FIRST REPORT OF VERTICILLIUM WILT, CAUSED BY VERTICILLIUM DAHLIAE, ON RUDBECKIA HIRTA IN ITALY

Abstract

At the end of summer 2011, symptoms of vascular wilt and stunting were observed on Rudbeckia hirta (black-eyed Susan) plants grown in a private garden near Biella (northern Italy). Symptoms were yellowing of external leaves and brown or black streaks in the vascular tissue of roots, crowns, and leaves. Verticil- lium dahliae (Pegg and Brady, 2002) was consistently and readily isolated onto PDA from symptomatic vascular tissue disinfected in 1% NaClO. Dark microsclerotia, irregular in shape, and 37 to 102 μm, developed in association with hyaline hyphae after 10 days of growth at 23±1°C and 12 h photoperiod. Hyaline, ellipti- cal, single-celled conidia measuring 3.0-7.5×2.3-3.6 μm (average 4.5×2.7 μm) developed on verticillate conidiophores. The ITS re- gion of rDNA was amplified using primers ITS1/ITS4 and se- quenced (Altschul et al., 1997). The 518 bp amplicon (GenBank accession No. JX276654) showed 98% homology with V. dahliae. Healthy, 20-day-old R. hirta plants were inoculated by roots im- mersion into a conidial suspension (1.0×106 CFU/ml). Non-inoc- ulated plants served as controls. Plants were grown in pots (2 liter volume) in a steam disinfested potting mix (black and white peat), and maintained in a glasshouse at 20-22°C. First symptoms and vascular discolorations were observed 20 days after inocula- tion. Non-inoculated plants remained healthy. The pathogenicity tests were carried out twice. V. dahliae was consistently reisolated from inoculated plants. To our knowledge, this is the first report in Italy of V. dahliae on R. hirta.