First report of Verticillium wilt, caused by Verticillium dahliae, on Phlox paniculata in Italy.

Abstract

During summer 2013, several plants of Phlox paniculata growing in gardens located in the Biella province (Northern Italy) showed symptoms of vascular wilt. Symptoms were yellowing of the leaves and brown streaks in the vascular tissue. Eventually, plants wilted and died. A fungus was consistently isolated on potato dextrose agar (PDA) from symptomatic vascular tissues. Dark, irregular microsclerotia, 24-101×14-68 (average 58×26) μm in size developed in hyaline hyphae and elliptical single-celled conidia, 2.8-4.7×1.2-3.0 (average 3.8×2.2) μm in size developed on verticillate conidiophores. The fungus was identified as Verticillium dahliae (Pegg and Brady, 2002). The Internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced (GenBank accession No. KM000048). BLASTn analysis (Altschul et al., 1997) of an amplified product 496 bp in size showed 100% homology with the sequence of V. dahliae AB551206. Three healthy plants of P. paniculata were inoculated by root immersion into a conidial suspension (0.4×107 CFU/ml) of one isolate of the pathogen. Three non-inoculated plants served as controls. First wilt symptoms and vascular discoloration developed 40 days post inoculation only on inoculated plants and V. dahliae was readily reisolated. V. dahliae on P. paniculata was reported in USA and Canada. To our knowledge, this is the first report of V. dahliae on P. paniculata in Italy.