Archivio Journal of Plant Pathology

Abstract:

In March 2011, the presence of an unknown powdery mildew was observed on Euphorbia perdorfiana and E. aggregata, family Euphorbiaceae, growing in a farm near Ventimiglia (northern Italy). On E. perdorfiana, a conspicuous mycelium colonized stems and caused brown discolorations on ca. 50% of 7,500 plants. On E. aggregata, a white mycelium colonized leaves, spines and stem grooves, affecting ca. 60% of 4,000 plants. On both hosts, foot cells of the conidiophores were straight or slight- ly flexuous, followed by 3 shorter cells; conidia, with fibrosin bodies, were elliptical; chasmothecia were not observed. In the case of E. perdorfiana, conidia measured 25-33×14-18 μm; foot cells were 48-106 μm long; shorter cells measured 17-33×10-13 μm. In the case of E. aggregata, conidia measured 26-33×17-20 μm; foot cells were 62-97 μm long; shorter cells measured 14- 31×10-14 μm. For both pathogens, the ITS region of rDNA was amplified using the primers ITS1/ITS4 and sequenced (Altschul et al., 1997) (GenBank accession Nos. JX179220 and JX179218 for E. perdorfiana and E. aggregata respectively). BLAST analysis of the 513 bp amplicon (E. perdorfiana) and of the 523 bp ampli- con (E. aggregata) showed high homology with several sequences of Podosphaera spp. For both hosts, pathogenicity was confirmed by painting mycelia and conidia from infected tissues on five healthy plants. Several Sphaerotheca and Podosphaera species have been reported on the genus Euphorbia, e.g. P. euphorbiae-he- lioscopiae on E. pekinensis (Liu, 2011). This is the first report of Podosphaera sp. affecting E. perdorfiana and E. aggregata in Italy.