First Report of Rhizoctonia solani AG-4 HG-I on Campanula trachelium in Italy

In the autumn of 2017, a crown rot was observed on three-month-old plants of Campanula trachelium growing in a nursery located in Grugliasco (Northern Italy). Petioles rotted at the base and leaves wilted. Finally, affected plants died. Rhizoctonia solani was consistently isolated from affected tissues. Colonies did not produce sclerotia. One of these isolates was paired with R. solani tester strains belonging to the anastomosis groups AG-1, AG-2, AG-4, AG-7, and AG-11. The hyphal fusions were observed microscopically only with the group AG-4 (Fusion Frequency < 30%) (Sneh et al. 1991). The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced (GenBank Accession number MG766874). BLASTn analysis (Altschul et al. 1997) of the 678 bp showed 99% identity with the sequence AY154307 of Thanatephorus cucumeris (teleomorph of R. solani). The high identity with a member of AG-4 HG-I led the R. solani isolated from C. trachelium to this subgroup (Gónzales et al. 2016). For pathogenicity tests, three two-month-old healthy plants of C. trachelium were inoculated with fragments (about 5 × 5 × 3 mm) of a single isolate of R. solani grown on potato dextrose agar (PDA). About seven days later, a crown rot started on inoculated plants and R. solani was constantly reisolated from affected petioles. R. solani AG-4 HG-I is reported on C. trachelium for the first time in Italy.