Archivio Journal of Plant Pathology

Abstract:

Symphyotrichum subulatum var. squamatum (Spreng.) S.D.Sundb. (Syn: Conyzanthus squamatus) is one of the weed which occurs in many regions of south Caspian Sea, especially around rice fields and along road sides, where more water is available. In June 2014, a powdery mildew was observed on C. squamatus in Guilan and Mazandaran provinces. Symptoms first appeared as small, nearly circular white spots that enlarged and coalesced over time. As the disease progressed, a white mycelium covered the entire plant. Conidiophores were erect 80-146.5 × 10-14 μm in size and bore 2-4 immature conidia in short chains with sinuate edge-line, measuring 21-43×17-24 μm. Conidia were hyaline and cylindrical and lacked distinct fibrosin bodies. Long, unbranched germ tubes grew from the ends of conidia. These morphological characteristics suggested that the powdery mildew fungus is Golovinomyces cichoracearum (anamorph Euoidium sp.)(Braun, 1987). Chasmothecia were not observed in the collected samples. To confirm the morphological identification, the ITS-rDNA region was amplified using the primer pair ITS4/ITS5 (White et al., 1990) and sequenced (GenBank accession No. KM434159). Blast analysis of the 563 bp amplicon showed 99% similarity with G. cichoracearum (EU233820). Pathogenicity was ascertained on healthy potted host plants, inoculated by touching them with mildew- infected leaves. Non-inoculated plant served as controls. After 5-7 days, a fungus developed on inoculated plants with a morphology matching that of the original pathogen. Non-inoculated control plants did not develop powdery mildew symptoms. To our knowledge, this is the first report of G. cichoracearum-induced powdery mildew on C. squamatus in Iran, whereas a powdery mildew caused by Oidium sp. had previously been recorded on this plant (Aeenfar, 2006).