Archivio Journal of Plant Pathology

Abstract:

Verbascum nigrum “Album” is a perennial plant belonging to the spontaneous flora in Italy appreciated for the lasting white inflorescences. During the summer 2015, several plants of V. nigrum “Album” grown in gardens in the Biella province showed symptoms of a previously unknown powdery mildew. Leaves, stems and florets were covered with white mycelia. Conidiophores had a cylindrical foot cell measuring 94-188×11-15 (average 159×12) μm followed by 2 shorter cells, measuring 15-34×10-14 (average 20×12) μm. Conidia were elliptical to doliform, borne in short chains, measured 25-39×16-23 (average 34×21) μm and germinated apically. The Internal Transcribed Spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced (White et al., 1990) (GenBank Accession No. KT953356). The 524 bp amplicon had 100% homology with the sequence of Golovinomyces cichoracearum HQ316555. Pathogenicity was confirmed by spraying a conidial suspension (1.2×105 CFU/ml) onto leaves of three healthy plants of V. nigrum “Album”. Three control plants were treated with sterilised water. Fifteen days after inoculation, symptoms of powdery mildew developed only on inoculated plants. Erysiphe verbasci (Syn.: Golovinomyces verbasci), diffused only on Scrophulariaceae, was reported on V. nigrum in Europe (Braun, 1995). G. cichoracearum, widely diffused on Asteraceae, is reported on V. nigrum for the first time in Italy as well as worldwide.