First report of powdery mildew of Sideritis perfoliata caused by Neoerysiphe galeopsidis in Cyprus

Abstract

The genus Sideritis L. (Lamiaceae) comprises approximately 150 perennial and annual species, mainly in the Mediterranean Basin, and has been used traditionally for culinary and therapeutical purposes (González-Burgos et al. 2011). Medicinal and aromatic plants (MAPs) constitute a dynamic sector for Cyprus due to the ideal prevailing climatic conditions and the relatively limited required crop resources. Currently, MAPs are grown on approximately 160 ha in Cyprus exported mainly to European markets. During the winter of 2014, 0.4 ha of Sideritis perfoliata plants grown on an organic farm near Nicosia were severely affected by a foliar disease that rendered the crop unmarketable. Symptoms included yellow, spotty discoloration of infected leaves that resulted in wilting and necrosis. Signs resembled those of a powdery mildew. Mycelium was sparse and not easily noticed on the upper leaf area due to the density of trichomes. Conidiophores were hyaline and straight, with 2 to 5 hyaline, doliform conidia that lacked fibrosin bodies and ranged from 35 to 49 μm (mean ± standard deviation of 42 ± 4 μm) × 17 to 25 μm wide (mean = 21 ± 3 μm). Chasmothecia were abundant, partly clustered, yellowish to dark brown, globose, 102 to 203 μm in diameter (157 ± 38 μm) each containing 5 to 8 asci. Numerous hyaline, septate, mycelioid appendages, generally simple and rarely branched, were observed on the chasmothecia. Asci were stalked, kidney-shaped, and ranged from 42 to 90 μm (58 ± 17 μm) × 18 to 35 μm (25 ± 5 μm). No mature ascospores were found on the examined specimens. The microscopic features were consistent with those of Neoerysiphe galeopsidis (DC.) U. Braun (Braun and Cook 2012). For molecular identification, fungal genomic DNA of isolate NG_CY1 was extracted from infected tissue and part of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) region was amplified using primers ITS5 and P3 according to Takamatsu et al. (2009). The PCR product was sequenced. BLAST analysis of the 548-bp fragment (GenBank Accession No. KR006933) showed ≥99% similarity to N. galeopsidis ITS sequences in the NCBI database (AB498942, AB498949, DQ359698, and AB022370). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of five healthy plants of S. perfoliata. An equal number of noninoculated plants served as control plants. All plants were covered with polyethylene bags for 2 days and incubated in a growth chamber at 24°C, after which they were uncovered and maintained at the same temperature with a 12-h photoperiod. Powdery mildew signs and symptoms were first observed approximately a week later. The fungus that developed was morphologically identical to that observed on the original diseased plants, while no symptoms developed on the control plants, therefore, Koch’s postulates were fulfilled. Although N. galeopsidis has been reported on plants from 12 families, mainly species in the Lamiaceae, and on other Sideritis species (Farr and Rossman 2015, Pastircakova et al. 2008), to our knowledge this is the first report of powdery mildew caused by N. galeopsidis on S. perfoliata in Cyprus.