First report of leaf smut caused by Entyloma gaillardianum on Gaillardia aristata in Italy

Blanketflower (Gaillardia aristata) is a popular flowering plant commonly used in parks and gardens, belonging to Asteraceae. Starting in May 2017, 6-month-old plants grown in a private garden located near Biella (latitude, 45°36′00″N; longitude, 8°03′00″E) in Northern Italy showed signs and severe symptoms of a previously unknown disease. About 70% of the 30 G. aristata plants were affected, exhibiting circular spots on leaves, from 0.8 to 1.3 cm in diameter, sometimes coalescent. Amphigenous spots were light green and 6 to 9 days later turned brown and necrotic. Microscopic examination of leaf tissue sections showed sori composed by massive double-walled hyaline to yellowish spores in the intercellular spaces of the host tissue, ranging from 9.8 to 12.3 μm (mean, 10.5 μm) in diameter, typical of the teliospores of the genus Entyloma (Vanky 1982). Hyaline, cylindrical, nonseptate conidia from straight to curved, 12.5 to 19.5 × 2.5 to 3.8 μm, of the anamorphic stage were also observed. DNA was extracted from sori by using the E.Z.N.A. Fungal DNA Mini Kit (Omega BioTek). The internal transcribed spacer (ITS) regions of rDNA were amplified using the primers ITS1/ITS4 (White et al. 1990) and sequenced at the BMR Genomics Centre (Padua, Italy). The 442-bp product of this isolate (IT62) was deposited at GenBank (accession no. MF521597), and a BLASTn search showed a 100% similarity with Entyloma gaillardianum (accession no. AY081037). Pathogenicity was confirmed by spraying a spore suspension (5 × 104/ml), prepared from homogenized infested leaves, on three potted (3 liter) plants of G. aristata, and the same number of control plants were sprayed with sterile water. Plants were kept in a growth chamber at 21 to 24°C under 100% relative humidity for 5 days. All inoculated plants developed typical spots after 10 days, showing sori and spores similar to those previously described, whereas no symptoms developed on the control plants. Pathogenicity tests were carried out twice with the same results. Leaf smut caused by E. gaillardianum was reported on G. aristata in Germany, Israel, Romania, and Ukraine (Farr and Rossman 2017) and on Gaillardia × grandiflora in North America (Glawe et al. 2010). The presence of this pathogen is critical because Entyloma sp. causes severe economic losses on many different Asteraceae hosts, including Gaillardia sp. This is, to our knowledge, the first report of E. gaillardianum on G. aristata in Italy.