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First Report of Powdery Mildew Caused by Golovinomyces biocellatus on Common Sage (Salvia officinalis) in Slovenia

Common sage (Salvia officinalis) is a well known perennial and medicinal herb in the Lamiaceae family, which is widely planted in gardens and parks in Slovenia. In September 2007, symptoms of powdery mildew infection were observed on common sage plants grown in several gardens in the Savinja valley. White mycelium was present, principally on the upper leaf surface, but was also observed on stems. The disease progressed as spots coalesced and leaves become distorted and necrotic. Microscopic observations revealed septate and branched hyaline hyphae 4 to 7 μm wide. Conidiophores were cylindrical and septate and measured 40 to 90 × 9 to 12 μm. The foot cells of the conidiophores were straight, followed by one to three shorter cells. Conidia produced in chains (three to four conidia per chain) were hyaline and doliform in shape, measuring 27 to 35 × 14 to 20 μm and lacking fibrosin bodies. Cleistothecia were not observed in the collected samples. All of these characteristics were consistent with Golovinomyces biocellatus as described by Braun (2). For molecular identification of the pathogen, DNA was extracted from mycelia and conidia of infected plants, collected in two different gardens in the Savinja valley as representative samples (1GB-Sof and 2GB-Sof). Nuclear rDNA internal transcribed spacer (ITS) regions were amplified by PCR using the universal primers ITS4 and ITS5, and sequenced. Both samples yielded the same 532 bp sequence, which showed the highest identity (97 to 99%; E value = 0.0) to G. biocellatus ITS sequences in the NCBI GenBank (1). The nucleotide sequence has been assigned GenBank Accession No. JQ340358. Pathogenicity was confirmed by inoculation of 10 healthy plants of S. officinalis ‘Grower's Friend’ planted in pots. Plants were sprayed with a spore suspension (10⁵ conidia/ml; 0.01% Tween 20) obtained from naturally infected leaves. Inoculated plants were covered with polyethylene bags for two days to maintain high humidity and incubated in a growing chamber at 22°C with a 12-h photoperiod. The first powdery mildew signs and symptoms developed on leaves 7 days after inoculation. Ten control plants sprayed with distilled water showed no symptoms. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants. Powdery mildew infections of common sage associated with G. biocellatus have been known in Argentina, Washington State (United States), and various countries in Europe (2,3,4). To the best of our knowledge, this is the first report of G. biocellatus on common sage in Slovenia. Voucher specimens are available at the culture collection of the Slovenian Institute of Hop Research and Brewing.

References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (3) M. G. Cabrera et al. Mycosphere 1:289, 2010. (4) F. M. Dugan. North American Fungi 6:1, 2011.