First Report of Erysiphe sp. as a Causal Agent of Powdery Mildew on Punica granatum in Italy

Punica granatum L. (pomegranate), belonging to the Punicaceae family, is a plant native to the Middle East. Its fruit has gained widespread popularity as a functional and nutraceutical food and hence, pomegranate growing has noticeably increased in southern Italy from 43 ha in 2010 to 168 ha in 2015 (http://agri.istat.it/). In June 2015, a severe outbreak of powdery mildew was observed on 70% of 450,000 2-year-old pomegranate plants cvs. Wonderful One and Ako in a nursery located in Lecce Province, Italy. White, dense plaques of mycelium and conidia covering 30 to 40% of the young leaves were observed. At later stages of disease development, leaves turned yellow and abscised. No chasmothecia were detected. The conidiophore foot cell was cylindrical and the appressorium lobed. Microscopic observations of 300 conidia from each of 10 plant samples showed that they were hyaline, ellipsoid to cylindrical, measuring 28.1 to 35.7 × 12.9 to 14.4 μm (average 32.8 × 13.4 μm), fibrosin bodies were absent, and the germ tube was subterminal. ITS genomic regions were sequenced for molecular identification. DNA was extracted from conidia and mycelium by using InstaGene Matrix (Bio-Rad Laboratories, Hercules, CA), amplified by PCR using the universal ITS5/ITS4 primers, and the amplicon was sequenced by external service (Macrogen, Seoul, South Korea). BLASTn analysis of the ITS sequence (563 bp) showed a high homology (identity: 99%; e-value: 0.0; coverage: 99%) with species of the Erysiphe aquilegiae clade (i.e., E. aquilegiae [EU047570.1], E. sedi [JX173288.1], Pseudoidium hortensiae [JQ669944.1], and P. neolycopersici [GU358451.1]) (Takamatsu et al. 2015). Artificial inoculations were made by gently pressing naturally diseased leaves onto 20 young fully expanded leaves of 10 healthy potted plants cv. Wonderful One grown under glasshouse conditions at 25 ± 2°C. Five noninoculated plants served as controls. Typical powdery mildew symptoms developed within 7 to 10 days only on inoculated leaves. Therefore, on the basis of morphological features, the pathogen was tentatively identified as Erysiphe sp. and, according to the BLASTn results, it appears to belong to the still unresolved E. aquilegiae clade. The ITS sequence was deposited in GenBank under accession number KU060880. E. punicae T.M. Achundov, whose gene sequences are not available, was reported as the causal agent of powdery mildew on pomegranate in Azerbaijan (Akhundov 1987), Iran (Khodaparast and Abbasi 2009), and Montenegro; anamorphs of powdery mildews on pomegranate were also recorded from Ethiopia, Greece, India, Iraq, Ukraine, and Crimea but it is unclear if they belong to E. punicae (Braun and Cook 2012). This is the first report of powdery mildew on pomegranate in Italy. Due to the poor availability of fungicides allowed on the crop, improved disease management methods are needed to prevent heavy yield losses. References: Akhundov, T. M. 1987. Nov. Sist. Niz. Rast. 24:95. Braun, U., and Cook, R.T.A. 2012. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, The Netherlands. Khodaparast, S. A., and Abbasi, M. 2009. Mycotaxon 108:213. 10.5248/108.213. Takamatsu, S., et al. 2015. Mycologia 107:475. 10.3852/15-007