First Korean report of rosemary powdery mildew caused by Golovinomyces biocellatus

Rosemary (Rosmarinus officinalis) is a perennial herb with fragrant evergreen needle-like leaves. It is native to the Mediterranean region, and introduced to Korea in 1980s for ornamental, cooking and medicinal purposes. In November 2008several pot-grown rosemaryplants infected with a powdery mildew were found in a florist’s shop in Seoul, Korea. Tracing the epidemic of infection showed that nearly 100% of rosemary plants grown in polytunnels were infected with powdery mildew. According to the growers, rosemary powdery mildew was first noticed in 2007 summer and rather common in 2008 season. Symptoms first appeared as thin white colonies, which subsequently developed into abundant growth on both side of the leaves (Fig. 1). Severe infections often caused leaf distortions and premature senescence.

The hyphae were septate, branched, and 4-7 µm in width. Appressoria on the mycelium were nipple-shaped. Conidiophores were cylindrical, 110-170 x 9-12 µm, composed of 4-9 cells (Fig. 2). Conidia produced in chains were ellipsoid-ovoidto broadly oblong, 30-42 x 16-20 µm, lacking distinct fibrosin bodies, with linear, becoming rectangular, wrinkling of outer wall (Fig. 3). No chasmothecia were found but the above characteristics are consistent with Golovinomyces biocellatus as described by Braun (1987). DNA analysis was performed to confirm the identity of the fungus. The amplification of the ITS rDNA region was performed with primers ITS5 and P3 using the thermal cycling conditions described by Takamatsu et al. (2009). The ITS sequence (GenBank FJ874774) was identical to Golovinomyces biocellatusex. Rosmarinus officinalis (AB307672). Therefore, the sequence analysis verified the fungus to be G. biocellatus.

Several species of powdery mildew fungi have been recorded onrosemary (Farr & Rossman, 2009). Leveillula spp. recorded from Europe and Podosphaera fuliginea from USA, are easily differentiated from this fungus. Neoerysiphe galeopsidis was reported from Europe, New Zealand, South Africa, and recently from Japan (Tanda & Hirose, 2003). Golovinomyces biocellatus, however, was known only from South Africa and California, USA (Glawe, Takamatsu & Koike, unpublished). This is the first report of powdery mildew on rosemaryassociated with G. biocellatus in Asia, suggesting that this fungus is spreading worldwide.