be new records from Sindh province. Beside these some of already reported species such as Pythium aphanidermatum (syn: Pythium butleri), Albugo candida, Bremia lactucae, Peronospora destructor, Pseudoperonospora cubensis, Peronospora parasitica and Sclerospora graminicola were also encountered. All these species do not represent our whole collection of Oomycetes isolated during the study, as our molecular results revealed that there are about 25 new putative species, which need to be described are present in our collection.
Molecular analysis placed fairly large number of described species as synonyms. A partial DNA LSD (DI-D3) analysis of the diverse range of genera and species within the oomycetes revealed that resulting molecular phylogeny is mostly in accordance with those of traditional morphology based phylogeny with some differences. The genus Albugo assumed an intermediate position between Peronosporomycetidae and Saprolegniomycetidae, rather than within Peronosporales (subclass: Peronosporomycetidae). Also, the downy mildew causing organisms (Peronospora, Bremia, Pseudoperonospora) which are classified in order Peronosporales were found to be closely related with Phytophthora species (order: Pythiales) according to molecular analysis. The genus Pythiogeton is traditionally classified in order Pythiales alongwith Pythium and Phytophthora but molecular analysis definitely placed all members of the genus Pythiogeton within genus Pythium, the LSD data would tend to support the deletion of the genus status of Pythiogeton and to include its members in the genus Pythium where they appear to represent in a new Pythium clade. The LSD phylogenetic analysis revealed that the members of Pythium clade K or Pythium vexans group (P. oedochilum, P. boreale, P. megacarpum, P. chamaehyphon, P. ostracodes, P. litorale, P. sterilum, P. vexans, P. carbonicum, P. montanum, P. helicoides, P. indigoferae, P. curcurbitacearum) are closely related with members of the genus Phytophthora than other members of the genus Pythium. Our study confirmed that members of clade K are phylogenetically distantly related as well as differ from other clades of Pythium. Therefore, one new genus Pythiophthora within Pythiales for the members of clade K is proposed.