Archivio Journal of Plant Pathology

Abstract:

At the end of summer 2012, symptoms of a previously un- known powdery mildew were observed on Impatiens New Guinea (Impatiens x hawkeri) grown in a nursery and in a private garden near Torino (northern Italy). A white conspicuous myceli- um colonized leaves and stems, causing brown discolorations and distortion of infected tissues. Ten per cent of the plants in the nursery and all plants in the garden were affected. Conidiophores were erect, with a foot cell straight or slightly flexuous, followed by 1-2 shorter cells; conidia, with fibrosin bodies, were hyaline, elliptical, borne in short chains; chasmothecia were not observed. Conidia measured 25-33×15-19 (average: 31×18) μm; conidio- phores foot cells were 51-120×10-12 (average: 72×12) μm; shorter cells measured 12-34×10-12 (average: 20×10) μm. The ITS region of rDNA was amplified using the primers ITS1/ITS4 (White et al., 1990) and sequenced (GenBank accession No. JX876488). BLAST analysis of the 513 bp amplicon showed 99% and 100% identity with Podosphaera balsaminae and P. xanthii, respectively. Pathogenicity was confirmed by painting mycelia and conidia from infected tissues on five healthy plants. Control plants re- mained symptomless. Considering that the taxonomy of causal agent of powdery mildew on Impatiens species is very confused, the new diseases is reported as caused by Podosphaera sp. Several species of Sphaerotheca and Podosphaera have been reported on the genus Impatiens, such as P. balsaminae on Impatiens balsami- na and Impatiens x hawkeri in Argentina (Wolcan, 2004).