The powdery mildews belong to Ascomycota (Erysiphales) and are easily recognized by their conspicuous epiphytic mycelium. Anamorph state of most teleomorphic genera with exclusively external mycelium belong to the genus Oidium. Oidium states show a great deal of variation in morphology. Conidia are produced either in chains (Euoidium-type of the genus Oidium) or solitarily (Pseudoidium-type of the genus Oidium) which are hyaline, one-celled, uninucleate, vacuolate and thin-walled (Braun 1987). The length/width ratio and shape of conidia and foot-cells are usable for taxonomic purposes. The conidia of most Oidium species vary from cylindric, ellipsoid, ovoid to doliform and their surface is usually smooth. Khodaparast et al. (2000, 2001) and Pirnia et al. (2005–2007) have reported new species of powdery mildews in Iran. Ershad (2009) listed many taxa of Erysiphales. Khodaparast & Abbasi (2009) published a check-list of species, host range and geographical distribution of powdery mildew fungi in Iran.
One specimen obtained from Tehran was microscopically examined. Microscopic slides were prepared from conidiophores and conidia in 25% Lactic acid. Characters of mycelium (epiphyllous, hypophyllous or amphigenous; colour; density) conidia (single or in chains; shape, size, surface), conidiophores (size, shape and size of the foot-cells; number, size and arrangement of the following cells) and appressoria (shape) were used to identify species. Drawings were made using a drawing-tube attached to an Olympus BH2 microscope.
Anamorphic stage of Erysiphe syringae-japonicae on Jasminum is described and illustrated. The specimen is deposited in the fungal collection of Iranian Research Institute of Plant Protection (IRAN).
Erysiphe syringae-japonicae(U. Braun) U. Braun & S. Takam., Schlechtendalia, 4: 14 (2000).
Mycelium hypophylous, white, hyphae 3-7 µm wide; conidiophores erect, (52-) 67-100 (-120) µm long, foot-cells cylindrical to curved, 27-77 × 5-7 µm, usually followed by 1-2 shorter cells; conidia formed singly, ellipsoidal to cylindrical, 22-38 × 12-15 µm (Fig. 1).
Specimen examined: on Jasminum sp. (Oleaceae), Tehran, June 1, 2010. M. Pirnia (IRAN 16216 F).
The species is characterized by having short conidiophores and solitary conidia. In some conidiophores foot-cells were curved to sinuous in basal part.
Numerous records of powdery mildews have been reported on various plant genera in Oleaceae. Only Oidium jasmini was already been reported on Jasminum from India and there is no report of other powdery mildews on Jasminum (Braun 1987).
E. syringae-japonicae was originally found in East Asia on Syringa spp., which was described only based on teleomorphic stage (Braun 1987). This is the first report of anamorphic stage of this species on Jasminum.
Fig. 1. Erysiphe syringae-japonicae on Jasminum sp. (A) Conidiophores. (B) Curved foot-cell. (C) Conidia. (D) Germinated conidium. Specimen examined: on Jasminum sp. (Oleaceae), Tehran, June 1, 2010. M. Pirnia (IRAN 16216 F).